title: Ionic blockade of the rat connexin40 gap junction channel by large tetraalkylammonium ions.
abstract: The rat connexin40 gap junction channel is permeable to monovalent cations including tetramethylammonium and tetraethylammonium ions. Larger tetraalkyammonium (TAA(+)) ions beginning with tetrabutylammonium (TBA(+)) reduced KCl junctional currents disproportionately. Ionic blockade by tetrapentylammonium (TPeA(+)) and tetrahexylammonium (THxA(+)) ions were concentration- and voltage-dependent and occurred only when TAA(+) ions were on the same side as net K(+) efflux across the junction, indicative of block of the ionic permeation pathway. The voltage-dependent dissociation constants (K(m)(V(j))) were lower for THxA(+) than TPeA(+), consistent with steric effects within the pore. The K(m)-V(j) relationships for TPeA(+) and THxA(+) were fit with different reaction rate models for a symmetrical (homotypic) connexin gap junction channel and were described by either a one- or two-site model that assumed each ion traversed the entire V(j) field. Bilateral addition of TPeA(+) ions confirmed a common site of interaction within the pore that possessed identical K(m)(V(j)) values for cis-trans concentrations of TPeA(+) ions as indicated by the modeled I-V relations and rapid channel block that precluded unitary current measurements. The TAA(+) block of K(+) currents and bilateral TPeA(+) interactions did not alter V(j)-gating of Cx40 gap junctions. N-octyl-tributylammonium and -triethylammonium also blocked rCx40 channels with higher affinity and faster kinetics than TBA(+) or TPeA(+), indicative of a hydrophobic site within the pore near the site of block.
authors.affiliation: Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210, USA.
authors.forename: H
authors.initials: H
authors.lastname: Musa
authors.forename: J D
authors.initials: JD
authors.lastname: Gough
authors.forename: W J
authors.initials: WJ
authors.lastname: Lees
authors.forename: R D
authors.initials: RD
authors.lastname: Veenstra
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D017630:Connexins / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D017629:Gap Junctions / Q000737:chemistry*; D007477:Ions; D007700:Kinetics; D051379:Mice; D008956:Models, Chemical; D008962:Models, Theoretical; D011188:Potassium / Q000737:chemistry; D011485:Protein Binding; D000644:Quaternary Ammonium Compounds / Q000737:chemistry* / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D000097003:Gap Junction alpha-5 Protein
chemical_list: D002118:Calcium; D017630:Connexins; D007477:Ions; D011188:Potassium; D000644:Quaternary Ammonium Compounds; D000097003:Gap Junction alpha-5 Protein; C066585:triethylammonium cation