Inactivation of the early calcium uptake and noradrenaline release evoked by potassium in cultured chromaffin cells.

Upon stimulation with a 59 mM K solution (59K), 45Ca uptake into cultured bovine adrenal chromaffin cells quickly enhanced to reach a plateau within 60 sec. 45Ca transients could be clearly measured with a time resolution (10 sec) and a net Ca uptake (75 times the basal uptake) that considerably improve data reported in other recent papers; this experimental design allows the direct comparison of 45Ca transient data with electrophysiological measurements of chromaffin cell Ca currents. In addition, it is shown that upon sustained depolarization with 59K both, the rates of 45Ca uptake and 3H-noradrenaline release decline in a parallel manner, suggesting that the voltage-dependent Ca channel activity modulates the kinetics of the early secretory response.