Na self inhibition of human epithelial Na channel: temperature dependence and effect of extracellular proteases.
The regulation of the open probability of the epithelial Na(+) channel (ENaC) by the extracellular concentration of Na(+), a phenomenon called "Na(+) self inhibition," has been well described in several natural tight epithelia, but its molecular mechanism is not known. We have studied the kinetics of Na(+) self inhibition on human ENaC expressed in Xenopus oocytes. Rapid removal of amiloride or rapid increase in the extracellular Na(+) concentration from 1 to 100 mM resulted in a peak inward current followed by a decline to a lower quasi-steady-state current. The rate of current decline and the steady-state level were temperature dependent and the current transient could be well explained by a two-state (active-inactive) model with a weakly temperature-dependent (Q(10)act = 1.5) activation rate and a strongly temperature-dependant (Q(10)inact = 8.0) inactivation rate. The steep temperature dependence of the inactivation rate resulted in the paradoxical decrease in the steady-state amiloride-sensitive current at high temperature. Na(+) self inhibition depended only on the extracellular Na(+) concentration but not on the amplitude of the inward current, and it was observed as a decrease of the conductance at the reversal potential for Na(+) as well as a reduction of Na(+) outward current. Self inhibition could be prevented by exposure to extracellular protease, a treatment known to activate ENaC or by treatment with p-CMB. After protease treatment, the amiloride-sensitive current displayed the expected increase with rising temperature. These results indicate that Na(+) self inhibition is an intrinsic property of sodium channels resulting from the expression of the alpha, beta, and gamma subunits of human ENaC in Xenopus oocyte. The extracellular Na(+)-dependent inactivation has a large energy of activation and can be abolished by treatment with extracellular proteases.
Chraïbi
Ahmed
A
Institut de Pharmacologie et de Toxicologie, CH-1005 Lausanne, Switzerland.
Horisberger
Jean-Daniel
JD
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053503:Epithelial Sodium Channels; D005110:Extracellular Space / Q000378:metabolism*; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D006706:Homeostasis; D006801:Humans; D008954:Models, Biological; D009675:Novobiocin / Q000494:pharmacology; D009865:Oocytes; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013696:Temperature; D014357:Trypsin / Q000494:pharmacology; D014982:Xenopus laevis; D020245:p-Chloromercuribenzoic Acid / Q000494:pharmacology
D001562:Benzimidazoles; D004791:Enzyme Inhibitors; D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D013439:Sulfhydryl Reagents; D009675:Novobiocin; D020245:p-Chloromercuribenzoic Acid; D006147:Guanine; D000584:Amiloride; D012964:Sodium; D010450:Endopeptidases; D014357:Trypsin