L-TYPE CA2+ CHANNEL AND NA+ CA2+ EXCHANGE INHIBITORS REDUCE CA2+ ACCUMULATION IN REPERFUSED SKELETAL-MUSCLE/

It is known that extracellular Ca2+ accumulates within skeletal muscle after prolonged periods of ischemia and reperfusion. In this study, w e determined whether the L-type Ca2+ channel and the Na+/Ca2+ exchange r mediated Ca2+ influx and whether Ca2+ accumulation limited the metab olic and contractile recovery of reperfused skeletal muscle. Contracti ng rat hindlimbs (1-Hz twitch) exposed to 40 min of no-flow ischemia w ere reperfused with diltiazem (500 mu M) or 3,4-dichlorobenzamil (300 mu M) to block the Na+/Ca2+ exchanger and/or the L-type Ca2+ channel. High inhibitor concentrations were used to counter the binding of dilt iazem and 3,4-dichlorobenzamil to albumin and red blood cells. Muscle Ca2+ accumulation, contractile function, and energy metabolism were as sessed by measuring intracellular Ca2+ concentration ([Ca2+](i)), Ca2 influx, twitch tension, and high-energy phosphagens [ATP, total adeni ne nucleotides (TAN) and phosphocreatine (PCr)]. Compared with control reperfusion, diltiazem and 3,4-dichlorobenzamil reduced Ca2+ influx a nd attenuated the rise in [Ca2+](i) in the fast-oxidative glycolytic p lantaris (Pi) and the fast-glycolytic white gastrocnemius (WG). The in hibitor-induced decrease in Ca2+ influx was 1.5- to 2-fold greater wit h 3,4-dichlorobenzamil than with diltiazem. Coinciding with the reduce d Ca2+ accumulation, diltiazem and 3,4-dichlorobenzamil enhanced the r esynthesis of ATP (Pl and WG), PCr (Pl and WG), and TAN (Pl) compared with control reperfusion. 3,4-Dichlorobenzamil also augmented twitch-t ension recovery. We conclude that Ca2+ accumulation during reperfusion 1) arises from L-type Ca2+ channel and Na+/Ca2+ exchange activation; and 2) impairs the metabolic and contractile recovery of skeletal musc le.