Measurements of Ca2+ entry and sarcoplasmic reticulum Ca2+ content during the cardiac cycle in guinea pig and rat ventricular myocytes

This study investigates the contribution of Ca2+ entry via sarcolemmal (SL) Ca2+ channels to the Ca2+ transient and its relationship with sarcoplasmic reticulum (SR) Ca2+ content during steady-state contraction in guinea pig and rat ventricular myocytes. The action potential clamp technique was used to obtain physiologically relevant changes in membrane potential. A method is shown that allows calculation of Ca2+ entry through the SL Ca2+ channels by measuring Cd(2+)-sensitive current during the whole cardiac cycle. SR Ca2+ content was calculated from caffeine-induced transient inward current. In guinea pig cardiac myocytes stimulated at 0.5 Hz and 0.2 Hz, Ca2+ entry through SL Ca2+ channels during a cardiac cycle was approximately 30% and approximately 50%, respectively, of the SR Ca2+ content. In rat myocytes Ca2+ entry via SL Ca2+ channels at 0.5 Hz was approximately 3.5% of the SR Ca2+ content. In the presence of 500 nM thapsigargin Ca2+ entry via SL Ca2+ channels in guinea pig cardiac cells was 39% greater than in controls, suggesting a larger contribution of this mechanism to the Ca2+ transient when the SR is depleted of Ca2+. These results provide quantitative support to the understanding of the relationship between Ca2+ entry and the SR Ca2+ content and may help to explain differences in the Ca2+ handling observed in different species.     

Cardiovascular effects of the K-ATP channel blocker U-37883A and structurally related morpholinoguanidines

The cardiovascular effects of the K-ATP channel blocker U-37883A and 5 related morpholinoguanidines were determined in 6 experimental preparations. In anesthetized dogs, U-37883A (0.5-8.0 mg/kg i.v.) increased mean arterial pressure (MAP; +18%) and left ventricular (LV) effective refractory period (ERP; +35%), and decreased LV contractility (-41%). Higher doses of U-37883A (16-32 mg/kg) fatally reduced MAP (-84%), heart rate (HR; -57%) and LV contractility (-72%). In anesthetized rats, U-37883A (1.0-50 mg/kg i.v.) also maximally reduced MAP, HR and LV contractility by 68, 77 and 48%, respectively. U-37883A and its analogs were diuretic in conscious rats (1.5-15 mg/kg i.v.) and blocked pinacidil in rabbit mesenteric artery (EC50 = 0.5-50 microM). In rabbit papillary muscle, 50 microM U-37883A significantly reduced force of contraction (-33%) and prolonged conduction time (+244%). Milder papillary effects were seen with the N'-OH analog U-45194A, which did not depress LV contractility in intact rats. In conscious dogs, oral U-45194A (50 mg/kg) was diuretic but reduced LV stroke volume and increased peripheral vascular resistance. These studies characterize U-37883A's systemic cardiovascular and direct myocardial effects, and identify U-45194A as a less cardiac depressant analog having U-37883A-like diuretic and functional K-ATP channel blocking activities.     

Complications associated with rapid caffeine application to cardiac myocytes that are not voltage clamped

The rapid application of caffeine to cardiac myocytes is commonly used to assess changes in the Ca2+ content of the sarcoplasmic reticulum (SR) and to study other parameters of intracellular Ca2+ regulation. Here we examined the effects of rapid caffeine application on membrane potential, intracellular Ca2+, and cell shortening in ventricular myocytes (rat, rabbit, guinea pig, dog) and atrial myocytes (rabbit) that were not voltage clamped. Conditioning pacing was used to achieve a steady-state level of SR Ca2+ loading prior to caffeine (10 mM) application. Caffeine transiently depolarized myocytes as expected from activation of forward Na+-Ca2+ exchange. However, we also found in each species (50% rat, 36% rabbit ventricular, 53% rabbit atrial, 56% guinea pig, 31% dog) that the caffeine-induced depolarization could also trigger an action potential. Caffeine-triggered potentials were completely blocked by thapsigargin (1 microM). The Ca2+ transient and contraction that accompanied caffeine-triggered action potentials had a larger magnitude and slower rate of decline (or relaxation) than occurred during caffeine-induced subthreshold depolarizations. Thus, the use of rapid caffeine application to study SR function and [Ca2+]i regulation in myocytes that are not voltage clamped can yield erroneous results.     

