The present study investigated the involvement of Na -HCO3− cotransporter in mediating cAMP-stimulated HCO3− secretion across the cultured mouse endometrial epithelium using the short-circuit current (ISC) technique and intracellular pH measurement. Forskolin stimulated a rise in the ISC, 55.6% and 52.1% of which could be reduced by the removal of extracellular Cl− or by eliminating the contribution of Cl− secretion by bumetanide, an inhibitor of Na -K -2Cl− cotransporter, respectively. More than 80% reduction in the forskolin-induced ISC was obtained when both Cl− and HCO3− in the bath were removed or in HCO3−-free solution with bumetanide, indicating that the ISC depended on both Cl− and HCO3−. The presence of the Na channel-blocker amiloride in the apical solution did not reduce the forskolin-induced ISC; however, the ISC could be abolished by removing Na from the bathing solution, suggesting that the Cl−- and HCO3−-dependent ISC was also dependent on basolateral Na . The forskolin-stimulated ISC could be reduced 43.6% by removal of HCO3− and 47.9% by a Na -HCO3−-cotransporter inhibitor, dihydrogen-4,4′-didsothiocyanostilbene-2,2′-disulfonic acid (H2DIDS). The inhibitory effect of H2DIDS was observed in Cl−-free solution, but not when HCO3− was removed, thus confirming its effect on HCO3−-dependent transport. Intracellular pH measurements demonstrated that the recovery from cellular acidification depended on the presence of both basolateral Na and HCO3−, further indicating the involvement of Na -HCO3− cotransporter. Reverse transcription-polymerase chain reaction experiments confirmed the expression of Na -HCO3− cotransporter in the mouse endometrium. The results suggest that basolaterally located Na -HCO3− cotransporter is involved in mediating cAMP-stimulated HCO3− secretion across the mouse endometrial epithelium.
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