Mitochondrial Ca2 antagonist binding sites are associated with an inner mitochondrial membrane anion channel

Abstract:  Mitochondrial Ca2+ antagonist binding sites are associated with an inner mitochondrial membrane anion channel. Zernig G, Graziadei I, Moshammer T, Zech C, Reider N, Glossmann H. Institut f?r Biochemische Pharmakologie, Universit?t Innsbruck, Austria. The inner mitochondrial membrane contains specific Ca2+ antagonist binding sites unrelated to the L-type Ca2+ channel. The mitochondrial 1,4-dihydropyridine (DHP) and phenylalkylamine sites are reciprocally allosterically coupled, require anions (e.g., Cl-, No3-) for optimal binding, and are inhibited by purine and pyrimidine nucleotides in a noncompetitive manner. In mitochondrial swelling experiments, a concentration-depend ent inhibition of an inner mitochondrial membrane anion channel (IMAC) by Ca2+ antagonists from different chemical classes can be demonstrated. Under the conditions of the swelling experiments, affinity of different Ca2+ antagonists and amiodarone, a known IMAC inhibitor, for the mitochondrial (+/-)-[3H]nitrendipi ne binding site (Kd, 7.2 +/- 2.0 microM; Bmax, 1.03 +/- 0.37 nmol/mg of protein) strongly correlated with their inhibitory potency for the IMAC. Linear regression of pIC50 values for IMAC-induced swelling versus pIC50 values for (+/-)-[3H]nitrendipi ne binding inhibition yielded a correlation coefficient of 0.91 for all tested DHPs (n = 12, p less than 0.001). Amiodarone inhibited (+/-)-[3H]nitrendipi ne binding and IMAC-induced swelling with pIC50 values of 6.11 and 5.93, respectively. The correlation coefficient between binding and inhibition of IMAC-induced swelling for amiodarone and all tested Ca2+ antagonists (including non-DHP compounds) was 0.76 (n = 20, p less than 0.001), with the slopes approaching unity. These results suggest the association of the mitochondrial Ca2+ antagonist binding sites with an IMAC. PMID: 1698252 [PubMed - indexed for MEDLINE]