Role of basolateral membrane conductance in the regulation of transepithelial sodium transport across frog skin

Circuit analyses of the principal cell compartment of frog skin (Rana temporaria and R. esculenta) were made using microelectrode measurements under short-circuit conditions and with the aid of the Na+ channel blocker amiloride. Under control conditions, intracellular potential ranged between −65 and −5 mV, and the conductances of the apical and basolateral membranes were related directly to the short-circuit current and inversely to the cellular potential. Blockade of apical Na+ uptake by amiloride hyperpolarized the cells to nearly the same value, irrespective of the potential under transporting conditions. Under these conditions, basolateral membrane conductance increased greatly, which led to paradoxical reactions of the transepithelial Na+ transport at lower concentrations of amiloride. The half-maximal inhibitory concentration of amiloride estimated from the response of the apical membrane conductance (99±10 nM) was about 5 times lower than the value derived from transepithelial current or conductance in the same tissues. The results are discussed in the context of the importance of the membrane potential for acute control of membrane conductance and transepithelial transport.