Insulin action on electrophysiological properties of apical and basolateral membranes of frog skin.

We measured the effects of insulin on the current-voltage (I-V) relations of frog skins impaled with an intracellular microelectrode. The current across the cell membranes was assumed to be equal to the amiloride-inhibitable current. Insulin increased short-circuit current (Isc) approximately 40% from the control value. The increase in Isc was associated with a depolarization of the cell membrane. In addition there was an increase in the value of the parameters that describe the ease of movement of Na+ across the apical membrane, namely, slope conductance (ga), chord conductance (Ga), and permeability (PNa). The values of these parameters show remarkable linear correlations with membrane current both before and after stimulation. Intracellular Na+ activity (acNa) was determined from the I-V relations of the apical membrane. Insulin did not significantly modify acNa. Insulin also increased the value of the basolateral membrane conductance, however, the relationship between this parameter and current was complex. These experiments show that the stimulatory effect of insulin on Isc is associated with an increase in the conductance of both the apical and basolateral membranes.