Role of anions in the regulation of cell volume and intracellular pH in perfused rat mandibular salivary gland

Abstract

 To investigate the role of Cl^– in the regulation of the basolateral transporters of salivary acinar cells, we have measured cell volume and intracellular pH (pH_i) in perfused rat mandibular glands using proton 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-min period. Replacement with bromide, which substitutes for Cl^– on the Na⁺-K⁺-2Cl^– cotransporter, caused only a small (4%) reduction in cell volume. Replacement of Cl^– by glucuronate, isethionate or methylsulphate evoked a biphasic increase in pH_i consisting of a rapid initial increase followed by a slower secondary rise whose time course was similar to that of cell shrinkage. As judged by the effects of HCO₃ ^– omission, 100 μM 4,4’-diisothiocyanatostilbene-2,2’-disulphonic acid (DIDS) 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 in activating the exchanger. Therefore, while the upregulation of the exchanger following Cl^– replacement may be due in part to cell shrinkage, there is also evidence for the involvement of an anion-sensitive regulatory mechanism. This would be consistent with the hypothesis that both changes in cell volume and in intracellular Cl^– concentration contribute to the up-regulation of the exchanger following muscarinic stimulation.