Sodium-specific membrane channels of frog skin are pores: current fluctuations reveal high turnover.

The reversible sodium transport blocker amiloride causes current fluctuations at the apical membrane of the outer stratum granulosum of frog skin. Their power density spectra reveal that single transport sites translocate more than 10(6) sodium ions per second, which indicates a pore mechanism. The density of open plus amiloride-blocked pores is in the order of 10(8) pores per square centimeter of skin area with 60 millimolar sodium and 18 micromolar amiloride in the outer solution.