CALCIUM-DEPENDENCE OF LARGE DENSE-CORED VESICLE EXOCYTOSIS EVOKED BY CALCIUM INFLUX IN BOVINE ADRENAL CHROMAFFIN CELLS

We used the perforated-patch technique to examine the relationship bet ween Ca2+ entry and exocytosis of large dense-cored vesicles in bovine adrenal chromaffin cells. Exocytosis evoked by single-step depolariza tions was monitored by capacitance detection. Ca2+ entry was varied by changing external calcium concentration, stepping to different test p otentials, depolarizing for different durations, or applying blockers of specific calcium channel subtypes. Regardless of protocol, the amou nt of exocytosis was strictly related to the integral of the voltage-c lamped calcium current, raised to a power of similar to 1.5. Thus, des pite the complexities of transient and nonuniform changes in submembra ne calcium concentration produced by voltage-gated calcium entry, the calcium dependence of large dense-cored vesicle fusion under condition s of minimal stimulation is well approximated by a simple transfer fun ction of summed calcium entry.