Excitatory effect of Cd2+ on cat adrenal chromaffin cells

To understand the mechanism(s) underlying the Cd2+- and Co2+-induced increa ses in the cytosolic free Ca2+ concentration ([Ca](i)) in cat adrenal chrom affin cells, we used nystatin-perforated patch recording method and fura-2 microfluorometry. Under the current-clamp conditions, the external applicat ion of 5 x 10(-7) M Cd2+ slowly depolarized the cells resulting in the burs ting of action potentials. Under the voltage-clamp conditions, Cd2+ evoked a slow inward current accompanied by a decrease of K+ conductance at a hold ing potential of -40 mV, and Co2+ mimicked Cd2+ action. In some cells (16%) , Cd2+ evoked an additional rapid transient outward current associated with an increased K+ conductance and a successive slow inward current. The Cd2-induced inward current was activated in a concentration-dependent manner w ith a half-maximum concentration of 9.3 X 10(-8) M. The Cd2+- and Co2+-indu ced [Ca](i) increases measured with fura-2 microfluorometry were maximal at 10(-6) and 10(-5) M, respectively, and the higher concentrations of both c ations caused the smaller responses. Additional transient increase in [Ca]( i) was often evoked upon the removal of relatively higher concentrations of these metals. It was concluded that the Cd2+-induced membrane depolarizati on due to the decrease in K+ conductances evoked the bursting firings resul ting in the increase in [Ca](i), and consequently might stimulate the catec holamine secretion. (C) 1999 Elsevier Science B.V. All rights reserved.