Mechanosensitivity of an epithelial Na+ channel in planar lipid bilayers: release from Ca2+ block.
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+.
Ismailov
I I
II
Department of Physiology and Biophysics, University of Alabama at Birmingham 35294, USA.
Berdiev
B K
BK
Shlyonsky
V G
VG
Benos
D J
DJ
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004285:Dogs; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D015640:Ion Channel Gating; D007700:Kinetics; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D008861:Microsomes / Q000378:metabolism; D008956:Models, Chemical; D018408:Patch-Clamp Techniques; D014176:Protein Biosynthesis; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D015222:Sodium Channels / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*
D008051:Lipid Bilayers; D046911:Macromolecular Substances; D015222:Sodium Channels; D000584:Amiloride; D002118:Calcium