REGULATION OF CHANGES IN CYTOSOLIC CA2-GLAND ACINI EXPOSED TO CARBACHOL AND ATP( AND NA+ CONCENTRATIONS IN RAT SUBMANDIBULAR)

The relationship between cytosolic concentrations of Ca2+ (Ca-i(2)) an d Na+ (Na-i(+)) were studied in preparations of rat submandibular and pancreatic acini loaded with the Ca2+-sensitive dye Fura-2 or the Na+- sensitive dye SBFI. Pancreatic acini showed no changes in Na: during e ither transient or persistent changes in Ca-i(2+). Increases in Ca-i(2 +) produced by exposure of submandibular gland acini to carbachol, a m uscarinic cholinergic agonist, were followed by an increase in Na-i(+) after a delay of 5-10 s. When Ca2+ stores were mobilized without Ca2 influx Na: also increased, but in acini loaded with BAPTA, a nonfluor escent Ca2+ chelator, the transient increase in Ca2+ caused by mobiliz ation of stored Ca2+ was virtually abolished, as was the increase in N a-i(+). In the presence of ionomycin, increases in Ca-i(2+) were follo wed by increases in Na-i(+). Ca2+-dependent increases in Na-i(+) were abolished in Na+-free buffer and by the presence of furosemide, a bloc ker of Na+-K+-2Cl(-) cotransport. In other studies, extracellular ATP (ATP,) produced an increase in Ca-i(2+) and Na-i(+). The steady-state increase in Ca-i(2+) was reduced by increasing extracellular Na+ conce ntrations (Na-0(+)) in dose-dependent fashion (IC50 = 16.4 +/- 4.7 mM Na+). Likewise, increasing Na-0(+) reduced ATP(0)-stimulated Ca-45(2+) uptake at steady state (IC50 = 15.8 +/- 9.2 mM Na+). Changing Na-0(+) had no effect on carbachol-stimulated increases in Ca-i(2+) We conclu de that, in rat submandibular gland acini, ATP(0) promotes an increase in Ca-i(2+) and Na-i(+) via a common influx pathway and that, under p hysiologic conditions, Na+ significantly limits the ATP(0)-stimulated increase in Ca-i(2+). In the presence of carbachol, however, Na-i(+) r ises in Ca-i(2+)-dependent fashion in submandibular gland acini via st imulation of Na+-K+-2Cl(-) cotransport. (C) 1996 Wiley-Liss, Inc.