Involvement of Na+-HCO3- cotransporter in mediating cyclic adenosine 3′,5′-monophosphate-dependent HCO3- secretion by mouse endometrial epithelium

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 (I-SC) technique and intracellular pH measurement. Forskolin stimulated a rise in the 1, 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 I-SC was,obtained when both Cl- and HCO3- in the bath were removed, or in HCO3- -free solution with bumetanide, indicating that the I-SC depended on both Cl- and HCO3-. The presence of the Na+ channel-blocker amiloride in the apical solution did not reduce the forskolin-induced I-SC however, the I-SC could be abolished by removing Na+ from the bathing solution, suggesting that the Cl and HCO3--dependent I-SC was also dependent on basolateral Na+. The forskolin-stimulated I, 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 NaHCO3- 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.