M. Palmero et al., THE LOW-AFFINITY DIHYDROPYRIDINE RECEPTOR AND NA+ CA2+ EXCHANGER ARE ASSOCIATED IN ADRENAL-MEDULLARY MITOCHONDRIA/, Biochemical pharmacology, 50(6), 1995, pp. 879-883
The effect of Ca2+ channel-acting drugs on bovine adrenal mitochondria
Ca2+ movements was investigated. Mitochondrial Ca2+ uptake is perform
ed by an energy-driven Ca2+ uniporter with a Km of 20.9 +/- 3.2 mu M a
nd V-max of 148.1 +/- 7.2 nmol Ca-45(2+) min(-1) mg(-1). Ca2+ release
is performed through an Na+/Ca2+ antiporter with a Km for Na+ of 4.2 /- 0.5 mM, a V-max of 7.5 +/- 0.4 nmol Ca-45(2+) min(-1) mg(-1), and a
Hill coefficient of 1.4 +/- 0.2. Ca2+ efflux through the mitochondria
l Na+/Ca2+ exchanger was inhibited by several dihydropyridines (nitren
dipine, felodipine, nimodipine, (+)isradipine) and by the benzothiazep
ine diltiazem with similar potencies, In contrast, neither CGP 28392,
Bay-K-8644, amlodipine, nor verapamil had any effect on Ca2+ efflux. N
itrendipine at 20 mu M modified neither the Km nor the Hill coefficien
t for Na+, whereas the V-max was reduced to 2.9 nmol Ca-45(2+) min(-1)
mg(-1), thus demonstrating noncompetitive modulation of the Na+/Ca2exchanger. None of the Ca2+ channel-acting drugs assayed at 100 mu M a
ffected Ca2+ influx through the uniporter. Ca2+ channel blockers inhib
ited the Na+/Ca2+ antiporter and displaced the specific binding of [H-
3]nitrendipine to intact mitochondria with Ki values similar to the IC
(50)s obtained for the inhibition of the Ca2+ efflux. Ca2+ channel-act
ing drugs that did not inhibit the Na+/Ca2+ exchanger (amlodipine, CGP
28392, Bay-K-9644, and verapamil, at concentrations of 100 mu M or hi
gher) had no effect on [H-3]nitrendipine binding. These results sugges
t that the adrenomedullary mitochondrial dihydropyridine receptor is a
ssociated with the Na+/Ca2+ exchanger.