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 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 mu M 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.