Relaxation in ferret ventricular myocytes: role of the sarcolemmal Ca ATPase.
In ferret ventricular myocytes the rate of intracellular Ca concentration [Ca]i decline and relaxation is remarkably fast (compared with rabbit and rat) under conditions where both the sarcoplasmic reticulum Ca uptake and Na/Ca exchange are inhibited. Here we explore the possibility that this rapid [Ca]i decline in ferret cells is attributable to the sarcolemmal Ca ATPase by using carboxyeosin (a potent inhibitor of the sarcolemmal Ca-ATPase). We compare the effects of carboxyeosin with those of elevated extracellular [Ca] ([Ca]o) (a thermodynamic approach to limit Ca transport by the sarcolemmal Ca ATPase). In rabbit cells, carboxyeosin and high [Ca]o slowed [Ca]i decline similarly and both virtually abolished [Ca]i decline when mitochondrial Ca uptake was also inhibited. In ferret cells, carboxyeosin treatment produced these same effects on [Ca]i decline, but high [Ca]o did not mimic them. Moreover, only in carboxyeosin-treated ferret cells did additional inhibition of mitochondrial Ca uptake nearly abolish [Ca]i decline. We conclude that, carboxyeosin loading can inhibit the sarcolemmal Ca-ATPase in intact myocytes; that this pump seems likely to be responsible for the much faster relaxation observed in ferret cells after block of SR Ca accumulation and Na/Ca exchange transport and that the sarcolemmal Ca pump apparently has different characteristics in rabbit and ferret ventricular myocytes.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D005289:Ferrets / Q000502:physiology*; D005456:Fluorescent Dyes; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology; D066298:In Vitro Techniques; D007211:Indoles; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology* / Q000201:enzymology / Q000648:ultrastructure; D011817:Rabbits; D012508:Sarcolemma / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D016276:Ventricular Function
D005456:Fluorescent Dyes; D007211:Indoles; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000252:Calcium-Transporting ATPases; C048960:indo-1; D002118:Calcium