title: Ca(2+)-induced down-regulation of epithelial amiloride-sensitive channels reconstituted into planar lipid bilayers.
abstract: Multichannel experiments were carried out to investigate the Ca(2+)-induced down-regulation of epithelial Na+ channels reconstituted into planar lipid bilayer membranes. Reconstitution was achieved by fusion of vesiculated apical membrane fragments to solvent-free planar lipid bilayers. We found that the presence of micromolar concentrations of Ca2+ on the side to which the vesicles were added substantially lowered the channel-mediated current. The inhibition was strongly influenced by pH. At pH 8.0, all the current was blocked by 1 mM calcium, whereas at pH 7.1 the inhibition was about 80%. The blocking kinetics was clearly voltage-dependent. The mechanism of blocking cannot be explained either in terms of interactions with a single site, or by a model in which two blocking sites are assumed.
authors.affiliation: Departamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brasil.
authors.forename: L G
authors.initials: LG
authors.lastname: Siqueira-Branco
authors.forename: W A
authors.initials: WA
authors.lastname: Varanda
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002024:Bufo marinus; D002118:Calcium / Q000502:physiology*; D002463:Cell Membrane Permeability; D015536:Down-Regulation; D012867:Skin / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism
chemical_list: D015222:Sodium Channels; D000584:Amiloride; D002118:Calcium