Extracellular Zn2+ activates epithelial Na+ channels by eliminating Na+ self-inhibition.
Inhibition of epithelial Na(+) channel (ENaC) activity by high concentrations of extracellular Na(+) is referred to as Na(+) self-inhibition. We investigated the effects of external Zn(2+) on whole cell Na(+) currents and on the Na(+) self-inhibition response in Xenopus oocytes expressing mouse alphabetagamma ENaC. Na(+) self-inhibition was examined by analyzing inward current decay from a peak current to a steady-state current following a fast switching of a low Na(+) (1 mm) bath solution to a high Na(+) (110 mm) solution. Our results indicate that external Zn(2+) rapidly and reversibly activates ENaC in a dose-dependent manner with an estimated EC(50) of 2 microm. External Zn(2+) in the high Na(+) bath also prevents or reverses Na(+) self-inhibition with similar affinity. Zn(2+) activation is dependent on extracellular Na(+) concentration and is absent in ENaCs containing gammaH239 mutations that eliminate Na(+) self-inhibition and in alphaS580Cbetagamma following covalent modification by a sulfhydryl-reactive reagent that locks the channels in a fully open state. In contrast, external Ni(2+) inhibition of ENaC currents appears to be additive to Na(+) self-inhibition when Ni(2+) is present in the high Na(+) bath. Pretreatment of oocytes with Ni(2+) in a low Na(+) bath also prevents the current decay following a switch to a high Na(+) bath but rendered the currents below the control steady-state level measured in the absence of Ni(2+) pretreatment. Our results suggest that external Zn(2+) activates ENaC by relieving the channel from Na(+) self-inhibition, and that external Ni(2+) mimics or masks Na(+) self-inhibition.
Sheng
Shaohu
S
Renal-Electrolyte Division, Department of Medicine, School of Medicine, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, Pennsylvania 15261, USA. shaohu@pitt.edu
Perry
Clint J
CJ
Kleyman
Thomas R
TR
D000818:Animals; D053503:Epithelial Sodium Channels; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009532:Nickel / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology*
D053503:Epithelial Sodium Channels; D011994:Recombinant Proteins; D015222:Sodium Channels; D009532:Nickel; D012964:Sodium; D015032:Zinc