Antiasthmatic activity of the second-generation phosphodiesterase 4 (PDE4) inhibitor SB 207499 (Ariflo) in the guinea pig

We evaluated the airway activity of the novel phosphodiesterase type 4 inhibitor SB 207499 [Ariflo; c-4-cyano-4-(3-cyclopentyloxy-4-methoxyp henyl-r-1-cyclohexane carboxylic acid)], in the guinea pig. Ovalbumin (OA)-induced contractions of guinea pig isolated tracheal strips were inhibited by SB 207499 with an EC50 of 1 microM but had little or no effect on exogenous agonist-induced contraction, which suggests that its effect on OA-induced contraction in vitro is primarily due to inhibition of mediator release from mast cells. In anesthetized guinea pigs, SB 207499 inhibited OA-induced bronchoconstriction with i.v. and p.o. ID50 values of 1.7 and 17 mg/kg, respectively. At 1, 3 and 6 hr after SB 207499 (30 mg/kg p.o.), OA-induced bronchospasm was inhibited by 92%, 70% and 58%, respectively, corresponding to elevated plasma concentrations of 1.62 +/- 0.19, 1.65 +/- 0.29 and 0. 93 +/- 0.24 microg/ml, respectively, of SB 207499. SB 207499 also inhibited house dust mite-induced bronchoconstriction (ID50 = 0.9 mg/kg i.v. and 8.9 mg/kg p.o.). In contrast to its lack of bronchorelaxant activity in vitro, SB 207499 inhibited bronchospasm induced by i.v. leukotriene D4 (LTD4) [ID50 = 3 mg/kg i.v.]. The bronchorelaxant effect of i.v.-administered SB 207499 was at least additive with that of salbutamol in reversing infused histamine-enhanced airway tone, but it did not alter base line or enhance salbutamol-induced cardiovascular effects. In conscious guinea pigs, SB 207499 (10 or 30 mg/kg p.o.), 1 hr before antigen or LTD4 challenge, markedly reduced bronchospasm and subsequent eosinophil influx as measured by bronchoalveolar lavage 24 hr after provocation. SB 207499 administered after OA or LTD4 challenge also reduced airway eosinophilia measured at 24 hr after OA challenge or 96 hr after LTD4 challenge. These results, coupled with the broad anti-inflammatory activity of SB 207499 previously described (Barnett et al., 1998), suggest that SB 207499 will be useful in the treatment of asthma and other inflammatory disorders.     

Expression and activity of 3beta-hydroxysteroid dehydrogenase/delta5-delta4-isomerase in the rat Purkinje neuron during neonatal life

Diadenosine tetraphosphate (AP4A) is an endogenous compound and exerts diverse physiological effects in animal systems. However, the effects of AP4A on inotropy in ventricular cardiac preparations have not yet been studied. The effects of AP4A on force of contraction (FOC) were studied in isolated electrically driven guinea pig and human cardiac preparations. Furthermore, the effects of AP4A on L-type calcium current and [Ca]i were studied in isolated guinea pig ventricular myocytes. In guinea pig left atria, AP4A (0.1-100 microM) reduced FOC maximally by 36.5 +/- 4.3%. In guinea pig papillary muscles, AP4A (100 microM) alone was ineffective, but reduced isoproterenol-stimulated FOC maximally by 29.3 +/- 3.4%. The negative inotropic effects of AP4A in atria and papillary muscles were abolished by the A1-adenosine receptor antagonist 1, 3-dipropyl-cyclopentylxanthine. In guinea pig ventricular myocytes, AP4A (100 microM) attenuated isoproterenol-stimulated L-type calcium current and [Ca]i. In human atrial and ventricular preparations, AP4A (100 microM) alone increased FOC to 158.3 +/- 12.4% and 167.5 +/- 25.1%, respectively. These positive inotropic effects were abolished by the P2-purinoceptor antagonist suramin. On the other hand, AP4A (100 microM) reduced FOC by 27.2 +/- 7.4% in isoproterenol-stimulated human ventricular trabeculae. The latter effect was abolished by 1,3-dipropyl-cyclopentylxanthine. In summary, after beta adrenergic stimulation AP4A exerts negative inotropic effects in animal and human ventricular preparations via stimulation of A1-adenosine receptors. In contrast, AP4A alone can exert positive inotropic effects via P2-purinoceptors in human ventricular myocardium. Thus, P2-purinoceptor stimulation might be a new positive inotropic principle in the human myocardium.     

