title: Biochemical status of renal epithelial Na+ channels determines apparent channel conductance, ion selectivity, and amiloride sensitivity.
abstract: Purified bovine renal papillary Na+ channels, when reconstituted into planar lipid bilayers, reside in three conductance states: a 40-pS main state, and two subconductive states (12-13 pS and 24-26 pS). The activity of these channels is regulated by phosphorylation and by G-proteins. Protein kinase A (PKA)-induced phosphorylation increased channel activity by increasing the open state time constants from 160 +/- 30 (main conductance), and 15 +/- 5 ms (both lower conductances), respectively, to 365 +/- 30 ms for all of them. PKA phosphorylation also altered the closed time of the channel from 250 +/- 30 ms to 200 +/- 35 ms, thus shifting the channel into a lower-conductance, long open time mode. PKA phosphorylation increased the PNa:PK of the channel from 7:1 to 20:1, and shifted the amiloride inhibition curve to the right (apparent K(i)amil from 0.7 to 20 microM). Pertussis toxin-induced ADP-ribosylation of either phosphorylated of either phosphorylated or nonphosphorylated channels decreased the PNa:PK to 2:1 and 4:1, respectively, and altered K(i)amil to 8 and 2 microM for phosphorylated and nonphosphorylated channels, respectively. GTP-gamma-S treatment of either phosphorylated or nonphosphorylated channels resulted in an increase of PNa:PK to 30:1 and 10:1, respectively, and produced a leftward shift in the amiloride dose-response curve, altering K(i)amil to 0.5 and 0.1 microM, respectively. These results suggest that amiloride-sensitive renal Na+ channel biophysical characteristics are not static, but depend upon the biochemical state of the channel protein and/or its associated G-protein.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham 35294, USA.
authors.forename: I I
authors.initials: II
authors.lastname: Ismailov
authors.forename: B K
authors.initials: BK
authors.lastname: Berdiev
authors.forename: D J
authors.initials: DJ
authors.lastname: Benos
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004351:Drug Resistance; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000584:Amiloride; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins