Characterization and mediation of inhibitory junction potentials from opossum lower esophageal sphincter

BACKGROUND: Activating nonadrenergic, noncholinergic (NANC) nerves of the lower esophageal sphincter (LES) hyperpolarizes and relaxes its circular smooth muscle. This relaxation is mediated by nitric oxide (NO) or an NO-containing compound. These studies were undertaken to compare the electrophysiological responses of circular smooth muscle from the LES and esophagus in response to NANC nerve stimulation and to test the hypothesis that NO mediates LES hyperpolarization. METHODS: The transmembrane potential difference was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by electrical pulses of 0.5 msec duration and 50 V amplitude. RESULTS: Responses of LES muscle differed from those of the esophageal muscle. The duration of hyperpolarization was much longer in sphincteric muscle. The depolarization that followed hyperpolarization of esophageal muscle was not observed in sphincteric muscle. NG-nitro-L-arginine, an inhibitor of NO synthase, attenuated the nerve-induced hyperpolarization. L-arginine, the substrate for NO synthase, antagonized the effect of NG-nitro-L-arginine. Exogenous NO hyperpolarized of the smooth muscle membrane. CONCLUSIONS: These data support the hypothesis that NO or an NO-like compound may mediate nerve-induced hyperpolarization of the opossum LES.     

Different protein kinase C isozymes mediate lower esophageal sphincter tone and phasic contraction of esophageal circular smooth muscle

Circular muscle of the esophagus (ESO) is normally relaxed and contracts phasically in response to neural stimuli. In contrast, lower esophageal sphincter (LES) circular muscle maintains spontaneous tone and relaxes in response to neural stimuli. We have previously shown that in vitro, spontaneous LES tone and contraction of ESO in response to acetylcholine (ACh) are antagonized by protein kinase C (PKC) inhibitors, suggesting that PKC activation is responsible for these functions. In the current study, Western blot analysis of LES and ESO revealed PKC-alpha, -betaII, and -gamma isozymes in LES circular muscle, but only PKC-betaII translocated from the cytosolic to the membrane fraction in response to ACh. In contrast, ESO contained PKC-betaII, -gamma, and -epsilon, and only PKC-epsilon translocated to the membrane fraction in response to ACh. In LES single cells isolated by enzymatic digestion and permeabilized by saponin, 1-2-dioctanoylglycerol-mediated contraction was inhibited by preincubation with PKC-betaII antiserum but not by other PKC antisera. In esophageal cells, contraction was inhibited by the PKC-epsilon antiserum but not by antisera against other PKC isozymes. N-Myristoylated peptides derived from the pseudosubstrate sequences of PKC isozymes were used to inhibit saponin, 1-2-dioctanoylglycerol-induced contraction of LES and ESO smooth muscle cells. Contraction of LES cells was reduced by the alpha beta gamma pseudosubstrate but not by the alpha, delta, or epsilon pseudosubstrate. Contraction of ESO cells was reduced by the epsilon pseudosubstrate but not by the alpha, delta, or alpha beta gamma pseudosubstrate. We conclude that different types of contractile activity in the ESO and LES are mediated by different PKC isozymes. LES contraction is mediated by the calcium-dependent PKC-betaII, whereas contraction of ESO is mediated by the calcium-independent PKC-epsilon.     

Alteration by phosphatidyl serine of tension responses and 45Ca distribution in aortic smooth muscle

The effects of phosphatidyl serine (PS) on 45Ca distribution, 45Ca movements and contractions were examined in rabbit aortic smooth muscle. Contractile responses to submaximal concentrations of norepinephrine and histamine were potentiated by prior exposure to PS, but equivalent responses to potassium were unaffected. Addition of PS to the incubation solution decreased 45Ca uptake; exposure of aortic strips to PS during washout of either 45Ca or promethium (147Pm) resulted in maintained increases in efflux. These PS-induced alterations in net loss of 45Ca or 147Pm can be attributed to a decreased membrane reuptake and/or rebinding. However, the presence of PS during the washout significantly reduced the increases in 45Ca efflux rate elicited with either 0.05 mM concentrations of Ca++ or ethylenediamine tetraacetic acid. Thus, in rabbit aortic smooth muscle, exogenous PS can alter the availability and/or exchangeability of a membrane-bound Ca++ fraction. By specifically increasing the affinity for Ca++ at relevant membrane sites or stores. PS may enhance the ability of vascular smooth muscle to respond to stimulatory agents that mobilize Ca++ from these sites and, in this manner, potentiate contractile responses.     