Laccase from the white-rot fungus Trametes versicolor: cDNA cloning of lcc1 and expression in Pichia pastoris

The influence of thapsigargin, a selective inhibitor of sarcoplasmic reticulum (SR) Ca2+ ATPase, on the positive inotropic effects of digoxin before and after pretreatment with rimalkalim [(3S,4R)-3-hydroxy-2,2-dimethyl-4-(oxopyrrolidinyl)-6-phenyl-su lfonylchroman hemihydrate (formerly HOE 234)], a known activator of ATP-sensitive K+ channels, was studied in the guinea pig heart. The isolated papillary muscles from the guinea pig heart were used to study these effects. The following parameters were measured: force of contraction (Fc), rate of rise (+dF/dt) and rate of fall (-dF/dt) of Fc, time to peak contraction (ttp) and time to 10% of the total amplitude of force (tt10). After pretreatment with rimalkalim (1 microM), digoxin caused a significant increase in the amplitude of Fc and significant shortening of ttp and tt10 (p < 0.05 compared with the values obtained with digoxin alone). Thapsigargin (1 microM), a selective inhibitor of sarcoplasmic reticulum Ca2+ ATPase, added to rimalkalim, prevented the enhancement of the amplitude of Fc induced by digoxin after pretreatment with rimalkalim but had no significant influence on the effects of digoxin itself. The results demonstrate significant influence of activation of KATP channels on digoxin-induced positive inotropic effects in the guinea pig heart. Attenuation of this effects of rimalkalim by addition of thapsigargin suggests that activation of SR Ca2+ ATPase can be included in this interaction.     

The size of the subpopulation susceptible to malignant neoplasm of the brain

The effects of acute and chronic glutathione depletion (single i.p. injection of 3 mmol/kg L-buthionine-S,R-sulphoximine and 2 mmol/kg for 4 days) on heart action potential (AP) characteristics, electronmicroscopy, cytochemistry and biochemistry and vascular contractility and nitric oxide-mediated relaxation were studied in rats and guinea pigs. In guinea pig cardiac preparations both acute and chronic glutathione depletion caused a significant decrease of maximum rate of rise of depolarization phase and duration of action potential AP(APD) at 25, 50, and 90% of repolarization but did not modify the other AP parameters. The contractile responses of helically cut aortic strips to norepinephrine were not altered by chronic glutathione depletion but the relaxing responses of precontracted preparations to acetylcholine were significantly reduced both in rats and guinea pigs. Morphologically there were indications of permeability changes, intracellular and interstitial edema and myofilament damage in the myocardium. There was also a decrease in cytochromoxydase and succinyl dehydrogenase activities both in rats and guinea pigs. The present data suggest that glutathione depletion may influence the Na+ and K+ channel activities, causes morphological and biochemical changes in cardiac preparations and may interfere with nitric oxide generation or its action in aortic strips.     

Effect of phorbol ester, 12-deoxyphorbol 13-isobutylate (DPB), on muscle tension and cytosolic Ca2+ in rat anococcygeus muscle

Effects of phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), on muscle tension and cytosolic Ca2+ ([Ca2+]i) level was investigated in rat anococcygeus muscle in comparison with other smooth muscles. 1) DPB (10(-6) M) induced a large contraction and an elevation of [Ca2+]i level in rat aorta and small and rhythmic changes in tension and [Ca2+]i level in guinea pig ileum. However, DPB did not change either of the parameters in rat anococcygeus muscle. 2) DPB caused tension development without changing the [Ca2+]i level elevated by high K+, ionomycin or beta-escin in the anococcygeus muscle. 3) In the beta-escin permeabilized muscles of guinea pig ileum and urinary bladder, rabbit mesenteric artery and rat anococcygeus muscle, DPB enhanced the Ca(2+)-developed tension. Moreover, the enhancement was inhibited by H-7 (3 x 10(-5) M). 4) DPB did not cause muscle tension to develop in the muscle of rat aorta, guinea pig ileum and rat anococcygeus muscle, pretreated with phorbol 12-myristate 13-acetate for 24 hr. In conclusion, DPB showed different contractile effects on the aorta, ileum and anococcygeus muscle, respectively. The initiation of muscle tension by DPB probably requires [Ca2+]i and the DPB-induced enhancement may be due to a Ca2+ sensitization of contractile elements in the anococcygeus muscle. Therefore, the difference between the DPB-induced response of the anococcygeus muscle and those of the other muscles seems to be due to a different Ca2+ movement caused by DPB. Moreover, it is suggested that DPB develops muscle tension by increasing [Ca2+]i and enhances it through the mediation of protein kinase C in the anococcygeus muscle as well as the other smooth muscles.     

