CALCIUM UPTAKE INTO RAT PHEOCHROMOCYTOMA CELLS1

Abstract– 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.