Ethical review of multi-centre research: a survey of local research ethics committees in the south Thames region

We reported a 63-year-old woman with myotonic dystrophy (MD), who had frequent swallowing disturbances and died from suffocation asphyxia. Her esophagus on CT image 30 minutes after taking semi-solid meal showed dietary remnants in the middle portion of esophagus with entire esophageal dilatation. At autopsy, there was marked atrophy in the striated muscles in the upper part and smooth muscles in the lower part of the esophagus. The site of dietary stagnation on CT image was identical to the atrophic smooth muscle layer seen at autopsy. We speculate that one of the causes of esophageal motor dysfunctions is smooth muscle atrophy. The dietary stagnation in the esophagus may increase a risk of the asphyxia. Therefore we need to keep patients at the straight position during and after dietary ingestion to prevent respiratory problems.     

Influences of Mg++ and reserpine on calcium fluxes and sensitivity of the rat aorta

Rat aorta became supersensitive and subsensitive to noradrenaline (NA), respectively, in Mg++-free and 3.6 mM Mg++ media reserpine treatment reduced the sensitivity in normal or high (3.6 mM) Mg++ media but had no effect in Mg++-free medium. Incubation of aortae in Mg++-free medium enchanced 45Ca++ uptake and efflux in rat aorta, whereas, it reduced 45Ca++ efflux without a change in 45Ca++ uptake by rabbit aorta. Reserpine pretreatment enhanced 45Ca++ efflux from rat aorta without a changed in 45Ca++ uptake in normal Mg++-free medium. Unlike in rat aorta, reserpine enhanced 45Ca++ uptake by and reduced efflux from rabbit aorta in Mg++-free medium but not in normal medium. These results suggest that the failure of reserpine to induce supersensitivity in rat aorta to NA may be due to poor capacity of the muscle to retain Ca++ and probably also due to an enhanced antagonism of Mg++ on Ca++ movements.     

Effect of cholecystokinin-octapeptide on lower esophageal sphincter

The effect of cholecystokinin-octapeptide (CCK-OP) on the lower esophageal sphincter (LES) was studied in 50 cats in vivo. CCK-OP caused a dose-dependent fall in LES pressures in all but 4 animals. Maximal sphincter relaxation was obtained with 200 to 400 ng of CCK-OP per kg of body weight. Atropine sulfate and/or hexamethonium, or adrenergic blocking agents (phentolamine or propranolol), in doses that completely inhibit the action of maximal doses of their respective agonists, failed to block the CCK-OP effect. Tetrodotoxin, however, in doses that denervates the LES, antagonized the CCK-OP-induced sphincter relaxation. In these tetrodotoxin-treated animals, CCK-OP produced LES contraction similar to that observed after pentagastrin. These results suggest that CCK-OP stimulates the postganglionic nonadrenergic, noncholinergic inhibitory neurons responsible for sphincter relaxation. CCK-OP also stimulates the circular muscle by direct action causing LES contraction. The latter becomes apparent when the innervation of the LES is abolished by tetrodoxtin.     

Mechanism of action of metoclopramide on opossum lower esophageal sphincter muscle

The purpose of this study was to investigate the mechanism of action of metoclopramide on the lower esophageal sphincter (LES) muscle of the opossum. Metoclopramide gave a dose-related increase in LES muscle active tension. A peak response of 12.5 +/- 2.1 g (mean +/- SEM) was achieved at 3.1 X 10(-4) M. The maximal and submaximal LES muscle response to metoclopramide could not be antagonized by atropine, hyoscine, hexamethonium, tetrodotoxin, phentolamine, diphenhydramine, or propranolol. Metoclopramide did not augment the submaximal muscle responses to gastrin I, acetylcholine, or norepinephrine. These studies suggest that in the opossum, metoclopramide acts through a direct action on the smooth muscle.     

Muscular composition of the gastric groove in the golden hamster

The golden hamster possesses a forestomach and a glandular stomach. The gastric groove connects the cardia to the glandular stomach and is situated on the lesser curvature of the stomach. The constitution of the muscle fibers in the gastric groove was investigated. The gastric groove consisted of two lips and a groove floor. The muscle coat of the lips was composed of a mixture of smooth and striated muscle fibers. The smooth muscle fibers were components of the cardiac muscle loop. The striated muscle fibers were extensions from the esophageal inner circular muscle layer, and invaded about half the length of the lips. The muscle coat of the groove floor consisted of an inner circular muscle layer made up of smooth muscle fibers, and the outer longitudinal muscle layer of the striated muscle fibers extended from the esophageal outer longitudinal muscle layer. The present study revealed that the muscle coat of the gastric groove in the golden hamster was composed of smooth and striated muscle fibers, and that these striated muscle fibers were extensions of the esophageal muscle coat.     

Should adjuvant or neoadjuvant treatment be administered in esophageal cancer?

The Nissen fundoplication is not the proper antireflux procedure for patients with poor esophageal peristalsis as it does not strengthen impaired esophageal peristalsis. The aim of this study was to investigate if tailoring of antireflux surgery according to esophageal contractility is an effective treatment of gastroesophageal reflux disease (GERD) with a low incidence of postoperative dysphagia. The Toupet fundoplication was laparoscopically performed on 32 patients with poor esophageal peristalsis and the Nissen fundoplication on 17 patients with normal peristalsis. After a median follow-up of 15 months, only 1 of the 49 patients (2.04%) complained of heartburn. Acute esophagitis was found in none of them on endoscopy. Of 40 patients tested postoperatively, 2 (5%) underwent pathologic esophageal pH monitoring. Postoperative dysphagia was found in two patients (4.1%) compared with 25 (51%) preoperatively (p < 0.05). There was a significant reduction of dysphagia following the Toupet fundoplication. Both procedures increased the resting pressure of the lower esophageal sphincter (LES) significantly, which was more pronounced following the Nissen fundoplication. Relaxation of the LES was significantly better following the Toupet than after the Nissen fundoplication. There was significant improvement of esophageal peristalsis following the Toupet fundoplication. Tailored antireflux surgery is an effective strategy for treatment of GERD. The incidence of postoperative dysphagia is low owing to improvement of impaired esophageal peristalsis following the Toupet fundoplication. It may be due to the fact that the Toupet fundoplication causes less esophageal outflow resistance than the Nissen fundoplication.     

Multiple channels mediate calcium leakage in the A7r5 smooth muscle-derived cell line

Ca2+ entry under resting conditions may be important for contraction of vascular smooth muscle, but little is known about the mechanisms involved. Ca2+ leakage was studied in the A7r5 smooth muscle-derived cell line by patch-clamp techniques. Two channels that could mediate calcium influx at resting membrane potentials were characterized. In 110 mM Ba2+, one channel had a slope conductance of 6.0 +/- 0.6 pS and an extrapolated reversal potential of +41 +/- 13 mV (mean +/- SD, n = 8). The current rectified strongly, with no detectable outward current, even at +90 mV. Channel gating was voltage independent. A second type of channel had a linear current-voltage relationship, a slope conductance of 17.0 +/- 3.2 pS, and a reversal potential of +7 +/- 4 mV (n = 9). The open probability increased e-fold per 44 +/- 10 mV depolarization (n = 5). Both channels were also observed in 110 mM Ca2+. Noise analysis of whole-cell currents indicates that approximately 100 6-pS channels and 30 17-pS channels are open per cell. These 6-pS and 17-pS channels may contribute to resting calcium entry in vascular smooth muscle cells.     

Coordination of peristalsis in pharynx and esophagus

When a swallowed liquid bolus is followed from mouth to stomach in man by contrast studies or manometry, it traverses its course without hesitation even though the bolus is propelled by striated muscle contraction in the first part of its journey and smooth muscle in the latter part. The striated muscle is innervated by excitatory cholinergic nicotinic cranial nerves whereas the smooth muscle of the esophagus is innervated by the enteric nervous system (ENS) through excitatory and inhibitory nerves. These differences can be demonstrated by observing the inhibitory effects of curare and atropine, the first blocking nicotinic receptors and the second muscarinic receptors. Early students of esophageal motility recognized that peristalsis could be initiated in two ways. The first is initiated by a swallow and is called primary peristalsis and the second called secondary peristalsis is initiated by distension of the esophagus. It was proposed that primary peristalsis was initiated by a single sensory input activated by the bolus entering the pharynx which in turn activated a motor program in the brain stem. Secondary peristalsis was believed to be stimulated by multiple afferent impulses arriving from the esophagus as the bolus passed down the esophagus. More recent studies using manometric techniques have suggested that the only difference between primary and secondary peristalsis is the afferent stimuli and the effector mechanism is the same. Subsequent studies of carefully timed, paired swallows, transection of vagus nerves and esophagus, and single nerve recordings suggest that the answer lies between the two extremes noted above.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coupling of store-operated Ca++ entry to contraction in rat aorta

The purpose of this study was to test whether the elevated intracellular Ca++ level ([Ca++]i) resulting from store-operated Ca++ entry was associated with vascular smooth muscle contraction. Cyclopiazonic acid (CPA), a selective inhibitor of sarcoplasmic reticulum Ca(++)-ATPase, concentration-dependently (1-10 microM) elevated [Ca++]i in rat aorta, as indicated by an increase in the fura-2 340/380 ratio. Simultaneous measurement of contraction demonstrated that 1 and 10 microM CPA induced insignificant and variable amounts of contraction, respectively. Verapamil (10 microM) had relatively little effect on the 1 and 10 microM CPA-elevated [Ca++]i. In contrast, Ni++ (0.1 mM), in the presence of verapamil, abolished the 1 microM CPA-elevated [Ca++]i. Ni++ (0.1 mM) also partially decreased the 10 microM CPA-elevated [Ca++]i and, furthermore, abolished the associated contraction. A higher Ni++ concentration (1 mM) abolished the 10 microM CPA-elevated [Ca++]i that remained after verapamil and 0.1 mM Ni++. Phorbol dibutyrate (10 nM), a protein kinase C activator, potentiated contractions to 1 and 10 microM CPA in the presence of verapamil. Ni++ (0.1 mM) abolished the enhanced contractions, and decreased the elevated [Ca++]i. These results suggest that 1) elevated [Ca++]i due to store-operated Ca++ entry is dissociated from contraction; 2) the elevated [Ca++]i is restricted to at least two noncontractile compartments that can be differentiated by their relative sensitivities to blockade by low (0.1 mM) and higher (1 mM) Ni++ concentrations, and 3) [Ca++]i elevation within the compartment sensitive to blockade by 0.1 mM Ni++ can be coupled to contraction via protein kinase C activation.     

Interaction between calponin and smooth muscle myosin

Calponin is a thin filament-associated protein in smooth muscle that has been shown to bind actin, tropomyosin and calmodulin, and has been implicated to play a role in regulation of smooth muscle contractility. Using a centrifugation assay we found that calponin interacts with unphosphorylated filamentous smooth muscle myosin. We found that this calponin-myosin interaction is reversed by Ca(2+)-CaM, and depends on ionic strength. At 50 mM NaCl the binding constant and the stoichiometry of this interaction were estimated to be 2 x 10(6) M-1, and 1.2-2.4 calponin per myosin, respectively. We suggest that the calponin-myosin interaction could be involved in regulation of smooth muscle contractility by anchoring myosin to actin.     

Enhancement of Ca++ uptake by lactose in the rat small intestine

In previous experiments, lactose was shown to increase the absorption of Ca++ by the small intestine of the rat and other mammals. To further investigate the mechanism of the lactose effect, Ca++ uptake was studied in everted gut sac preparations. Gut sacs from the rat ileum were preincubated with or without lactose for 45 minutes, and then the tissue uptake of 45Ca over the first 3 minutes was measured in the presence or absence of lactose. The presence of 160 mM lactose increased the initial rate of Ca++ uptake in the first minute by 64% compared to the NaCl control. The lactose effect was dependent on the presence of lactose in the preincubation medium only and not on the presence of lactose during the measurement of Ca++ uptake. Lactose increased Ca++ absorption when the Ca++ concentrations ranged from 0.1 to 10 mM. However, the magnitude of the enhancement was dependent on the lactose concentration and was reduced below 160 mM lactose. When Ca++ and lactose uptake during a 45 minute period was measured in parallel experiments, no evidence for the co-transport of lactose and Ca++ into the tissue was found. These and other data indicated that lactose is not interacting directly with Ca++ in solution but is interacting with the absorptive cells of the intestine to increase their permeability to Ca++.     

Contraction and resting stiffness of isolated cardiac muscle: effects of inotropic agents

The purpose of this study was to test the hypothesis that either hypoxia and its combined effects with extracellular calcium (Ca), digoxin, and ouabain, or these positive inotropic agents acting alone or in combination, influence contraction and resting stiffness of isolated papillary muscle. Stiffness was measured utilizing the sinusoidal forcing function technique. Neither an increase in extracellular calcium concentration (from 2.5 to 4.0 mM) nor digoxin or ouabain in either Ca concentration altered contraction or resting stiffness in the well-oxygenated environment. Resting stiffness for any given resting tension was increased at the end of hypoxia only in the presence of digoxin, and this occurred in both 2.5 mM Ca (P less than 0.02) and in 4.0 mM Ca (P = 0.05). Contraction stiffness for any given tension was increased in 2.5 mM Ca by hypoxia alone (P less than 0.05) and by hypoxia in the presence of digoxin (P less than 0.005) and ouabain (P less than 0.02), but was not increased in any experiments conducted in 4.0 mM Ca. The conclusions from these data are that certain experimental conditions of the study evoked different directional changes in stiffness and contractility. Further, changes in contraction stiffness are not always paralleled by changes in resting stiffness.     

Vasodilative response to hypoxia and simulated ischemia is mediated by ATP-sensitive K+ channels in guinea pig thoracic aorta

Local vasodilation in response to hypoxia or ischemia improves perfusion and O2 supply of the affected tissue. This local vasodilation thus constitutes the most important mechanism in the prevention of ischemic cell injury. The regulation of vascular tone has mainly been attributed to changes of cytoplasmatic Ca2+ ((Ca2+)i) concentrations in vascular smooth muscle cells. The mechanism underlying these changes has not, however, been elucidated so far. Using aortic strips of guinea pigs (transversally cut in spirals; normal Tyrode, in mM: NaCl 150, KCl 4.5, MgCl2 2, CaCl2 2.5, glucose 10; buffered with 10 mM HEPES at pH 7.4; equilibrated with 100% O2 at 31 degrees C) the authors could show that metabolic blockade (glucose replaced by 10 mM 2-deoxyglucose (DOG) led to a relaxation of the preparation. Thus, in four experiments, resting tension decreased from 0.75 g by 27% +/- 12% within two hours (% of maximal contractile force developed by each preparation when depolarized with 43 mM KCl and 101.5 mM NaCl). When the same experiment was carried out in the presence of 1 mM tolbutamide (a known blocker of ATP-dependent K+ channels) in vascular smooth muscle no such relaxation could be seen (n = 4). Furthermore, in the same type of preparation, similar results have been obtained upon hypoxic relaxation (100% O2 replaced by 100% N2), where 1 mM tolbutamide also prevented vasodilation. Thus, hypoxic/ischemic vasodilation in response to glycolytic inhibition (DOG) and hypoxia (N2) is based upon the opening of K+ ATP channels and hence can be prevented by sulfonylureas (the opening of K+ ATP channels would lead to hyperpolarization (increased K+ conductance, Goldmann equation), thus diminishing the open probability of voltage-gated Ca2+ channels with subsequent vasodilation). This inhibition by sulfonylureas of vasodilative response to ischemia may also constitute the so far unknown cause of the increased cardiovascular mortality seen under sulfonylurea treatment.     

The difference in the inhibitory mechanisms of papaverine on vascular and intestinal smooth muscles

Papaverine (0.3-100 microM) more potently inhibited phenylephrine (1 microM)-induced contraction than 65 mM K+-induced contraction of the aorta, while it equally inhibited contractions induced by 65 mM K+ and carbachol (1 microM) in ileal smooth muscle. In phenylephrine-treated aorta, papaverine (1-10 microM) increased the cAMP and cGMP content. However, in carbachol-treated ileum, 30 microM papaverine partially increased the cAMP content while it maximally relaxed the preparation. In fura2-loaded aorta, papaverine (0.3-10 microM) inhibited both the contraction and the increase in intracellular Ca2+ level ([Ca2+]i) induced by phenylephrine in parallel. However, papaverine inhibited carbachol-induced contraction with only a small decrease in [Ca2+]i. Papaverine (1-30 microM) inhibited the carbachol-induced increase in oxidized flavoproteins, an indicator of increased mitochondrial oxidative phosphorylation, in ileal smooth muscle whereas it did not change the phenylephrine-induced increase in the aorta. These results suggest that papaverine inhibits smooth muscle contraction mainly by the accumulation of cAMP and/or cGMP due to the inhibition of phosphodiesterase in the aorta whereas, in ileal smooth muscle, papaverine inhibits smooth muscle contraction mainly by the inhibition of mitochondrial respiration.     