Pharmacodynamics of 2-(4-benzyl-piperidino)-1-(4-hydroxyphenyl)-1-propanol (Ifenprodil). (3) Effects on the autonomic, peripheral and central nervous systems

Effects of ifenprodil tartrate, a potent vasodilator, on the autonomic, peripheral and central nerve system were studied in experimental animals. In isolated vas deferens of guinea pigs, the contraction in response to noradrenaline and sympathetic nerve stimulation was competetively antagonized by ifenprodil 10(-7)--10(-5) M (pA2: 7.69 against noradrenaline). Ifenprodil (50 approximately 1,000 mug/kg i.v.) inhibited the contraction of cat nictitating membrane and dog urinary bladder induced by sympathetic nerve stimulation. Ifenprodil (250 approximately 1,000 mug/kg i.v.) lowered adrenaline-induced lethality (ED50: 360 mug/kg). The drug produced a hypermotility of guinea pig uterus, and showed a transient hypertonus of dog gut which was abolished by atropine. Ifenprodil (10 approximately 20 mg/kg i.v.) inhibited the propulsion of charcoal meal in mice. In Shay rats, more than 10 mg/kg i.m. of the drug inhibited the secretion of acid gastric juice and the ulceration. Ifenprodil showed a potent local anesthetic action in the guinea pig cornea and skin. The spontaneous EEG of rabbits showed a resting pattern (0.25 approximately 2 mg/kg i.v.) followed by an arousal pattern (5 approximately 10 mg/kg). Ifenprodil (20 approximately 100 mg/kg p.o.) potentiated a hypnosis induced by barbital, and potentiated pentylenetetrazol, strychnine and picrotoxin induced convulsion. The drug (20 and 100 mg/kg p.o.) lowered the body temperature of rats. From these results it is concluded that ifenprodil produces a blocking action of alpha-adrenoceptors in various smooth muscle preparations and a direct relaxation of the smooth muscle itself without affecting the motor and central nerve systems.     

A comparison of the generalization of behavioral marital therapy and enhanced behavioral marital therapy

The pharmacological effects of verapamil and GS 283, 1-(4'-methoxybenzyl)-6,7-dihydroxy-3,4-dihydroxyisoquinoline, were investigated using isolated rat and guinea pig trachealis. Both verapamil and GS 283 inhibited carbachol-, histamine (only guinea pig)-, and high-K(+)-induced contraction in a dose-dependent manner. GS 283 acted as a weak histamine H1 and muscarinic receptor antagonist in guinea pig and rat trachealis with respective pKB values in the range of 5.60 approximately 6.12 and 5.17 approximately 5.83. On the other hand, pyrilamine and atropine showed a typical competitive antagonism on histamine (guinea pig) and on muscarinic receptors (rat trachea) with pKB values of 9.25 +/- 0.21 and 9.37 +/- 0.32, respectively. GS 283 inhibited Ca(2+)-induced contraction on guinea pig trachealis in Ca(2+)-free media. Furthermore, very high concentrations of GS 283 and verapamil completely abolished a phasic contraction induced by carbachol in Ca(2+)-free media, suggesting that verapamil and GS 283 can enter into the cytoplasm, where they may exert secondary actions on internal sites of the muscle, such as the sarcoplasmic reticulum. It is concluded that GS 283 has a Ca2+ antagonistic action along with weak histamine and muscarinic receptor blocking activity in isolated rat and guinea pig tracheal smooth muscle and its mode of action is likely inhibition of Ca2+ influx from plasma membrane and also release from the sarcoplasmic reticulum.     

