Extracellular ATP (exATP) has been known to be a critical ligand regulating skeletal muscle differentiation and contractibility. ExATP synthesis was greatly increased with the high level of adenylate kinase 1 (AK1) and ATP synthase beta during C2C12 myogenesis. The exATP synthesis was abolished by the knock-down of AK1 but not by that of ATP synthase beta in C2C12 myotubes, suggesting that AK1 is required for exATP synthesis in myotubes. However, membrane-bound AK1beta was not involved in exATP synthesis because its expression level was decreased during myogenesis in spite of its localization in the lipid rafts that contain various kinds of receptors and mediate cell signal transduction, cell migration, and differentiation. Interestingly, cytoplasmic AK1 was secreted from C2C12 myotubes but not from C2C12 myoblasts. Taken together all these data, we can conclude that AK1 secretion is required for the exATP generation in myotubes.
Adenosine Triphosphate/*biosynthesis ; Adenylate Kinase/*metabolism ; Animals ; Cell Line ; Extracellular Space/metabolism ; Isoenzymes/*metabolism ; Mice ; Muscles/cytology/*metabolism

OBJECTIVETo study apoptosis and expression of apoptosis-related proteins in experimental different denervated guinea-pig facial muscle.

METHODAn experimental model was established with guinea pigs by compressing the facial nerve 30 second (reinnervated group) and resecting the facial nerve (denervated group). TUNEL method and immunohistochemical technique (SABC) were applied to detect the apoptosis and expression of apoptosis-related proteins bcl-2 and bax from 1st to 8th week after operation.

RESULTExperimentally denervated facial muscle revealed consistently increase of DNA fragmentation, average from(34.4 +/- 4.6)% to (38.2 +/- 10.6)%, from 1st week to 8th week after operation; Reinnervated facial muscle showed a temporal increase of DNA fragmentation, and then the muscle fiber nuclei revealed decreased DNA fragmentation along with the function of facial nerve recovered, latterly normal, average from (32.0 +/- 8.03)% to (5.6 +/- 3.5)%, from 1st week to 8th week after operation. In denervated group, bcl-2 and bax were expressed strongly; in reinnervated group, bcl-2 expressed consistently, but bax disappeared latterly along with the function of facial nerve recovered.

CONCLUSIONExpression of DNA fragmentation and apoptosis-related proteins in denervated muscle are general reaction to denervation. bcl-2 can prevent early apoptotic muscle fiber to survival until reinnervation. It is concluded that proteins control apoptosis may give information for possible therapeutic interventions to reduce the rate of muscle fiber death in denervated atrophy in absence of effective primary treatment.

Animals ; Apoptosis ; Denervation ; Facial Muscles ; cytology ; innervation ; metabolism ; Female ; Guinea Pigs ; Male ; Proto-Oncogene Proteins c-bcl-2 ; metabolism

We investigated the effects of simulated ischemia on intracellular Cl- concentration ([Cl-]i) in guinea pig ventricular myocardial cells and possible role of the [Cl-]i on the ischemia/reperfusion-induced arrhythmias in perfused rat hearts. Our results provided direct evidence that the [Cl-]i in ventricular muscle was increased under ischemic conditions, which suggested that activation of the Cl-(-)HCO3- exchanger by ischemia would partially contribute to the elevation of [Cl-]i. Application of stilbene derivatives or lowering Cl- concentration in perfusion solution delayed the onset of ischemia-induced deterioration in action potentials, pHi, [Cl-]i, and suppressed the incidence of ischemia/reperfusion-induced arrhythmias. The conclusion was made to emphasize the important role of intracellular Cl- homeostasis in cardiac physiology and pathogenesis of myocardial ischemia/reperfusion injury.
Action Potentials ; Animals ; Arrhythmias, Cardiac ; etiology ; metabolism ; Chlorides ; metabolism ; Guinea Pigs ; Hydrogen-Ion Concentration ; Microelectrodes ; Myocardial Reperfusion Injury ; complications ; metabolism ; Myocytes, Cardiac ; metabolism ; Papillary Muscles ; cytology

