Calcium Uptake Into Rat Pheochromocytoma Cells1

The uptake of 45Ca2+ into cell suspensions prepared from a transplantable rat pheochromocytoma was measured. The uptake of Ca2+ into these cells is biphasic; there is a rapid, initial uptake of Ca+, followed by a slower uptake that proceeds at a linear rate for at least 10min at 37°C. The uptake of Ca2+ is a linear function of the external Ca2+ concentration over the range of 0.13‐2.5 mm‐Ca2+ Incubation of the cells in a medium containing 56mm‐K+ results in a 2‐3 fold increase in the uptake of Ca2+ into the cells; 56mm‐K+ increases both phases of Ca2+ uptake. The cells apparently lack a mechanism to inactivate this 56 mm‐K+‐induced increase‐in Ca2+ permeability. Two inhibitors of K+ stimulated catecholamine secretion, diphenylhydantoin and verapamil, both inhibit K +‐stimulated Ca2+ uptake. These results provide a direct demonstration of the stimulus‐coupled uptake of Ca2+ into chromaffin cells, and provide additional evidence for the correlation of Ca2+ uptake with catecholamine secretion by these cells.