Selective inhibition of Na+-induced Ca2+ release from heart mitochondria by diltiazem and certain other Ca2+ antagonist drugs

• Published in: The Journal of biological chemistry 1982-06, Vol.257 (11), p.6000-6002
• Main Authors: Vághy, P L, Johnson, J D, Matlib, M A, Wang, T, Schwartz, A
• Format: Article
• Language: English
• Subjects: Animals; Benzazepines - pharmacology; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Diltiazem - pharmacology; Kinetics; Mitochondria, Heart - drug effects; Mitochondria, Heart - metabolism; Rabbits; Ruthenium Red - pharmacology; Sodium - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(20)65094-3

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.