Fungal products. Part XVII. Microbiological hydroxylation of gibberellin A9 and its methyl ester

Angiotensin II (A II) and analogues were tested for their ability to restore electrical and mechanical activity to cardiac muscle preparations in which the fast Na+ channels had been inactivated by partial depolarization (22-27 mM K+) or by tetrodotoxin (TTX). The partially depolarized or TTX-blocked preparations were chosen because under these conditions electrical and mechanical responses are primarily Ca2+ -dependent. In depolarized rabbit right atria, A II restored spontaneous mechanical and electrical activity (measured by both intracellular and extracellular recording techniques). The frequency of action potential discharge was concentration-dependent; the threshold concentration of A II was 10(-10) M, the ED50 was 8 X 10(-9) M, and the maximum effect was observed at 5 X 10(-8) M. In contrast, depolarized guinea pig atria were insensitive to A II, Sar1-angiotensin II, and des-Asp1-angiotensin II, even at concentrations as high as 10(-5) M. Rabbit papillary muscle (TTX-blocked), embryonic (18-day) chick heart (partially depolarized) and chick heart reaggregates (TTX-blocked) responded similarly to rabbit atria in that A II (9.6 X 10(-7) M) restored both electrical and mechanical activity. We found that in these preparations the action of A II was unaffected by propranolol (5.0 X 10(-6) M to 5.0 X 10(-5) M) but was blocked by Mn2+ (10(-3) M), D-600 (1 X 10(-7) g/ml) and the specific A II antagonists Sar1-Ala8-angiotensin II (P-113) (5.0 X 10(-5) M) and Sar1-Ile8-angiotensin II (5.28 X 10(-5) M). We conclude that the positive inotropic effect of A II on the myocardium is due to its ability to increase transmembrane ion movements in or through the cell membrane. The ability of Mn2+ and D-600 to block this effect suggests that this ion movement is via the so-called "slow channels."     

Effect of Cerium on Cardiac Muscle of Rat and Guinea Pig

Rare earth elements (REE) have beenused in agriculture widely. But the mechanismof their biological effect is not very clear. REcould antagonize Ca2 in cardiac muslce[1]. Laand Gd could noncompetitively inhibit the ef-feet of Ca2 in cardiac muscular contraction,reduce the activity of adenosine triphosphatasein cardiac sarcoplasm and inhibit the contraction of atria and papillary muscle in guineapig, and cause the visible potential vibration.All these might be caused by the inhibition ofN…     

Canine bronchial sustained contraction in Ca2+-free medium: role of intracellular Ca2+

We evaluated whether cartilage was a source of Ca2+ and the possible role of Ca2+ recycling in the sustained bronchial contraction (SBC) induced by carbachol (Cch) in Ca2+-free medium. Canine first-order bronchi were studied with cartilage and epithelium (+CAR + EPI) and without these structures individually (-CAR + EPI and +CAR - EPI) or together (-CAR - EPI). After cartilage removal (-CAR - EPI or -CAR + EPI) Cch produced a transient contraction in Ca2+-free medium. Removal of the epithelium alone had minor effects on the magnitude of the SBC but increased the effect of removal of cartilage to diminish the SBC. Bronchial strips with cartilage were able to respond to Cch with lower Ca2+ concentrations (10-100 microM) than could dissected preparations. Preincubation with BAY K 8644 (30-1000 nM) or 60 mM KCl or -CAR - EPI tissues converted the transient contractions to Cch in Ca2+-free medium to sustained contractions. In microelectrode studies, 50 nM Cch induced membrane oscillations in solutions with 2.5 mM Ca2+ in bronchial preparations, plus or minus cartilage, and in undissected tissues in Ca2+-free medium but not in -CAR - EPI tissues. Preincubation with 1 microM BAY K 8644 in Ca(2+)-free medium restored these oscillations in -CAR - EPI tissues. The release of 45Ca2+ from cartilage was too rapid to provide a reservoir of Ca2+ to support multiple SBCs in Ca2+-free medium. Moreover, in the Ca2+-free medium (with 10 nM Ca2+ after tissue +CAR + EPI incubation) excitatory junction potentials rapidly disappeared. Addition of 1 microM nifedipine or 1 mM EGTA during the SBC of +CAR + EPI tissues produced complete relaxation. A transient contraction to Cch occurred with prior addition of nifedipine. Inhibition of the sarcoplasmic reticulum Ca2+ pump by tissue incubation with cyclopiazonic acid (CPA; 10 microM), or briefly with 1 mM EGTA significantly diminished the SBC induced by Cch in Ca2+-free medium. CPA and EGTA together abolished the Cch-induced SBC. Thus, cartilage plays a more complex role than as a Ca2+ reservoir to support the SBC induced by Cch in Ca2+-free solution; its removal affects the process supporting SBCs involving intracellular Ca2+ storage and Ca2+ entrance through voltage-dependent channels.     

