Effects of biguanides on short-circuit current in frog skin.

The addition of phenformin to the solution bathing the mucosal side of frog skin resulted in a sustained stimulation of short-circuit current accompanied by an increase in open-circuit potential and total conductance of the membrane. The flux of 22Na from the mucosal to the serosal side of the skin was increased by phenformin, whereas no significant effect on the flux from the serosal to the mucosal side was observed. The increases in the short-circuit current and total conductance with phenformin were completely abolished by the addition of 5 X 10(-5) M amiloride, which blocks sodium permeability at the apical surface of the membrane. Thus, the stimulation of active sodium transport in frog skin by phenformin would be due to the increase in the amiloride-sensitive sodium permeability of the membrane. Phenformin may prove to be a useful tool for the study of sodium transport in amphibian epithelia.