Na+ channels and amiloride-induced noise in the mammalian colon epithelium.

(1) The effects of the Na+-channel blocker, amiloride, on the short-circuit current carried by Na+ was studied with fluctuation analysis, in rabbit descending colon epithelium. (2) In the presence of mucosal amiloride, the power spectrum of the Na+-current noise showed a Lorentzian component. When the Na+ current was reduced by increasing the blocker concentrations, the Lorentzian plateau decreased and corner frequency increased. Macroscopic short-circuit current and current-noise data are evidence for a two-state mechanism of the blocker interaction with the Na+ channel. (3) On- and off-rate constants for the blocker-receptor reaction, single-channel currents and Na+-channel density were calculated at room temperature and at 37 degrees C. Also, the activation energy for the amiloride-receptor reaction was estimated. The microscopic parameters obtained for the Na+ channel in the colon were similar to those found for Na+ channels in other tight epithelia.