Inactivation of 45Ca2+ uptake by prior depolarization of PC12 cells.

45Ca2+ uptake evoked by depolarization of PC12 pheochromocytoma cells with K+ was reduced approximately 90% by prior depolarization in Ca2+-containing medium. Prior depolarization without added Ca2+ reduced 45Ca2+ uptake by only about 20%. The Ca2+ channel agonists, BAY K 8644 and CGP 28392, had no effect on inactivation of 45Ca2+ uptake. These findings suggest that (1) voltage-gated Ca2+ channels of PC12 cells undergo inactivation, (2) inactivation is Ca2+-dependent rather than voltage-dependent, and (3) Ca2+ channel agonists do do not promote Ca2+ flux by inhibiting Ca2+ channel inactivation.