Determination of the ENa of from skin from studies of its current-voltage relationship

Studies were done to test the idea that the emf of the sodium pump (ENa) of isolated frog skin could be estimated directly from studies of its current-voltage relationship. ENa was estimated in two ways: a) from the bidirectional sodium flux ratio according to Ussing and Zerahn, and b) from the values of open-circuit voltage, short-circuit current, and the shunt resistance estimated when the [Na] of the outer solution was reduced to zero. When the values of ENa were compared with the values of E1 obtained from the current-voltage relationships, they were found to be the same despite considerable variability in the values of ENa between skins (77-168 mV). In general, the values of ENa were considerably higher when the skins were bathed with sulfate-Ringer as compared with chloride-Ringer solution. These data are compatible with the idea that in nonedge-damaged frog skin, the unidirectional sodium fluxes were confined primarily to active transport pathways alone, and, accordingly, they may be excluded from parallel-shunt pathways.