Biophysical properties of mouse connexin30 gap junction channels studied in transfected human HeLa cells

Abstract

Our knowledge on functional aspects of gap junction channels has evolved quickly over the last decade. Progress has been closely associated with the availability of cDNAs coding for various gap junction proteins of vertebrates, the connexins. Expression studies with injected Xenopus oocytes and transfected mammalian cells have shown that the functional diversity of gap junctions reflects the structural variety of connexins (see Bruzzone et al. 1996). Recently, a new mouse connexin has been identified and cloned by screening of a mouse genomic library (Dahl et al. 1996). This protein has a molecular mass of 30•366 kDa and hence was called connexin30 (Cx30). Northern blots of total RNA from mouse tissues have indicated that Cx30 is strongly expressed in adult brain as well as skin and is less abundant in uterus, lung and eye tissue. Small amounts of transcripts have been detected in testis and sciatic nerve. No Cx30 mRNA has been found in liver. Sequence comparisons of nucleotides and amino acids suggest that mouse Cx30 is a close relative of mouse Cx26. There are few reports in the literature on functional aspects of Cx30 gap junctions. Injection of mouse Cx30 cRNA into Xenopus oocytes induced the formation of gap junctions susceptible to intercellular current flow and dye diffusion (Dahl et al. 1996). Neurobiotin diffusion experiments with transfected HeLa cells revealed that Cx30 forms heterotypic gap junction channels with Cx26, Cx30•3, Cx31, Cx40, Cx43, Cx45 and Cx50 (D. Manthey et al., in preparation). Electrophysiological studies on pairs of transfected HeLa

Functional Role of the Carboxyl Terminal Domain of Human Connexin 50 in Gap Junctional Channels

“…Furthermore, when such transitions did occur, their duration was long (>2 msec). Mouse Cx30, Cx40 and Cx43 gap junctional channels have also been reported to exhibit a residual conductance state (Bukauskas et al, 1995;Valiunas et al, 1999;Banach & Weingart, 2000). The behavior of human Cx50 gap junctional channels differs from that described by Weingart et al (1993) in several respects.…”

New roles for astrocytes: Gap junction hemichannels have something to communicate

“…In the five connexins for which such data are available, the open hemichannel conductance is close to twice the open cellcell channel conductance, as would follow from simple series connection [4,22,[42][43][44][45][46][47] ( Table 1, Figure 1). The same conclusion has been reached for several connexins that form heterotypic junctions: the heterotypic channel conductance was the series sum of the inferred hemichannel conductances (twice the single channel conductance of the homotypic junctions [47][48][49]).…”

Connexin and pannexin hemichannels of neurons and astrocytes

“…53 In HeLa cells, expressed Cx30 gap junctions had properties expected of members of this family of proteins. There were two conductance states (179 and 48 pS) and a strong dependence upon junctional voltage with a half voltage of inactivation of ±27 mV 7 (Table 1). Cx30 hemichannels have also been studied in the oocyte expression system and wild type channels did not form functional hemichannels at depolarized potentials; however the effect of removing extracellular divalent ions on channel activation was not tested.…”

“…This is due to binding of calcium to an extracellular domain, phosphorylation on intracellular serine/ threonine residues, and a voltage-dependence that is not favorable to hemichannel opening near resting membrane potentials. [3][4][5][6][7][8] However, recent evidence suggests that hemichannels can be opened in a regulated manner during physiological events, as well as unregulated (or irreversible) opening during pathological situations, [9][10][11][12] but the contributions of Cx hemichannels to physiological events remain contentious.…”