Summary
Bicarbonate is transferred across the serosal (S) membrane of the epithelial cells of the turtle bladder in two directions. Cellular HCO −3 generated behind the H+ pump moves across this membrane into the serosal solution. This efflux of HCO −3 is inhibited by SITS (4-isothiocyano-4′-acetamido-2,2′-disulfonic stilbene). When HCO −3 is added to the serosal solution it is transported across the epithelium in exchange for absorbed Cl−. This secretory HCO −3 flow traverses the serosal cell membrane in the opposite direction. In this study the effects of serosal addition of 5×10−4 m SITS on HCO −3 secretion and Cl− absorption were examined. The rate of H+ secretion was brought to zero by an opposing pH gradient, and 20mm HCO −3 was added toS. HCO −3 secretion, measured by pH stat titration, was equivalent to the increase inM→S Cl− flux after HCO −3 addition. Neither theS→M flux of HCO −3 nor theM→S flux of Cl− were affected by SITS. In the absence of electrochemical gradients, net Cl− absorption was observed only in the presence of HCO −3 in the media; under such conditions, unidirectional and net fluxes of Cl− were not altered by serosal or mucosal SITS. H+ secretion, however, measured simultaneously as the short-circuit current in ouabain-treated bladders decreased markedly after serosal SITS. The inhibition of the efflux of HCO −3 in series with the H+ pump and the failure of SITS to affect HCO −3 secretion and Cl− absorption suggest that the epithelium contains at least two types of transport systems for bicarbonate in the serosal membrane.
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Husted, R.F., Cohen, L.H. & Steinmetz, P.R. Pathways for bicarbonate transfer across the serosal membrane of turtle urinary bladder: Studies with a disulfonic stilbene. J. Membrain Biol. 47, 27–37 (1979). https://doi.org/10.1007/BF01869045
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DOI: https://doi.org/10.1007/BF01869045