Effects of semotiadil fumarate (SD-3211) and its enantiomer, SD-3212, on the changes in cytosolic Ca2+ and tension caused by KCl and norepinephrine in isolated rat aortas

Semotiadil fumarate (SD-3211), a Ca2+ channel blocker of benzothiazine derivative and its (S)-(-)-enantiomer (SD-3212), inhibited K(+)- and norepinephrine (NE)-induced contractions in isolated rat aortas. Inhibition of NE contraction induced by both drugs was greater than that induced by diltiazem or bepridil, whereas inhibition of K(+)-contraction was similar to that induced by diltiazem or bepridil. Semotiadil and SD-3212 (10 microM) inhibited the increase in cytosolic Ca2+ ([Ca2+]i) induced by 65.4 mM K+ in fura-2-loaded preparations as well as diltiazem and bepridil (10 microM). On the other hand, semotiadil and SD-3212 (10 microM) inhibited only the early phase of increase in [Ca2+]i induced by 1 microM NE. After 5 min, no significant effect on [Ca2+]i was observed with these compounds despite the significant decrease in the contraction. In contrast to these compounds, diltiazem and bepridil 10 microM affected neither the increase in [Ca2+]i nor the contraction induced by NE. Semotiadil and SD-3212 inhibited the transient contraction induced by 1 microM NE in the absence of external Ca2+. Both compounds partially but significantly inhibited the NE-induced contraction in nifedipine-treated muscles. These results suggest that semotiadil and SD-3212 inhibit contractions of vascular smooth muscle (VSM) not only through blockade of voltage-dependent Ca2+ channels but also through other mechanisms, such as inhibition of Ca2+ release from Ca2+ stores or decrease in sensitivity of the contractile elements to Ca2+.     

Antinociceptive profile of 3-alpha-tropanyl 2-(4-Cl-phenoxy)butyrate (SM-21) [corrected]: a novel analgesic with a presynaptic cholinergic mechanism of action

The antinociceptive effect of (+/-)-3-alpha-tropanyl 2-(4-Cl-phenoxy)butyrate [corrected] (SM-21) (10-40 mg kg(-1) s.c., 10-30 mg kg(-1) i.p., 20-60 mg kg(-1) p.o., 3-20 mg kg(-1) i.v. and 5-20 microg per mouse i.c.v.) was examined in rodents and guinea pigs by using the hot-plate, abdominal constriction, tail-flick and paw-pressure tests. The antinociception produced by (+/-)-SM-21 was prevented by atropine, pirenzepine and hemicholinium-3 but not by quinpirole, R-(alpha)-methylhistamine, [1-[2(methylsufonyl)amino]ethyl]-4-piperidinyl]methyl-5-floro++ +-2-methoxy-1H-indole-3-carboxylate hydrochloride, N6-cyclopentyladenosine, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine hydrobromide, naloxone, 3-aminopropyl-diethoxy-methyl-phosphinic acid or reserpine. On the basis of the above data, it can be postulated that (+/-)-SM-21 exerted an antinociceptive effect mediated by a central potentiation of cholinergic transmission. Affinity profiles of (+/-)-SM-21 for muscarinic receptor subtypes, determined by functional studies (rabbit vas deferens for M1, guinea pig atrium for M2, guinea pig ileum for M3 and immature guinea pig uterus for putative M4) have shown a selectivity ratio M2/M1 of 4.6 that, although very low, might be responsible for the antinociception induced by (+/-)-SM-21 through an increase in ACh extracellular levels. In the antinociceptive dose range, (+/-)-SM-21 did not impair mouse performance evaluated by the rota-rod and hole-board tests.     

