title: Properties of single- and double-barreled Cl channels of shark rectal gland in planar bilayers.
abstract: Chloride channels from the apical plasma membrane fraction of rectal gland of Squalus acanthias were characterized by incorporation into planar bilayers in the presence of cAMP-PK/ATP. In a total of 80 bilayer preparations, 21 Cl-selective channels were observed as single channels and 13 as pairs. This was a significantly greater number of double Cl channels than expected from a binomial distribution. The double Cl channels were divided into two groups based on kinetic and voltage-dependent behavior. One group had properties identical to the single channels (gb1) while the other was consistent with a double-barreled channel (gb2) with coordinated activity between proto-channels. The single-channel slope conductances of gb1 and gb2 from -60 to +20 mV with a 250/70 mM KCl gradient were 41 and 75 pS, respectively. With symmetrical 250 mM KCl, the I-V relation of gb1 showed outward rectification with 47.8 +/- 6.6 pS at cis negative potentials and 68.9 +/- 6.1 pS at cis positive potentials. gb1 was open from 70 to 95% at all electrochemical potentials from -80 to +40 mV. gb2 was steeply voltage dependent between -80 and -20 mV. Both gb1 and gb2 were insensitive to Ca (from 100 nm to 1 microM), blocked by 0.1 mM DIDS and highly selective for chloride. These data suggest that double-barreled Cl channels are related to the family of small, outwardly rectifying Cl channels of epithelial membranes.
authors.affiliation: Department of Medicine, University of Texas Medical School, Houston 77225.
authors.forename: S C
authors.initials: SC
authors.lastname: Sansom
authors.forename: S L
authors.initials: SL
authors.lastname: Carosi
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability / Q000502:physiology; D002712:Chlorides / Q000493:pharmacokinetics*; D004284:Dogfish / Q000502:physiology*; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D008051:Lipid Bilayers / Q000032:analysis*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D012491:Salt Gland / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D002712:Chlorides; D007473:Ion Channels; D008051:Lipid Bilayers; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid