Changes in myosin expression in denervated laryngeal muscle

The effects of chronic denervation on the myosin heavy chain (MyHC) content and muscle fiber type composition of rat laryngeal muscles are described. The posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were removed 3 weeks, 3 months, and 6 months after recurrent laryngeal nerve sectioning. Myofibrillar adenosine triphosphatase staining of cryostat sections was performed, and fiber type percentages were determined. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to separate MyHC isoforms, and densitometry was subsequently used for quantitative analysis. Unoperated animals served as controls. In the PCA muscle, denervation resulted in a progressive reduction in type I MyHC (the slow-contracting isoform) to an almost complete loss at 6 months, with a concomitant increase in type II MyHCs (fast-contracting isoforms, excluding type IIL). Type IIL MyHC (laryngeal-specific isoform) remained relatively constant up to 6 months after denervation. The myosin expression in the TA muscle, which contained only type II MyHCs, remained relatively constant with denervation. Changes in fiber type composition of the muscles described from tissue staining correlated with MyHC content. These findings in laryngeal muscle confirm the dependence of type I MyHC expression upon neural input, as has been found previously in limb skeletal muscles. Since the expression of all MyHCs except the IIL was modified after denervation in the PCA muscle, it is possible that the IIL isoform is maintained by factors that differ from those in the other skeletal myosins.     

Role of Na+/H+ exchange in the recovery of contractility during hypercapnia in cat papillary muscles

Cholesterol reduction reduces ischaemic cardiovascular morbidity and mortality in the asymptomatic healthy population as well as in those with known coronary artery disease. Angiographic studies have also demonstrated regression of atherosclerotic plaques as well as retardation of new atheroma formation with such therapy. Yet, there is a consistent inability to reduce overall mortality in cholesterol-lowering drug trials. An excess of suicide, homicide and violence has been attributed to cholesterol reduction interfering with membrane lipids and receptors, leading to aggressive behaviour. The risk and benefits of cholesterol reduction must thus be weighed in the individual patient; it is more useful in those with known coronary artery disease who are at high risk of subsequent ischaemic cardiovascular events.     

Changes in muscle blood flow distribution during hyperthermia

Blood flow is a critical parameter for obtaining satisfactory temperature distributions during clinical hyperthermia. This study examines the changes in blood flow distribution in normal porcine skeletal muscle before, during and after a period of regional microwave hyperthermia. The baseline blood flow distribution during general anaesthesia and after the insertion of the thermal probes was established independently in order to isolate the changes due to hyperthermia. General anaesthesia alone and thermocouple insertion during anesthesia had no significant effect on the muscle blood flow distribution. Regional microwave heating generated a non-uniform blood flow distribution which was a function of the tissue temperature distribution. Blood flow was greater in those tissues samples in which higher temperatures were recorded and less in those sampled further from the applicators peak SAR (Specific Absorption Rate). The increase in blood flow appears to be primarily a local phenomenon. Although muscle blood flow may be considered to be uniform prior to heating, this does not hold during hyperthermia treatment. Therefore, the non-uniform nature of the blood distribution during heating should be incorporated into any practical bioheat transfer model.     

Control of transmission in muscle group IA afferents during fictive locomotion in the cat

1. Primary afferent depolarization (PAD) can be evoked by sensory volleys, supraspinal commands, or the activity of spinal locomotor networks (locomotor-related PAD). In this study we investigated the effect of locomotor-related PAD and of sensory-evoked PAD on the monosynaptic transmission between the group IA muscle afferents and motoneurons in the lumbosacral spinal cord. 2. Six pairs of group IA afferents and motoneurons [4 tibialis anterior (TA), 1 medial gastrocnemius (MG), 1 lateral gastrocnemius-soleus (LGS)] were successfully recorded intracellularly during spontaneous fictive locomotion in the decerebrate cat. The membrane potentials of TA axons and motoneurons were maximally depolarized during the flexor phase of the locomotor cycle. In MG and LGS pairs, the maximum depolarization in IA axons occurred during the flexor phase and, in motoneurons, during the extensor phase. There were no antidromic discharges in the recorded axons. The effects of locomotor-related PAD on IA transmission were evaluated by comparing the unitary excitatory postsynaptic potentials (EPSPs) in the motoneuron evoked by the spontaneous orthodromic firing of the group IA axon during the flexor and extensor phases, respectively. In TA pairs, the maximum amplitude of unitary EPSPs occurred during the flexor phase when the motoneuron and the axon were maximally depolarized. In the MG and LGS pairs, the maximal amplitude of unitary EPSPs occurred during the extensor phase when the motoneuron was maximally depolarized and when the axon was the least depolarized. Overall, the amplitude of unitary EPSPs was clearly modulated during the fictive step cycle and always reached a maximum during the depolarized phase of the motoneuron, whether the group IA axon was maximally depolarized or not during that phase. 3. The effect of sensory-evoked PAD on synaptic transmission was also studied in nonlocomoting preparations. One TA pair was successfully recorded and PADs were evoked by the stimulation of a peripheral nerve. The amplitude of unitary EPSPs in the motoneuron was greatly depressed during the PADs. This result is a direct demonstration of the presynaptic inhibition associated with the sensory-evoked PAD in the monosynaptic reflex pathway of the cat. 4. We conclude from these results that the locomotor-related PAD did not contribute significantly to the modulation of transmission in the monosynaptic reflex pathway of the cat during fictive locomotion. On the other hand, the results confirmed that PAD evoked by sensory input decreases group IA afferent transmission efficiently most probably by presynaptic inhibition. The results suggest therefore that, during real locomotion, sensory feedback induced by the moving limbs or perturbations will evoke an important presynaptic inhibition of the release from group IA primary afferent terminals.     

Labelled decamethonium in cat muscle

1 Tritium-labelled decamethonium was infused intravenously in 12 cats at final rates of 1.3-4.2 nmol kg-1 min-1 to produce a steady plasma concentration which ranged between 0.21-1.3 mumol/l in different experiments. Muscle contractions were elicited by nerve stimulation and the potential at the end-plate regions of superficial fibres was recorded by extracellular electrodes. 2 Under these conditions, it was not possible to obtain a steady degree of neuromuscular block. The initial decrease in muscle contractions was followed by recovery towards the original value although the concentration of decamethonium in the plasma remained constant, or in some cases rose. The initial depolarization of the end-plate region also waned during the constant infusion of the drug. 3 Once the twitch tension had returned to control values during infusion of the drug, prolongation of the infusion for a total of four hours did not produce a secondary neuromuscular block. 4 Scintillation counting showed that during infusion of labelled decamethonium the radioactivity of the muscles increased progressively with time. The uptake was less in the soleus muscle than in the fast-contracting flexor longus digitorum and extensor longus digitorum muscles. Muscles which had been denervated 12-13 days previously showed a greater uptake of labelled drug than control muscles from the contralateral limb. 5 The labelled drug was localized by autoradiography of frozen sections of leg muscles following intra-arterial injection of decamethonium. Grain counts in individual fibres showed that small amounts of decamethonium had entered the muscle fibres along their entire length, and there was increased uptake of the drug into the cell in the region of the end-plate. 6 The mechanisms underlying the waning of the pharmacological response during constant application of depolarizing drugs are discussed.     

Doublet potentiation during eccentric and concentric contractions of cat soleus muscle

The addition of an extra stimulus pulse, or doublet, at the beginning of a low-frequency train has been shown to substantially increase isometric force. This study examined the effects of muscle movement on this doublet potentiation. The soleus muscles of anesthetized cats were stimulated at 10 Hz for 1 s, with and without an added doublet (0.01-s interval). Isovelocity releases reduced but did not eliminate peak and early doublet potentiation (average 0.0-0.5 s after the doublet). Large releases, >0.4 s after the doublet, completely abolished sustained doublet potentiation (average 0.5-1.0 s after the doublet). In contrast, early isovelocity stretches boosted peak doublet potentiation. Yet, large stretches later in the stimulus almost completely eliminated sustained doublet potentiation. This suggests that a different mechanism is responsible for early and sustained doublet potentiations. Because peak and average initial doublet potentiation were not strongly affected by movement, doublets still offer a viable control strategy to increase force during movement while minimizing the number of stimulus pulses.     

