Calcium channels in rat brain synaptosomes: identification and pharmacological characterization. High affinity blockade by organic Ca2+ channel blockers

摘要: Rat brain synaptosomes are shown to contain functional voltage-sensitive Ca2+ channels that inhibited by organic channel blockers. Depolarization of with high K+ stimulates uptake 45Ca2+ which is biphasic in its time course. Replacement external Na+ choline eliminates the slower phase depolarization-stimulated uptake, leaving only a rapid process terminates within 1 sec. This rapid, tetrodotoxin-insensitive can be inactivated prior depolarization synaptosomes. has no effect on rate synatptosomal 22Na+ efflux. These results interpreted as ruling out Na+/Ca2+ exchange mediator uptake. A portion (30 50%) nitrendipine, [3H]norepinephrine release from In Na+, inhibition constant (Kapp) for nitrendipine 56 nM. The potency increased absence (Kapp = 1.7 nM), such correlates more closely equilibrium dissociation [3H] binding (Kd 0.35 nM). Other blockers (nifedipine, verapamil, D600, and dilitiazem) inhibit potencies all tested us reasonable agreement their potencies, observed other laboratories, smooth cardiac muscle. data demonstrate existence active synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)