It is proved that polydatin has cardioprotection against ischemia-induced arrhythmia, but the electrophysiological mechanism is not clear. The aim of the present study was to investigate the effect of polydatin on action potential (AP) in ventricular papillary muscle and the underlying ionic mechanism in rat using intracellular recording and whole-cell patch clamp techniques. The results showed: (1) In normal papillary muscles, polydatin (50 and 100 µmol/L) shortened duration of 50% repolarization (APD(50)) and duration of 90% repolarization (APD(90)) in a concentration-dependent manner (P<0.01). But polydatin had no effects on resting potential (RP), overshoot (OS), amplitude of action potential (APA) and maximal rate of depolarization in phase 0 (V(max)) in normal papillary muscles (P>0.05). (2) In partially depolarized papillary muscles, polydatin (50 µmol/L) not only shortened APD(50) and APD(90) (P<0.05), but also decreased OS, APA and V(max) (P<0.05). (3) After pretreatment with glibenclamide (10 µmol/L), an ATP-sensitive K(+) channel blocker, the electrophysiological effect of polydatin (50 µmol/L) was partially inhibited. (4) Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 1 mmol/L), a nitric oxide (NO) synthase inhibitor, failed to abolish the effect of polydatin (50 µmol/L) on AP. (5) Polydatin (25, 50, 75 and 100 µmol/L) decreased L-type Ca(2+) current in ventricular myocytes in a concentration-dependent manner (P<0.05). (6) Polydatin (50 µmol/L) increased ATP-sensitive K(+) current in ventricular myocytes (P<0.05). The results suggest that polydatin can shorten the repolarization of AP in normal papillary muscle and inhibit AP in partially depolarized papillary muscle, which might be related to the blocking of L-type Ca(2+) channel and the opening of ATP-sensitive K(+) channel.
Action Potentials ; drug effects ; Animals ; Calcium Channels, L-Type ; metabolism ; Drugs, Chinese Herbal ; pharmacology ; Glucosides ; pharmacology ; Heart Ventricles ; cytology ; KATP Channels ; metabolism ; Male ; Papillary Muscles ; metabolism ; physiology ; Rats ; Rats, Sprague-Dawley ; Stilbenes ; pharmacology

To study the inotropic effect of enhanced Na(+)-Ca(2+) exchange in the rat papillary muscles and isolated heart, the developed tension in the rat papillary muscles was measured and the left ventricular functions were assessed in the isolated rat heart. E-4031, a selective activator for Na(+)-Ca(2+) exchange in rats, concentration-dependently increased the developed contractile tension in the rat papillary muscles (P<0.05, n=6) and the left ventricular functions in the isolated heart; KB-R7943, a selective Na(+)-Ca(2+) exchange inhibitor, exhibited opposite effect. A combination of 0.5 micromol/L ouabain and 3.0 micromol/L E-4031 resulted in a potentiation of the developed contractile tension of the rat papillary muscles from 0.25+/-0.03 g to 0.29+/-0.04 g. The combination also enhanced the augmentation of the left ventricular functions induced by ouabain. These results indicate that E-4031 exerts a positive inotropic effect on the rat papillary muscles and isolated heart via increasing the activity of Na(+)-Ca(2+) exchange, and potentiates the positive inotropic effects of ouabain.
Animals ; Cardiotonic Agents ; pharmacology ; Female ; Heart Ventricles ; cytology ; In Vitro Techniques ; Male ; Membrane Potentials ; drug effects ; Myocardial Contraction ; physiology ; Myocytes, Cardiac ; metabolism ; Ouabain ; pharmacology ; Papillary Muscles ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Wistar ; Sodium Channels ; metabolism ; Sodium-Calcium Exchanger ; physiology

OBJECTIVETo study the possibility of metallothionein (MT) participating in the process of ischemia/reperfusion protection.

METHODSThe model of pig latissimus dorsi island flap and cultured myocytes were used in this study. The island flap was preconditioned with ischemia and the cultured myocytes were treated with anoxia. MT was detected in the flap and the cultured myocytes instantly and at 12 and 24 hours after the treatment. The protection effect of precondition on flap ischemia/reperfusion damage was observed by recording flap necrosis and the serum LDH level. The protection effect of precondition on myocyte anoxia/reoxygenation damage was observed by recording the cell survival rate and MDA content. The change in the protection effect was also observed after the MT was inhibited by PD098059.

RESULTSThe content of MT in cultured myocytes increased obviously 12 hours after precondition. Similar result was observed in flap tissue 24 hours later. Compared with the non-conditioned flap, the necrosis areas of the preconditioned flaps were smaller, the serum LDH was lower. The survival rate of preconditioned cultured myocytes was higher compared with non-conditioned cells (P < 0.05). The content of MDA and the quantity of discharged LDH were less (P < 0.05). When MT was inhibited by PD098059, the delaying protection of precondition disappeared. The observed quotas at that time were the same with those of simple I/R or A/R groups (P > 0.05).

CONCLUSION24 hours after precondition, the flap and the cultured myocytes are protected from re-damage of I/R or A/R. MT is involved in this process.

Animals ; Cell Hypoxia ; physiology ; Cell Survival ; physiology ; Cells, Cultured ; Enzyme Inhibitors ; pharmacology ; Flavonoids ; pharmacology ; Ischemic Preconditioning ; L-Lactate Dehydrogenase ; blood ; metabolism ; Malondialdehyde ; metabolism ; Metallothionein ; drug effects ; metabolism ; Muscles ; cytology ; metabolism ; surgery ; Necrosis ; Reperfusion Injury ; metabolism ; Surgical Flaps ; pathology ; Swine ; Time Factors