Correlation of laryngeal chemoreflex severity with laryngeal muscle response

Posterior patterning in the Drosophila embryo requires the action of Nanos (Nos) and Pumilio (Pum), which collaborate to regulate the translation of maternal hunchback (hb) mRNA. Previous work demonstrated that Pum recognizes sites in the 3' UTR of hb mRNA. In this report, we first define the RNA-binding domain of Pum and then show that residues essential for translational repression are embedded within this domain. We also show that Nos and Pum can repress cap-independent translation from an internal ribosome entry site (IRES) in vivo, suggesting that they act downstream of the initial steps of normal, cap-dependent translation.     

Changes in the calpains and calpastatin during postmortem storage of bovine muscle

Changes in activity and protein status of micro-calpain, m-calpain, and calpastatin in bovine semimembranosus muscle during the first 7d of postmortem storage were monitored by using assays of proteolytic activity, SDS-polyacrylamide gel electrophoresis, and Western blot analysis. Extractable m-calpain activity changed slightly during the first 7d after death (decreased to 63% of at-death activity after 7d), whereas extractable calpastatin activity decreased substantially (to 60% of at-death activity after 1d and to 30% of at-death activity after 7d of postmortem storage) during this period. Extractable micro-calpain activity also decreased rapidly (to 20% of at-death activity at 1d and to less than 4% of its at-death activity at 7d after death) during postmortem storage. Western blot analysis showed that the 80-kDa subunit of m-calpain remained undegraded during the first 7d after death but that the 125- to 130-kDa calpastatin polypeptide was gone entirely at 7d after death. Hence, the calpastatin activity remaining at 7d originates from calpastatin polypeptides that are 42 kDa or smaller. The 80-kDa micro-calpain subunit was almost entirely in the 76-kDa autolyzed form at 7d after death; this form is proteolytically active in in vitro systems, and it is unclear why the postmortem, autolyzed micro-calpain is not active. Over 50% of total muscle micro-calpain is tightly bound to myofibrils 7d after death; this micro-calpain is also nearly inactive proteolytically. Unless postmortem muscle contains some factor that enables micro-calpain in this muscle to be proteolytically active, it is not clear whether micro-calpain could be responsible for any appreciable postmortem myofibrillar proteolysis.     

Changes in vacuolar protease activities during synchronous culture of Saccharomyces cerevisiae

Enzymatic activities of proteinases A and B, carboxypeptidase Y, and aminopeptidase I, vacuolar enzymes in beer yeast, Saccharomyces cerevisiae, were measured at different stages of growth in the synchronous culture. All enzymatic activities fluctuated synchronously during the cell growth in a periodical cycle. The maximum activities were observed before cytokinesis and the minimum activities were found just after completing cytokinesis.     

Changes in fusimotor activity during repetitive lengthening muscle contractions in decerebrate cats

The purpose of this study was to determine whether enzymatic and histochemical characteristics of human skeletal muscle are altered with aging. Tissues from the vastus lateralis (VL) and gastrocnemius were analyzed for citrate synthase (CS) activity and fiber type in 55 sedentary men (age range 18-80 yr). In this population, CS activity in the gastrocnemius was negatively related to age (r = -0. 32, P < 0.05); there was no relationship in the VL. Treadmill-determined maximal oxygen consumption was positively related (r = 0.40, P < 0.05) to CS in the gastrocnemius but not in the VL. CS activity in the gastrocnemius was 24% lower in the oldest (>/=60 yr, n = 10) vs. the youngest (相似文献   

Functional alterations in the pulmonary respiratory system in dogs during alveolar hypoxia with hypercapnia

In acute experiments on 25 dogs, interrelationships of parameters of the small circulation, ventilation, and diffusion were studied during alveolar hypoxia with hypercapnia. Two types of responses of the lung breathing system were revealed. The 1st one involved an increase of the small circulation pressure (by 84%), of volume blood flow (by 42%), of the lung blood volume (by 24%), and of the lung diffusion ability (by 47%). The 2nd type of responses involved an increase of the small circulation pressure on the average by 70%, while the other three parameters practically did not change at all. The combined action of such hemodynamic factors as the increased intravascular pressure and blood flow seem to involve previously inactive vascular areas of the lungs in the circulation. The lung vascular bed of animals with the 1st type of responses is more plastic which can provide a better adaptation of the organism for extreme conditions.     

