Rat Parotid Acinar Cells

We used the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6')-carboxyfluorescein to monitor the recovery of the intracellular pH (pH,) of rat parotid acini from an NH+-induced alkaline load. This recovery was markedly inhibited by the loop diuretic bumetanide and by Clremoval, indicating that it is largely due to NH' entry via the basolateral Na'-K+2Clcotransporter. The rate of recovery of pHi was enhanced threefold by pretreatment (37.5 s) with isoproterenol (K112 = 21.5 nM) or norepinephrine (in the presence of phentolamine), and blocked by the #,-specific antagonist atenolol, indicating an upregulation of cotransport activity by ,81-adrenergic stimulation. The effect of isoproterenol was prevented by protein kinase inhibitors and mimicked by cAMP analogues, and by maneuvers known to increase cytosolic cAMP levels in these cells, consistent with the involvement ofprotein kinase A. Physiologically, such an upregulation of the acinar Na'-K+-2CIcotransporter would lead to an increase in acinar chloride uptake across the basolateral membrane, and consequently, an increase in overall chloride and fluid secretion. Prevention of this upregulation by t-blockers and possibly by other commonly used clinical agents may account for the dry mouth and dry eyes experienced by some patients taking these medications. (J. Clin. Invest. 1992. 89:1142-1147.)