The low-affinity dihydropyridine receptor and Na+/Ca2+ exchanger are associated in adrenal medullary mitochondria.
The effect of Ca2+ channel-acting drugs on bovine adrenal mitochondria Ca2+ movements was investigated. Mitochondrial Ca2+ uptake is performed by an energy-driven Ca2+ uniporter with a Km of 20.9 +/- 3.2 microM and Vmax of 148.1 +/- 7.2 nmol 45Ca2+ 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 Vmax of 7.5 +/- 0.4 nmol 45Ca2+ min-1 mg-1, and a Hill coefficient of 1.4 +/- 0.2 Ca2+ efflux through the mitochondrial Na+/Ca2+ exchanger was inhibited by several dihydropyridines (nitrendipine, felodipine, nimodipine, (+)isradipine) and by the benzothiazepine diltiazem with similar potencies. In contrast, neither CGP 28392, Bay-K-8644, amlodipine, nor verapamil had any effect on Ca2+ efflux. Nitrendipine at 20 microM modified neither the Km nor the Hill coefficient for Na+, whereas the Vmax was reduced to 2.9 nmol 45Ca2+ min-1 mg-1, thus demonstrating noncompetitive modulation of the Na+/Ca2+ exchanger. None of the Ca2+ channel-acting drugs assayed at 100 microM affected Ca2+ influx through the uniporter. Ca2+ channel blockers inhibited the Na+/Ca2+ antiporter and displaced the specific binding of [3H]nitrendipine to intact mitochondria with Ki values similar to the IC50s obtained for the inhibition of the Ca2+ efflux. Ca2+ channel-acting drugs that did not inhibit the Na+/Ca2+ exchanger (amlodipine, CGP 28392, Bay-K-9644, and verapamil, at concentrations of 100 microM or higher) had no effect on [3H]nitrendipine binding. These results suggest that the adrenomedullary mitochondrial dihydropyridine receptor is associated with the Na+/Ca2+ exchanger.
Palmero
M
M
Departamento de Neuroquímica, Universidad de Alicante, Spain.
Gutierrez
L M
LM
Hidalgo
M J
MJ
Reig
J A
JA
Ballesta
J J
JJ
Viniegra
S
S
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D008928:Mitochondria / Q000378:metabolism; D009568:Nitrendipine / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D009568:Nitrendipine; D012964:Sodium; D002118:Calcium