MECHANISMS OF SODIUM AND CHLORIDE TRANSPORT ACROSS ISOLATED SHEEP RETICULUM

1. Na-22+ and Cl-36- fluxes across isolated reticular epithelium of sh eep were measured by using the Ussing-chamber technique. 2. Net NaCl a bsorption driven by Na+-K+-ATPase was observed under short-circuit con ditions. 3. Evaluation of fluxes measured under voltage-clamp conditio ns indicated that Na+ absorption is mainly electroneutral. 4. Mucosal application of bumetanide, hydrochlorothiazide, or low dose amiloride (10(-4) M+ produced no changes in Na+ transport whereas addition of hi gher doses of amiloride (greater-than-or-equal-to 10(-3) M) led to a r eduction in net Na+ transport. Short chain fatty acids (SCFA) enhanced the amiloride-sensitive Na+ transport. 5. Alterations of J(ms)Na indu ced by inhibitors or by SCFA were always accompanied by qualitatively similar changes of J(sm)Na. Amiloride-sensitive J(sm)Na was also decre ased at low mucosal Na+ concentration. 6. DIDS, SITS, and nitrate redu ced both J(ms)Cl and J(sm)Cl. SCFA did not influence chloride transpor t. 7. It is concluded that Na+ transport is mediated by Na+-H+ exchang e and by transport processes operating as Na+ self-exchange. Mucosal-t o-serosal chloride transport seems partly to depend on anion exchange systems.