Deprivation of Na +, Ca 2+ and Mg 2+ from the extracellular solution increases cytosolic Ca 2+ and stimulates catecholamine secretion from cultured bovine adrenal chromaffin cells

Abstract

We report here that exposing cultured chromaffin cells to a low ionic strength medium (with sucrose in place of NaCl to maintain osmolarity) can induce a marked elevation in cytosolic Ca 2+ concentration ([Ca 2+](i)) and catecholamine (CA) release. To determine the underlying mechanism, we first studied the effects of low [Na +](o) on single cell [Ca 2+](i) (using fluo-3 as Ca 2+ indicator) and CA release from many cells. In a Mg 2+ and Ca 2+-deficient medium, lowering the external concentration of Na 2+ ([Na +](o)) evoked CA secretion preceded by a transitory [Ca 2+](i) rise, the amplitude of which was inversely related to [Na +](o). By contrast, in the presence of either [Ca 2+](o) (2 mM) and [Mg 2+](o) (1.4 mM) or [Mg 2+](o) alone (3.4 mM), lowering the ionic strength was without effect. Furthermore, in a physiologic [Na +](o), [Ca 2+](o) and [Mg 2+](o) medium, two or three consecutive applications of the cholinergic agonist oxotremorine-M (oxo-M) consistently evoked a substantial [