title: Evidence from incorporation experiments for an anionic channel of small conductance at the apical membrane of the rabbit distal tubule.
abstract: Many of the hormone-regulated ion transport processes in distal nephron involve transcellular pathways which require a passive entry of ions at the apical membrane of the distal tubule cells. To investigate molecular mechanisms underlying the ionic permeability of the distal tubule apical membrane, a study was undertaken in which vesicles prepared from apical membranes from isolated rabbit distal tubules were fused onto a planar lipid bilayer. These experiments led to the identification of several ionic channels including a Cl(-)-permeable channel of 14 pS with a Na+ over Cl- permeability ratio, PNa/PCl < 0.09. The open channel probability (Po) showed a weak voltage dependency with Po increasing slightly at negative potential values (intracellular (trans) relative to extracellular (cis) for right-side-out vesicles). Channel activity was inhibited by NPPB at high concentrations (> 100 microM) and by DIDS (300 microM). A small inhibitory effect was also observed in the presence of DPC at concentrations ranging from 200 microM to 500 microM. The presence of SO4(2-) (32 mmol/l) in the trans solution caused a complete inhibition of channel activity, but no modification of channel behaviour was observed with the non-selective channel blocking agent gadolinium (Gd3+) at 100 microM. Finally, addition of the catalytic subunit of protein kinase A into the trans chamber (60 U/ml to 80 U/ml) led to an increase in channel activity characterized by a greater number of active channels coupled to an increase of the individual channel open probability. The action of the protein kinase A could be cancelled by the addition of a non specific protein phosphatase, such as alkaline phosphatase. Our results suggest that the apical membrane of the rabbit distal tubule contains a Cl- permeable channel of small conductance the activity of which may be modulated by hormones linked to the adenylate cyclase pathway.
authors.affiliation: Department of Physiology, University of Montreal, Quebec, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Denicourt
authors.forename: S
authors.initials: S
authors.lastname: Cai
authors.forename: L
authors.initials: L
authors.lastname: Garneau
authors.forename: M G
authors.initials: MG
authors.lastname: Brunette
authors.forename: R
authors.initials: R
authors.lastname: Sauvé
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000494:pharmacology; D004594:Electrophysiology; D005682:Gadolinium / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism*; D007686:Kidney Tubules, Distal / Q000737:chemistry*; D008051:Lipid Bilayers / Q000378:metabolism; D009579:Nitrobenzoates / Q000494:pharmacology; D010539:Permeability; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013431:Sulfates / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008051:Lipid Bilayers; D009579:Nitrobenzoates; D010743:Phospholipids; D013431:Sulfates; D062367:ortho-Aminobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; C001209:fenamic acid; D012964:Sodium; D005682:Gadolinium; D017868:Cyclic AMP-Dependent Protein Kinases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium