Calcium transients in single adrenal chromaffin cells detected with aequorin

The effect of 55 mM K+ and nicotine on intracellular free calcium was monitored in bovine adrenal chromaffin cells microinjected with aequorin. In contrast to results with quin 2, which suggested that stimulation of chromaffin cells resulted in sustained rises in free calcium, aequorin measurements showed that 55 mM K+ and nicotine resulted in a transient (60-90 s) elevation of free calcium. The peak free calcium and duration of the transient elicited by nicotine were dose-dependent. The concentration of nicotine (10 microM) giving a maximal secretory response gave a peak rise in free calcium of up to 1 microM. 55 mM K+ which only releases 30% of the catecholamine released by 10 microM nicotine generated a calcium transient indistinguishable from that due to 10 microM nicotine. These results support the idea that nicotine agonists generate an alternative second messenger in addition to the rise in free calcium.