Thoracoscopic surgery for benign esophageal diseases

The thoracoscopic surgery for two benign esophageal diseases, esophageal leiomyoma and esophageal diverticulum, were successfully performed. Case 1 was a 37-year-old female with esophageal leiomyoma that was located at 30 cm from the incisor of the left anterior esophagus. The tumor was enucleated under the thoracoscopy, combined mini-thoracotomy for 3 cm in length. It was useful enough to rotate the left side to the right with two slings traction for better visualization of lesion site. After resection, the proper muscle layer of the esophagus was closed. Case 2 was a 70-year-old male, who complained of dysphagia because of esophageal diverticulum. It was 8 cm in size and located at 28 cm from the incisor of the right wall of the esophagus. It was also resected under the thoracoscopy, combined mini-thoracotomy for 3 cm in length. Intraluminal esophagoscope was useful to dissect safely and confirm the intralumen of the diverticulum. Its neck was divided parallel to the longitudinal axis of the esophagus by two endo-staplers. And then, the muscle layer was closed. It was suggested that esophageal leiomyoma and esophageal diverticulum were suitable for thoracoscopic surgery.     

Effect of motilin on the lower esophageal sphincter of the opossum

We have studied the effect of Yajima's synthetic motilin on the lower esophageal sphincter (LES) of the opossum and compared its potency to that of gastrin and its interaction with secretin. Dose-response curves for the LES were constructed from the intravenous bolus injection of graded doses of motilin and gastrin alone and motilin given against a background infusion of secretin. The smallest dose of motilin that elicited a significant response was 0.05 microng/kg, and the highest response was observed with the highest dose used in this study (1.0 microng/kg). Over a wide dose range, both motilin and gastrin were found to be equally potent in stimulating the LES of the opposum, and secretin caused inhibition of the LES pressure to motilin. Therefore, we conclude that (1) motilin is a potent stimulant of the LES; (2) this response is dose dependent; (3) motilin's potency is similar to that of gastrin; and (4) secretin counteracts the effect of motilin on the LES.     

Reversal of somatostatin inhibition of insulin and glucagon secretion

These studies were designed to elucidate the mechanism of inhibitory action of somatostatin (SRIF) on glucagon (IRG) and insulin (IRI) secretion. Studies were carried out in the unrecirculated isolated rat pancreas perfusion with arginine 19.2 mM and glucose 5.5 mM as stimulus primarily for IRG but also IRI secretion. The effects of excess Ca++ (15.2 mEq./L.) and excess K+ (12.8 mEq./L.) on IRG, IRI, and the SRIF-inhibited pancreas were studied. Ca++ excess in five perfusions strikingly stimulated IRG secretion (+92 per cent) but only stabilized IRI secretion compared with control perfusions. K+ excess (in seven perfusions) markedly inhibited IRG secretion (-39 per cent) while stimulating IRI secretion (+16 per cent). Restoration of normal concentrations of K+ resulted in a rebound of IRG to levels 120 per cent that of controls. SRIF, at concentrations from 0.1-20 ng./ml., produced inhibition of both IRG and IRI. In 11 perfusions, with SRIF at 10 ng./ml., IRG decreased more than IRI (-75.2 per cent IRG and -46.9 per cent IRI). In five perfusions, addition of Ca++ (15.2 mEq./L.) 10 minutes after SRIF was started resulted in a reversal of IRG inhibition to 69.4 per cent and IRI to 73.2 per cent of the arginine controls. The reversal by Ca++ of SRIF effect on IRG was greater at higher concentrations of Ca++, suggesting some form of competition. In four perfusions, excess K+ reversed SRIF-induced IRI inhibition to 79.6 per cent that of controls but had no effect on IRG inhibition. Studies in vitro with isolated islets revealed that SRIF (2 mug./ml.) inhibited 45Ca uptake of islets as did epinephrine (10(-5) M). It was concluded that SRIF-induced inhibition of hormone release appears related to an action on Ca++ uptake.