In vitro interaction between bovine adrenal medullary cell membranes and chromaffin granules: specific control by Ca2+.

The control of the in vitro interaction between bovine adrenal medullary plasma membranes and chromaffin granules by calcium has been studied. This interaction, which has previously been shown to result in the release of the soluble granular content, is a possible cell-free model for exocytosis. The plasma membrane-induced catecholamine release was stimulated when the [Ca2+] exceeded 2x10(-7) M. A maximal release was reached at 10(-5) M with a half maximal response around 10(-6)M. Mg2+ was not able to stimulate the system in the absence of Ca2+. These data suggest a high specificity of the calcium controlled exocytotic mechanism and the absence of an antagonism by high concentrations (10(-5)-10(-1) M) of magnesium at the exocytotic site itself.