Beta-adrenergic upregulation of the Na(+)-K(+)-2Cl- cotransporter in 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 (pHi) of rat parotid acini from an NH4(+)-induced alkaline load. This recovery was markedly inhibited by the loop diuretic bumetanide and by Cl- removal, indicating that it is largely due to NH4+ entry via the basolateral Na(+)-K(+)-2Cl- cotransporter. The rate of recovery of pHi was enhanced threefold by pretreatment (37.5 s) with isoproterenol (K1/2 = 21.5 nM) or norepinephrine (in the presence of phentolamine), and blocked by the beta 1-specific antagonist atenolol, indicating an upregulation of cotransport activity by beta 1-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 of protein kinase A. Physiologically, such an upregulation of the acinar Na(+)-K(+)-2Cl- cotransporter 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 beta-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.
Paulais
M
M
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
Turner
R J
RJ
D000818:Animals; D001692:Biological Transport; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010306:Parotid Gland / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D015854:Up-Regulation
D002712:Chlorides; D011943:Receptors, Adrenergic, beta; D002034:Bumetanide; D012964:Sodium; D000242:Cyclic AMP; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium