Selective inhibition of Na+-induced Ca2+ release from heart mitochondria by diltiazem and certain other Ca2+ antagonist drugs.
The effect of Ca2+ antagonist drugs on Ca2+ uptake and Na+-induced Ca2+ release by isolated rabbit heart mitochondria has been studied using arsenazo III and dansylaziridine-labeled troponin C as Ca2+ indicators. Mitochondria accumulated 20 nmol of Ca2+/mg of protein by a respiration-dependent process. A23187, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, or Na+ induced a release of Ca2+ from Ca2+-loaded and ruthenium red (RR)-treated mitochondria. Ca2+ antagonist drugs had no effect on the Ca2+ uptake process or on Ca2+ release induced either by A23187 or by carbonyl cyanide p-trifluoromethoxyphenylhydrazone but they were effective in inhibiting the Na+-induced Ca2+ release process. The drug concentrations that resulted in 50% inhibition of Na+-induced Ca2+ release were 7, 12, 13, 66, and 150 microM for diltiazem, prenylamine, fendiline, nifedipine, and verapamil, respectively. In the absence of RR, the net amount of Ca2+ released by Na+ was less than that which occurred in the presence of RR due to the simultaneous operation of both the Ca2+ uptake and the Ca2+ release processes. Under these conditions, the inhibition of Ca2+ uptake by RR brought about a complete release of Ca2+ from the mitochondria, and the inhibition of the Na+-induced Ca2+ release by diltiazem resulted in an apparent uptake of Ca2+ by the mitochondria. These results indicate that diltiazem and certain other Ca2+ antagonist drugs may be selective inhibitors of the Na+/Ca2+ antiporter in heart mitochondria much like ruthenium red is a selective inhibitor of the Ca2+ uniporter.
D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology*; D007700:Kinetics; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*
D001552:Benzazepines; D002121:Calcium Channel Blockers; D012430:Ruthenium Red; D012964:Sodium; D004110:Diltiazem; D002118:Calcium