CONTROL OF NA-CELLS BY CYTOSOLIC CL- AND NA+( TRANSPORT IN SALIVARY DUCT EPITHELIAL)

The duct cells of the mandibular glands of mice (and many other mammal ian salivary glands) absorb NaCl from an isotonic, Na+-rich primary sa liva, formed by the gland's secretory endpieces, utilising an amilorid e-sensitive Na+ channel in the apical (luminal) domain of the plasma m embranes. The present study focuses on the mechanisms whereby the apic al membrane Na+ conductance is controlled so that the rate of Na+ infl ux from lumen to cytosol via the Na+ channels is matched to the rate o f Na+ extrusion from cytosol to interstitium via the basolateral Na+-K +-ATPase (so called homocellular regulation or epithelial cross-talk). Our results show that the apical membrane Na+ conductance is not cont rolled by a sensor of extracellular (luminar) Na+, as has been previou sly believed, but by sensors of cytosolic Na+ and Cl- which down-regul ate the Na+ channels when the cytosolic concentration of either ion in creases. These effects of cytosolic Na+ and Cl- are mediated, respecti vely, by G proteins of the G(i) and G(o) subclasses.