Motor and sensory fibres of neck muscle nerves in the cat

The numbers and sizes of nerve fibres to the dorsal neck muscles, splenius, complexus and biventer cervicis have been examined in the cat. The total number of fibres is unusually high as is the content of sensory fibres (estimated as the loss of fibres after ganglionectomy). The fibre spectra of these sensory nerves has an unusually large number of fibres in the group II and III range (3-7 mum) and differs markedly in this way from other muscle nerves. The motor fibres contain a high proportion (64-99%) in the gamma fibre size range. Large motor fibres are absent in the nerves to biventer cervicis (a slow muscle). The ratio of unmyelinated to myelinated fibres in neck muscle nerves is similar to that in hind legs at about 2.5:1.     

Changes in the enzymatic activities of beagle liver during maturation as assessed both in vitro and in vivo

1. We have examined changes in caffeine and trimethadione (TMO) metabolism in vivo, agents which are used as probe drugs. In this study the total body clearance (Cl) of caffeine and TMO was low 1 week after birth (week 1), increased rapidly from week 3, peaked and then decreased gradually until reaching the level for the mature, adult dog. The elimination half-life (t1/2) of caffeine and TMO was prolonged during week 1; however, it then gradually became shorter. Gradually it became longer and reached the level for the adult dog. The apparent volume of distribution (Vd) of caffeine did not change throughout the study. However, the Vd of TMO was only high during week 1. 2. The in vitro changes in a variety of typical substrates for seven different cytochrome P450 (CYP) isozymes were examined. In this study three different patterns of metabolism can be identified: (1) activity is low immediately after birth, increases, peaks and then decreases to the adult dog level (p-nitroanisole; CYP1A1, caffeine; CYP1A2, benzphetamine; CYP3A/2B(?), aniline; 2E1 and TMO; CYP2C9/2E1/3A4); (2) activity generally increases rapidly soon after birth, continues to increase, peaks and then gradually decreases to the adult level (phenytoin; CYP2C9); and (3) activity is high (about the same level as the adult) immediately after birth, decreases and then gradually increases to the adult level (erythromycin; CYP3A4/5). 3. The results of these in vivo and in vitro studies suggest that changes in enzyme activity are due to differences in P450 isoenzymes during development.     

Cortical blood flow response to hypercapnia during anaesthesia in Moyamoya disease

Cortical blood flow (CoBF) was measured continuously by the laser-Doppler method to evaluate the effect of hypercapnia on cortical blood flow during ten surgical procedures in ten young patients (mean +/- SD 9.3 +/- 6.4 yr) with Moyamoya disease. The CoBF was 42.8 +/- 13.4 (ml.100 g-1.min-1) during normocapnia (PaCO2 = 39.0 +/- 2.4 mmHg), and 38.7 +/- 14.4 during hypercapnia (PaCO2 = 47.1 +/- 2.5 mmHg). There was a decrease in CoBF with hypercapnia (P < 0.05) so that the normal CoBF response to hypercapnia was impaired during surgery in the patients with Moyamoya disease. He concluded that patients with Moyamoya disease have a precarious cerebral circulation and hypercapnia may be detrimental to the cortical circulation. This suggests that normocapnia is preferable to hypercapnia in patients with Moyamoya disease during anaesthesia.     

