Sodium- and Calcium-Dependent Somatostatin Release from Dissociated Cerebral Cortical Cells in Culture*

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Abstract
The influence of membrane depolarization on somatostatin release from cerebral cortical neurons was examined. Fetal rat telencephalic cells, obtained by mechanoenzymatic dispersal, were maintained as organotypic monolayer cultures for 12 days before experimental studies. The immunoreactive somatostatin (IRS) released into the medium during a treatment epoch was compared to the amount released from the same cells during an immediately preceding control period. Potassium (60 mM) induced an increase in IRS secretion which was dependent on extracellular calcium concentration and could be prevented by the addition of the calcium channel blockers, cobalt or verapamil. Depolarization by veratridine, a sodium ionophore, also stimulated IRS release. The effect of veratridine was reversed by simultaneous exposure of the cells to either tetrodotoxin, a sodium channel blocker, or verapamil, a calcium channel blocker. These findings indicate that IRS release by cerebral cortical cells is stimulated by membrane depolarization and is dependent on both Na+ and Ca++ entry into the cells.