ATP-Dependent Ca2+Accumulation by Microvesicles Isolated from Bovine Neurohypophyses

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Abstract
Microvesicles with and witout coats were isolated from bovine neurohypophyses by a series of ultracentrifugation steps. They were similar to microvesicles previously isolated from the brain. In the presence of ATP and Mg2+, the microvesicles accumulated Ca. Oxalate stimulated and the Ca2+ ionophore A23187 [calcimycin] inhibited Ca accumulation. In the presence of Ca2+ and Mg2+ the microvesicles also demonstrated ATPase activity. As judged by sodium dodecyl sulfate electrophoresis in polyacrylamide gels microvesicle protein composition was very different from that of neurosecretory granules; apparently they are not granule membranes retrieved after exocytosis. They may have an important function in the regulation of Ca2+ concentration.