title: Evidence from incorporation and patch-clamp experiments for a nonselective channel of large conductance at the luminal membrane of rabbit proximal tubule.
abstract: The presence of nonselective ionic channels at the apical membrane of rabbit proximal tubule cells was investigated by fusion of proximal tubule brush border membrane vesicles onto a planar bilayer and by means of patch clamp measurements on primary cultured proximal tubule cells. The fusion of brush border membrane vesicles onto a phosphatidylethanolamine-phosphatidylcholine (1:1) planar bilayer led to the identification of a nonselective channel of 115 pS in 200 mM NaCl conditions with an ionic permeability sequence for Na+, K+, and Cl- corresponding to PNa/PK = 0.3 and PNa/PCl = 3, respectively. This channel showed an increased open probability at depolarizing potentials, but its activity was independent of the Ca2+ concentration in both the cis and trans compartments. These findings were subsequently confirmed in inside-out patch clamp experiments carried out on primary cultured proximal tubule cells. This channel was seldom seen in cell-attached recordings on resting cells, but its presence was observed with a higher probability in patch excised experiments performed following superfusion of the cells with a hypotonic solution. It is suggested on the basis of these observations that the apical membrane of rabbit proximal tubule cells contains a voltage-dependent nonselective channel, the activity of which may contribute to the regulation of the membrane potential.
authors.affiliation: Département de physiologie, Faculté de médicine, Université de Montréal, QC, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Bellemare
authors.forename: L
authors.initials: L
authors.lastname: Dubé
authors.forename: R
authors.initials: R
authors.lastname: Sauvé
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D007687:Kidney Tubules, Proximal / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000502:physiology; D008871:Microvilli / Q000201:enzymology / Q000502:physiology; D018408:Patch-Clamp Techniques; D011817:Rabbits
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D002118:Calcium