Energy-dependent accumulation of calcium antagonists in catecholamine storage vesicles

The calcium antagonists verapamil, nitrendipine, mibefradil, and amlodipine accumulate in chromaffin granule ghosts with apparent equilibrium partitio n coefficients [(mol/mg membrane lipid)/(mol/mg solvent water)] of 246 +/- 105 (N = 8), 2700 +/- 600 (N = 4), 7400 +/- 2200 (N = 4), and 8100 +/- 1100 (N = 5), respectively. In the presence of 1.2 mM MgATP, the partition coef ficients were 854 +/- 206 (N = 10), 2300 +/- 600 (N = 4), 32,700 +/- 8,900 (N = 7), and 20,300 +/- 5,000 (N = 11) for verapamil, nitrendipine, mibefra dil, and amlodipine, respectively. Except for nitrendipine, the apparent pa rtition coefficients in the presence of MgATP were significantly different from the control (P < 0.001). For amlodipine and verapamil, the vacuolar H-ATPase inhibitors bafilomycin A(1) (30 nM) and N-ethylmaleimide (2 mM) and the protonophore (uncoupler) carbonyl cyanide m-chlorophenylhydrazone (CCC P, 10 mu M) completely blocked the increase in partition coefficients in re sponse to MgATP. The extra amlodipine, mibefradil, and verapamil that accum ulated in response to MgATP were released into the medium by CCCP (10 mu M) by 18% (N = 5), 30% (N = 5), and 88% (N = 5) for amlodipine, mibefradil, a nd verapamil, respectively. Thus, amlodipine, mibefradil, and verapamil, bu t not nitrendipine, accumulate in catecholamine storage vesicles in respons e to Delta mu(H+) generated by the endogenous V-type H+-ATPase, and are par tially released by de-energetisation. Hence, these calcium antagonists can reach unexpectedly high concentrations in certain target cells, and give ph armacodynamic properties not shared by nitrendipine. BIOCHEM PHARMACOL 59;2 :123-129, 2000. (C) 1999 Elsevier Science Inc.