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Gap junctions are formed by a family of homologous proteins termed connexins. Their channels are dodecamers, and homomeric forms differ in their properties with respect to control by voltage and other gating stimuli. We report here the properties of coupling from expression of connexin complementary RNAs (cRNAs; sense to mRNA, antisense to cDNA) in Xenopus oocyte pairs in which endogenous coupling was blocked by injection of DNA oligonucleotides antisense to the mRNA of Cx38, the principal endogenous connexin. We found that a connexin recently sequenced from rat liver, Cx26, formed functional gap junctions whose conductance exhibited voltage dependence with unusual characteristics suggestive of two gating mechanisms. Junctional conductance (gj) was increased to a small degree by depolarization and decreased by hyperpolarization of either cell in a coupled pair, indicating dependence on the potential between the inside and outside of the cells (Vi-o). These changes were fast compared with the resolution of their measurement (ca. 10 ms). On a slower timescale, large transjunctional potentials (Vj) of either sign caused a more substantial decrease in conductance similar to that previously reported for several other gap junctions. Homotypic junctions formed of another connexin, Cx32, exhibited a similar slow dependence on Vj but no dependence on Vi-o. In contrast, heterotypic junctions between an oocyte expressing Cx26 and one expressing Cx32 were electrically asymmetric; they exhibited a greater fast change in gj, which depended, however, on Vj, such that gj increased with relative positivity on the Cx26 side and decreased with relative negativity on the Cx26 side. There was also a large slow decrease in gj in response to Vj for relative positivity on the Cx26 side but not for Vj of the opposite sign. These data indicate that properties of the hemichannels contributed by the two connexins in the heterotypic case were changed from their properties in homotypic junctions. The fast change in gj may involve a mechanism analogous to that at fast rectifying electrical synapses. Experiments in which oocytes expressing Cx32 were paired with oocytes expressing both Cx26 and Cx32 demonstrated that asymmetric junctions would form between oocytes expressing both connexins, thereby confirming their potential relevance in vivo, where the same coupled cells are known to express both proteins.
Auerbach,
A rectifying electrotonic synapse in the central nervous system of a vertebrate.
1969, Pubmed
Auerbach,
A rectifying electrotonic synapse in the central nervous system of a vertebrate.
1969,
Pubmed
Barrio,
Gap junctions formed by connexins 26 and 32 alone and in combination are differently affected by applied voltage.
1992,
Pubmed
Bennett,
Gap junctions: new tools, new answers, new questions.
1991,
Pubmed
Beyer,
Connexin43: a protein from rat heart homologous to a gap junction protein from liver.
1987,
Pubmed
Beyer,
Molecular cloning and developmental expression of two chick embryo gap junction proteins.
1990,
Pubmed
Dahl,
Expression of functional cell-cell channels from cloned rat liver gap junction complementary DNA.
1987,
Pubmed
,
Xenbase
Dermietzel,
Differential expression of three gap junction proteins in developing and mature brain tissues.
1989,
Pubmed
Ebihara,
Cloning and expression of a Xenopus embryonic gap junction protein.
1989,
Pubmed
,
Xenbase
Fishman,
Functional analysis of human cardiac gap junction channel mutants.
1991,
Pubmed
Gimlich,
Differential regulation of the levels of three gap junction mRNAs in Xenopus embryos.
1990,
Pubmed
,
Xenbase
Harris,
Kinetic properties of a voltage-dependent junctional conductance.
1981,
Pubmed
Hoh,
Molecular cloning and characterization of a new member of the gap junction gene family, connexin-31.
1991,
Pubmed
,
Xenbase
Lash,
Cloning of a gap junctional protein from vascular smooth muscle and expression in two-cell mouse embryos.
1990,
Pubmed
Margiotta,
Conductance and dye permeability of a rectifying electrical synapse.
,
Pubmed
Methfessel,
Patch clamp measurements on Xenopus laevis oocytes: currents through endogenous channels and implanted acetylcholine receptor and sodium channels.
1986,
Pubmed
,
Xenbase
Moreno,
Voltage-dependent gap junction channels are formed by connexin32, the major gap junction protein of rat liver.
1991,
Pubmed
Nicholson,
Two homologous protein components of hepatic gap junctions.
,
Pubmed
Obaid,
Cell-to-cell channels with two independently regulated gates in series: analysis of junctional conductance modulation by membrane potential, calcium, and pH.
1983,
Pubmed
Paul,
Molecular cloning of cDNA for rat liver gap junction protein.
1986,
Pubmed
Reverdin,
Electrical properties of the gap junctional membrane studied in rat liver cell pairs.
1988,
Pubmed
Ringham,
Localization and electrical characteristics of a giant synapse in the spinal cord of the lamprey.
1975,
Pubmed
Rook,
Single channel currents of homo- and heterologous gap junctions between cardiac fibroblasts and myocytes.
1989,
Pubmed
Shiosaka,
Gap junction protein in rat hippocampus: correlative light and electron microscope immunohistochemical localization.
1989,
Pubmed
Spray,
Gating of gap junction channels.
1984,
Pubmed
Spray,
Equilibrium properties of a voltage-dependent junctional conductance.
1981,
Pubmed
,
Xenbase
Spray,
Isolated liver gap junctions: gating of transjunctional currents is similar to that in intact pairs of rat hepatocytes.
1986,
Pubmed
Swenson,
Formation of gap junctions by expression of connexins in Xenopus oocyte pairs.
1989,
Pubmed
,
Xenbase
Traub,
Comparative characterization of the 21-kD and 26-kD gap junction proteins in murine liver and cultured hepatocytes.
1989,
Pubmed
Verselis,
A voltage-dependent gap junction in Drosophila melanogaster.
1991,
Pubmed
Werner,
Formation of hybrid cell-cell channels.
1989,
Pubmed
,
Xenbase
Zhang,
Sequence and tissue distribution of a second protein of hepatic gap junctions, Cx26, as deduced from its cDNA.
1989,
Pubmed