Chloride secretion by canine tracheal epithelium: IV. Basolateral membrane K permeability parallels secretion rate

We evaluated the K conductance properties of the basolateral membranes of the surface cells of canine tracheal epithelium using microelectrode techniques. Studies were conducted under basal conditions (indomethacin, 10(-6) M, mucosal solution) and after stimulation of electrogenic Cl secretion with epinephrine (10(-6) M, serosal solution). Elevated serosal solution [K] depolarized the electrical potential differences across the apical (psi a) and basolateral (psi b) membranes in both the presence and absence of epinephrine. Serosal barium (0.5 mM) also depolarized psi a and psi b and selectively increased basolateral membrane resistance threefold. We also used K-selective microelectrodes to determine cell K activity (acK) and the driving force for K transport across the limiting membranes under basal and stimulated conditions. Stimulation of Cl secretion was not associated with significant changes in psi b or acK so that the driving force for K exit from cell to serosal solution (ca. 20 mV) was not altered. There was close agreement between the basolateral membrane electromotive force (Eb) determined from prior studies (M.J. Welsh, P.L. Smith and R.A. Frizzell, J. Membrane Biol. 71:209-218, 1983) and the chemical potential difference for K across this barrier (EbK) in the presence and absence of epinephrine. These findings support the notion that the basolateral membrane is characterized by a high conductance to K under both secreting and nonsecreting conditions and indicate that the decrease in basolateral membrane resistance that accompanies stimulation of Cl secretion results from an increase in its K conductance. This obviates changes in acK that would otherwise accompany increased Na/K pump activity and, by hyperpolarizing psi a, establishes the electrical driving force for Cl secretion across the apical membrane.