Effects of ouabain and furosemide on basolateral membrane Na efflux of frog skin.

The kinetics of Na tracer fluxes were reinvestigated in isolated epithelia of frog skin in which the unstirred layers of the corium were removed. The rate of appearance of 22Na in the basolateral solution (JNa13) conformed to a single exponential for tracer buildup with a mean t1/2 of 1.9 min. The Na transport pool labeled isotopically from the apical solution was about 40 neq/cm2 for epithelia bathed in either a chloride or sulfate Ringer solution. Basolateral-to-apical solution unidirectional Na flux (JNa31) was low, averaging 0.7 microA/cm2 and remained low for 40 min of ouabain treatment of the epithelia. In agreement with electrophysiological data, ouabain at 10(-4) M caused an acute inhibition (less than 1 min) of the Na efflux at the basolateral membrane (JNa23), falling to 40.6 and 26.7% of control for epithelia bathed in Cl and SO4 Ringer, respectively. Although furosemide exerted little or no consistent effect on the Na flux of control epithelia, this drug in ouabain-poisoned epithelia caused a substantial inhibition of a neutral, chloride-dependent, ouabain-insensitive Na efflux. It is suggested that ouabain "induces" a neutral mechanism of Na transport at the basolateral membrane of the cells that is chloride dependent and furosemide sensitive.