Coupled active transport of Na and Cl across forestomach epithelium
Chien, W.J.; Stevens, C.E.
American Journal of Physiology 223(4): 997-1003
1972
ISSN/ISBN: 0002-9513 PMID: 5075173 Document Number: 44556
Bidirectional fluxes of Na and Cl across isolated, short-circuited bovine rumen epithelium were measured by double and quadruple isotope-labelling techniques. Both Na and Cl were actively transported in the direction of lumen to blood, but since Cl was transported at approximately twice the rate of Na, the algebraic sum of their ion currents did not account for the recorded short-circuit current or even the sign (blood side positive) of the transepithelial electrical potential. Ion replacement experiments indicated that active transport of K or multivalent inorganic ions could not account for this discrepancy. Removal of Cl from the bathing solution reduced active Na transport to levels which could entirely account for the short-circuit current. Alternatively, removal of the Na from the solutions almost completely inhibited the short-circuit and notably inhibited the active transport of Cl. Replacement of the bicarbonate buffer system with tricine significantly reduced active transport of both Na and Cl. Results indicated that a substantial active transport of at least 3 ions was required to explain the observed short-circuit current, the additional ion(s) were HCO3- and possibly H+, and the active transport of these ions was coupled to a significant degree.