A role of Sodium Bicarbonate Cotransporter(NBC) in HCO3 - Formation in Human Salivary Gland Acinar Cells
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The sodium bicarbonate cotransporter (NBC) protein is functionally expressed in salivary glands. In this experiment, we examined the role of NBC in HCO₃ -formation in human parotid gland acinar cells. Intracellular pH (pHi) was measured in 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) -loaded cells. Acetazolamide (0.1 mM) and 4,4'-diisothio cyanatostilbene-2,2'-disulphonic acid (DIDS, 0.5 mM) were used as specific inhibitors of carbonic anhydrase and NBC, respectively. The degree of inhibition was assessed by measuring the pHi recovery rate (△pHi/min) after cell acidification using an ammonium prepulse technique. In control experiments, △pHi/min was 1.40 ± 0.06. Treatment of cells with 0.5 mM DIDS or 0.1 mM acetazolamide significantly reduced △pH/min to 1.14 ± 0.14 and 0.74 ± 0.15, respectively. Simultaneous application of DIDS and acetazolamide further reduced △ pHi/min to 0.47 ± 0.10. Therefore, DIDS and acetazolamide reduced △pHi/min by 19 % and 47 %, respectively, while simultaneous application of both DIDS and acetazolamide caused a reduction in △pHi/min of 67 %. These results suggest that in addition to carbonic anhydrase, NBC also partially contributes to HCO₃-formation in human parotid gland acinar cells.
Abstract
The sodium bicarbonate cotransporter (NBC) protein is functionally expressed in salivary glands. In this experiment, we examined the role of NBC in HCO₃ -formation in human parotid gland acinar cells. Intracellular pH (pHi) was measured in 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) -loaded cells. Acetazolamide (0.1 mM) and 4,4'-diisothio cyanatostilbene-2,2'-disulphonic acid (DIDS, 0.5 mM) were used as specific inhibitors of carbonic anhydrase and NBC, respectively. The degree of inhibition was assessed by measuring the pHi recovery rate (△pHi/min) after cell acidification using an ammonium prepulse technique. In control experiments, △pHi/min was 1.40 ± 0.06. Treatment of cells with 0.5 mM DIDS or 0.1 mM acetazolamide significantly reduced △pH/min to 1.14 ± 0.14 and 0.74 ± 0.15, respectively. Simultaneous application of DIDS and acetazolamide further reduced △ pHi/min to 0.47 ± 0.10. Therefore, DIDS and acetazolamide reduced △pHi/min by 19 % and 47 %, respectively, while simultaneous application of both DIDS and acetazolamide caused a reduction in △pHi/min of 67 %. These results suggest that in addition to carbonic anhydrase, NBC also partially contributes to HCO₃-formation in human parotid gland acinar cells.
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