Patch clamp studies of apical membranes of renal cortical collecting ducts

Abstract

Patch clamp techniques were used in study of the apical membrane of isolated renal cortical collecting ducts. Whereas on-the-cell patches (reported previously) gave channel activity due primarily to K+, isolated inside-out patches of the same membranes bathed with 150 mM Na+, 5 mM K+, and 1 mM Ca2+ gave channel activity due primarily to Na+. Na+ channels could remain either open or closed for periods of milliseconds to minutes. Although unitary currents of tenths of a pA were observed routinely, patch activity could change spontaneously between quiescent and violent with 'apparent' unitary currents of several pA. It was not possible to rule out the idea that the complex activity of the patches was due to synchronous or near synchronous openings/closings of several channels of identical unitary current. The unpredictable spontaneous changes of patch activity make difficult the design of experiments to test for the influence of agents expected or suspected to alter channel behavior.

Blocker-related changes of channel density. Analysis of a three-state model for apical Na channels of frog skin.

“…Patch-clamp experiments indicate unequivocally that highly selective epithelial Na channels fluctuate spontaneously between closed and open states with rather long mean open and closed times of several to many seconds (Sariban-Sohraby et al, 1984;Helman et al, 1985;Palmer and Frindt, 1986;Eaton and Hamilton, 1988;Marunaka Y., and D. C. Eaton, personal communication iO0 tO00 Frequency (Hz) FIGURE 2. Power density spectra of a short-circuited epithelium in the absence (A) and presence of apical 5 pM (B) and 50 #M (C) CDPC.…”