Differing potencies and dose-response characteristics in the ability of slow-calcium-channel blockers to reduce enzyme leakage in the calcium paradox.
In studies of the calcium paradox, we have used an isolated rat heart preparation to investigate the relationship between myocardial creatine kinase leakage and the concentration of slow-calcium-channel blockers (nifedipine or verapamil) in the perfusion fluid during a cycle of calcium reduction and repletion. The results indicated that enzyme leakage could be further reduced to a degree greater than that seen under conditions of a full calcium paradox (complete calcium depletion). Detailed dose-response studies with verapamil and nifedipine at a calcium concentration of 1.0 mM during a 20-min period of calcium repletion following a 10-min period of calcium reduction (12 microM calcium) revealed complex dose-response characteristics for each drug. In the dose range studied (0-20 microM), nifedipine was able to reduce enzyme leakage maximally by 57 +/- 8% and verapamil by 37 +/- 4%. Optimal concentrations for verapamil and nifedipine were 4.0 and 2.0 microM, respectively. Both drugs exhibited bell-shaped dose-response curves without a loss of efficacy at higher concentrations. There was no resumption in contractile activity in the drug-treated groups. Simultaneous use of verapamil and nifedipine at their optimal concentrations failed to improve the reduction in enzyme leakage to a reduction greater than that observed with one drug alone.
Baker
J E
JE
Hearse
D J
DJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003326:Coronary Circulation / Q000187:drug effects*; D003402:Creatine Kinase / Q000097:blood*; D004305:Dose-Response Relationship, Drug; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009543:Nifedipine / Q000494:pharmacology*; D051381:Rats; D014700:Verapamil / Q000494:pharmacology*
D007473:Ion Channels; D014700:Verapamil; D003402:Creatine Kinase; D009543:Nifedipine; D002118:Calcium