Single-channel characteristics of a purified bovine renal amiloride-sensitive Na+ channel in planar lipid bilayers.
We have purified an amiloride-inhibitable Na+ channel protein from bovine renal papillae using ion-exchange and immunoaffinity chromatography. In the present study, these purified Na+ channels were reconstituted into planar lipid bilayers, and their single-channel characteristics were studied. We observed both large- and small-conductance Na(+)-selective ion channels in planar lipid bilayers. Single-channel conductance for the large- and small-conductance channels saturated as a function of Na+ concentration. These relations could be fitted by a simple Langmuir isotherm with a Michaelis constant of 55 and 45 mM and a maximum open-state conductance of 56 or 8.4 pS, respectively. Both channels were perfectly cation selective, with a Na(+)-to-K+ permeability ratio of 6.7:1 for the large channel and 7.8:1 for the small channel, and their open single-channel current-voltage relations were linear when bathed with symmetrical Na+ solutions. The percent open time of the reconstituted large or small channels varied between 10 and 50% or 1 and 20%, respectively. After application of amiloride, both the large- and small-conductance Na+ channels were inhibited in a dose-dependent manner.
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
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D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D004553:Electric Conductivity; D007668:Kidney / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism*; D009994:Osmolar Concentration; D010539:Permeability; D015222:Sodium Channels / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology*
D008051:Lipid Bilayers; D015222:Sodium Channels; D000584:Amiloride