Extracellular Mg 2+ regulates the intracellular Na + concentration in rat sublingual acini

Abstract

The intracellular free Na + concentration ([Na +] i) increases during muscarinic stimulation in salivary acinar cells. The present study examined in rat sublingual acini the role of extracellular Mg 2+ in the regulation of the stimulated [Na +] i increase using the fluorescent sodium indicator benzofuran isophthalate (SBFI). The muscarinic induced rise in [Na +] i was approximately 4-fold greater in the absence of extracellular Mg 2+. When Na + efflux was blocked by the Na +,K +-ATPase inhibitor ouabain, the stimulated [Na +] i increase was comparable to that seen in an Mg 2+-free medium. Moreover, ouabain did not add further to the stimulated [Na +] i increase in an Mg 2+-free medium suggesting that removal of extracellular Mg 2+ may inhibit the Na + pump. In agreement with this assumption, ouabain-sensitive Na + efflux and rubidium uptake were reduced by extracellular Mg 2+ depletion. Our results suggest that extracellular Mg 2+ may regulate [Na +] i in sublingual salivary acinar cells by modulating Na + pump activity.