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. 1997 Mar;72(3):1182–1192. doi: 10.1016/S0006-3495(97)78766-6

Mechanosensitivity of an epithelial Na+ channel in planar lipid bilayers: release from Ca2+ block.

I I Ismailov 1, B K Berdiev 1, V G Shlyonsky 1, D J Benos 1
PMCID: PMC1184502  PMID: 9138565

Abstract

A family of novel epithelial Na+ channels (ENaCs) have recently been cloned from several different tissues. Three homologous subunits (alpha, beta, gamma-ENaCs) from the core conductive unit of Na(+)-selective, amiloride-sensitive channels that are found in epithelia. We here report the results of a study assessing the regulation of alpha,beta,gamma-rENaC by Ca2+ in planar lipid bilayers. Buffering of the bilayer bathing solutions to [Ca2+] < 1 nM increased single-channel open probability by fivefold. Further investigation of this phenomenon revealed that Ca2+ ions produced a voltage-dependent block, affecting open probability but not the unitary conductance of ENaC. Imposing a hydrostatic pressure gradient across bilayers containing alpha,beta,gamma-rENaC markedly reduced the sensitivity of these channels to inhibition by [Ca2+]. Conversely, in the nominal absence of Ca2+, the channels lost their sensitivity to mechanical stimulation. These results suggest that the previously observed mechanical activation of ENaCs reflects a release of the channels from block by Ca2+.

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Selected References

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