Nursing care delivery models in ambulatory oncology

The action of sodium orthovanadate (Na3VO4) on spontaneous mechanical activity of the longitudinal muscle was investigated in isolated segments of rabbit distal ileum. Vanadate (0.3-1000 microM) concentration-dependently enhanced the amplitude of phasic contractions (pendular movements) and caused the muscle tone to slightly increase at the highest concentrations. Both these effects were mimicked by the Ca2+ channel activator BAY K 8644 (10-1000 nM). Vanadate- and BAY K 8644-induced potentiation of mechanical activity was antagonized by the Ca2+ entry blocker nifedipine (3 nM). In Ca(2+)-free, K(+)-depolarized preparations, vanadate (100 microM) failed to contract the musculature, but potentiated the contractile response to applied calcium (CaCl2: 30-300 microM). The action of vanadate was similar to that of BAY K 8644 (3 nM) and was antagonized by nifedipine (0.1 nM). These results suggest that extracellular calcium is required for vanadate-induced smooth muscle excitation which, at least in part, appears to arise from facilitation of calcium influx through voltage-dependent Ca2+ channels.     

Effects of ONO-1101, a novel beta-antagonist, on action potential and membrane currents in cardiac muscle

Direct effects of ONO-1101 ?(-)-[(S)-2,2-dimethyl-1,3-dioxolan-4-yl]methyl-3-[4-[(S) -2-hydroxy-3-(2-morpholino carbonylamino)ethylamino] propoxy]phenylpropionate monohydrochloride), a novel beta-antagonist, on action potential parameters and membrane currents, and its beta adrenoceptor antagonism were examined in cardiac muscle. Action potential-parameters in papillary muscle of reserpinized animals and membrane currents recorded from single myocytes obtained from guinea pig and rabbit hearts were not affected by 1 to 100 microM ONO-1101. On the other hand, ONO-1101 markedly inhibited the potentiation of Ca current by isoproterenol in single cardiac myocytes of the guinea pig. The concentration-response relationship of Ca current for isoproterenol was shifted to the right. This effect resembled that of esmolol, which is also a beta adrenoceptor antagonist. A Schild plot analysis revealed the slope and pA2 value of each antagonist (ONO-1101, 0.94, 8.0; and esmolol, 0.98, 7.3, respectively) and demonstrated that ONO-1101 is about 5 times more potent than esmolol as a beta-antagonist. Two other effects of isoproterenol: 1) potentiation of delayed rectifier K current and 2) activation of chloride current, were also inhibited by ONO-1101. The time required for 50% removal of beta-antagonism of ONO-1101 and esmolol after the washout was estimated as 4 and 6 min, respectively, in depolarized papillary muscle. These results suggest that ONO-1101 is a potent beta-antagonist whose effects were removed quickly by washout. When applied at what is thought to be a clinical dosage, ONO-1101 had no direct effects on action potential-parameters and membrane currents in cardiac muscle. These characteristics of ONO-1101 suggest that this agent may be effective in clinical use.     

Anticonvulsant and adverse effects of MK-801, LY 235959, and GYKI 52466 in combination with Ca2+ channel inhibitors in mice

This study was designed to investigate the influence of the calcium (Ca2+) channel inhibitors nicardipine, nifedipine, and flunarizine on the protective action of MK-801, LY 235959 [N-methyl-D-aspartate (NMDA) receptor antagonists], and GYKI 52466 (a non-NMDA receptor antagonist) against electroconvulsions in mice. Unlike nicardipine (15 mg/kg) or flunarizine (10 mg/kg) nifedipine (7.5 and 15 mg/kg) potentiated the protective potency of MK-801 (0.05 mg/kg), as reflected by significant elevation of the convulsive threshold (a CS50 value of the current strength in mA producing tonic hind limb extension in 50% of the animals). The protective activity of LY 235959 and GYKI 52466 was reflected by their ED50 values in mg/kg, at which the drugs were expected to protect 50% of mice against maximal electroshock-induced tonic extension of the hind limbs. Nicardipine (3.75 15 mg/kg), nifedipine (0.94-15 mg/kg), and flunarizine (2.5-10 mg/kg) in a dose-dependent manner markedly potentiated the antiseizure efficacy of LY 235959. Flunarizine (5 and 10 mg/kg) was the only Ca2+ channel inhibitor to enhance the protective action of GYKI 52466 against electroconvulsions. Except with MK-801 + flunarizine (motor performance) or GYKI 52466 + flunarizine (long-term memory), combination of NMDA or non-NMDA receptor antagonists with Ca2+ channel inhibitors produced an impairment of motor performance (evaluated in the chimney test) and long-term memory acquisition (measured in the passive avoidance task) as compared with vehicle treatment.     

General pharmacological profile of the novel cholecystokinin-A antagonist loxiglumide

The general pharmacological properties of a novel cholecystokinin-A antagonist, loxiglumide ((+/-)-4-(3,4-dichlorobenzamido)-N-(3-methoxypropyl)-N-pentylgl utaramic acid, CR 1505, CAS 107097-80-3) on central nervous system, autonomic nervous system, cardio-respiratory system, gastrointestinal system, hematological and miscellaneous systems were investigated in experimental animals. 1. Central nervous system: At a dose of 30 mg/kg, i.v. loxiglumide showed ptosis in one of 6 mice, but at doses of 3 and 10 mg/kg, i.v. no change on gross behavior in mice. Loxiglumide had no effect on locomotor activity and thiopental-induced hypnosis, anti-convulsive activity, analgesic activity in mice and rectal temperature changes in rats. 2. Autonomic nervous system: In vitro, loxiglumide at concentrations of 10(-4) and 3 x 10(-4) mol/l slightly inhibited agonist-induced contractions in the isolated guinea pig ileum and spontaneous rhythmic contractions in the isolated non-pregnant rat uterus. But loxiglumide had no effect on oxytocin-induced contraction in isolated non-pregnant rat uterus. 3. Cardio-respiratory system: Loxiglumide had no effect on heart rate and electrocardiogram in anesthetized dogs. But it slightly increased blood pressure and decreased the frequency of respirations at a dose of 30 mg/kg, i.v. Furthermore, loxiglumide slightly decreased femoral arterial blood flow at doses of more than 3 mg/kg, i.v. On the other hand, it had no effect on contractile force or contraction rate in the isolated guinea pig atrium and resting tension in the isolated rabbit aorta. 4. Gastrointestinal system: Loxiglumide increased bile secretion at doses of 10 and 30 mg/kg, i.v. in anesthetized rats and at doses of 3, 10 and 30 mg/kg, i.v. in anesthetized dogs. However, total bile acid output was not affected by loxiglumide. On the other hand, loxiglumide had no effect on pancreatic secretion, gastric secretion and gastric emptying in rats and intestinal transport activity in mice. 5. Hematology: In vitro, in the case of samples without bovine serum albumin, at concentrations of more than 1.9 x 10(-3) mol/l loxiglumide showed hemolysis, while in the case of samples with bovine serum albumin, at concentrations of more than 6.9 x 10(-3) mol/l loxiglumide showed hemolysis, and its maximal potency was weak compared to albumin-free conditions. On the other hand, in vivo, loxiglumide had no effect on hemolysis. In addition, it had no effect on platelet aggregation, prothrombin time and activated partial thromboplastin time. 6. Miscellaneous pharmacological actions: Loxiglumide had no effect on local anesthetic activity in guinea pigs and renal function in mice. These results suggest that loxiglumide seems to produce no serious side effects on the central nervous system, autonomic nervous system, cardio-respiratory system, gastrointestinal system, hematological and miscellaneous systems at pharmacologically effective doses.     

Fluoride activates G protein-dependent and -independent pathways in dispersed intestinal smooth muscle cells

The existence of G protein-dependent and -independent mechanisms activated by sodium fluoride was examined in muscle cells isolated separately from the circular and longitudinal layers of guinea pig intestine. The cells were transiently permeabilized by incubation with Trans. Port Reagent in the presence or absence of GDP beta S (100 microM) and then re-sealed. In the absence of GDP beta S, NaF (1 mM) induced contraction and caused an increase in [Ca2+]i, IP3 and diacylglycerol levels and in protein kinase C (PKC) activity in both cell types. In the presence of GDP beta S, the increases in IP3, DAG and PKC were abolished whereas contraction and the increase in [Ca2+]i were partly inhibited. Residual contraction and [Ca2+]i were abolished by the Ca2+ channel blocker, methoxyverapamil. We conclude that contraction and Ca2+ mobilization induced by NaF is mediated by G protein activation as well as by a G protein-independent mechanism involving activation of plasmalemmal Ca2+ channels.