Horseradish peroxidase localization of masticatory muscle motoneurons in cat

Horseradish peroxidase has been injected into individual masticatory muscles in young and adult cats in order to determine the topography of the corresponding groups of motoneurons in the motor nucleus of the Vth nerve. The results obtained show a clear dorsoventral somatotopic distribution; the superior muscles have their motoneurons located dorsally in the nucleus and the inferior muscles ventrally; the two main jaw closers, temporalis and masseter, are represented in the dorsal and central parts of the nucleus; located more ventrally are the motoneurons for the pterygoideus medialis and lateralis, the jaw closers and abductor muscles; finally motoneurons for the jaw openers, and the anterior belly of the digastricus and mylohyoideus, occupy the ventromedial part of the nucleus. All muscles have been found to be represented along the entire length of the nucleus, with the same dorsoventral layering.     

Changes of lipoxygenase and fatty acid hydroperoxide lyase activities in bell pepper fruits during maturation

Developmental changes in fatty acid hydroperoxide lyase (HPO lyase) and lipoxygenase (LOX) during the maturation of bell pepper fruits (Capsicum annuum L. cv. Kyonami) were examined by means of activity measurements, immunological detection of both the enzymes, and analysis of the volatile compounds formed upon homogenization of the fruits. Both the enzyme activities decreased with maturation, and immunological studies showed that the amounts of the enzymes concomitantly decreased. The amounts of six-carbon aldehydes and alcohols formed from bell pepper fruits upon homogenization also decreased during maturation, and with the fully ripened red fruits, these volatile compounds were hardly detectable. These results suggest that the major factor contributing to the changes in the composition of volatile compounds during the maturation of bell pepper fruits was changes in the amounts of HPO lyase and LOX.     

The myocardial energetic active state. I. Oxygen consumption during tetanus of cat papillary muscle

The potential role of active state maintenance as a determinant of myocardial oxygen consumption (MVO2) has not been defined. Right ventricular papillary muscles from 15 cats were studied in a polarographic myograph at 23 degrees C in a Krebs-Ringer solution containing 7.5 mM Ca2+ and 10 mM caffeine. MVO2 was determined for isometric tetani at Lmax of 1-5 seconds' duration. Increases in tetanus duration related linearly to increments in both active tension time (delta active tension) and MVO2. In order to examine the oxygen cost of active state maintenance not attributable to associated tension generation, both the same isometric and 2.5- to 10.0-second lightly preloaded isotonic tetani were produced in nine muscles. For each tetanus duration the contribution throughout the contraction of developed force (preload) to MVO2 could be subtracted from overall isotonic MV02. In the absence of the MVO2 associated with force development, the active state duration was related linearly to MVO2, with a mean active state MVO2 of 2.42 +/- 0.29 nl O2/mg dry muscle/sec of isotonic tetanus; this MVO2 is 68% of the value of 3.58 +/- 0.42 nl O2/mg dry muscle/sec that was obtained for isometric tetanus at Lmax. This study identifies active state maintenance as the major determinant of MVO2 during myocardial tetanus and, furthermore, suggests the possibility that alterations in ative state intensity and duration may be the biochemical mechanism by which other determinants of MVO2 act in a more physiological setting.     

Relationship between velopharyngeal dimensions and palatal EMG during progressive hypercapnia

To examine the contribution of specific palatal muscles to velopharyngeal dimensions, we recorded electromyographic (EMG) activity in the levator veli palatini, the tensor veli palatini, and the palatoglossus while examining the velopharynx (VP) with videoendoscopy in eight awake normal adults. Simultaneous display of VP images and airflow provided precise timing of events. Video images and EMG signals were recorded during progressive hypercapnia. Every tenth breath was analyzed. For each selected breath, VP area, anteroposterior and lateral diameters, and EMG activity were determined at five points: beginning, middle, and end of inspiration and middle and end of expiration. VP measurements changed significantly during the respiratory cycle. Although maximum area was measured at end inspiration or middle expiration and minimum area at the beginning or end of the breath, respiratory-related changes in VP measurements and EMG activity were characterized by substantial inter- and intrasubject variability. This variability is similar to velopharyngeal behavior during nonrespiratory tasks and suggests that upper airway patency is determined by multiple factors.