ROLE OF ANIONS IN THE REGULATION OF CELL-VOLUME AND INTRACELLULAR PH IN PERFUSED RAT MANDIBULAR SALIVARY-GLAND

To investigate the role of Cl- in the regulation of the basolateral tr ansporters of salivary acinar cells, we have measured cell volume and intracellular pH (pH(i)) in perfused rat mandibular glands using proto n NMR spectroscopy and BCECF fluorometry respectively. When perfusate Cl- was replaced by glucuronate, isethionate, methylsulphate, nitrate or thiocyanate, cell volume decreased slowly by about 15% over a 10-mi n period. Replacement with bromide, which substitutes for Cl- on the N a+-K+-2Cl(-) cotransporter, caused only a small (4%) reduction in cell volume. Replacement of Cl- by glucuronate, isethionate or methylsulph ate evoked a biphasic increase in pH(i) consisting of a rapid initial increase followed by a slower secondary rise whose time course was sim ilar to that of cell shrinkage. As judged by the effects of HCO3- omis sion, 100 mu M 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DI DS) and 1 mM amiloride, the initial rise in pH(i) was due to Cl-/HCO3- , exchange while the secondary rise resulted from activation of Na+/H exchange. Although replacement of Cl- by nitrate or thiocyanate also caused cell shrinkage, these substituting anions were less effective i n activating the exchanger. Therefore, while the upregulation of the e xchanger following Cl- replacement may be due in part to cell shrinkag e, there is also evidence for the involvement of an anion-sensitive re gulatory mechanism. This would be consistent with the hypothesis that both changes in cell volume and in intracellular Cl- concentration con tribute to the up-regulation of the exchanger following muscarinic sti mulation.