Possible role of surface potential in the gating mechanism of Ca channels in cat adrenal chromaffin cells: studies with fura-2 microfluorometry

The cytosolic free Ca²⁺ concentration ([Ca]_in) in isolated cat chromaffin cells was measured by fura-2 microfluorometry. During 30 mM KCl depolarization or sucrose substitution for NaCl, a reduction in external Ca²⁺ concentration under optimal conditions paradoxically caused a rise in [Ca]_in and, in separate experiments, in catecholamine secretion. The results support a previously suggested role of surface potentials in the gating mechanism of Ca²⁺ channels.