Coupling Asymmetry of Heterotypic Connexin 45/Connexin 43-EGFP Gap Junctions: Properties of Fast and Slow Gating Mechanisms

Although fast and slow gating mechanisms have been described in gap junctions (GJs), their relative contributions to dependence on transjunctional voltage, Vj, is still unclear. We used cell lines expressing wild-type connexin 45 (Cx45) and connexin 43 fused with enhanced green fluorescent protein (...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 99; no. 10; pp. 7113 - 7118
Main Authors:	Bukauskas, Feliksas F., Angele, A. Bukauskiene, Verselis, Vytas K., Michael V. L. Bennett
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 14-05-2002 National Acad Sciences The National Academy of Sciences
Subjects:	Biological Sciences Biology Cell lines Cells Connexin 43 - genetics Connexin 43 - physiology Connexins Connexins - genetics Connexins - physiology Data lines Electric Conductivity Electric current Electric potential Electric pulses Electrical couplings Electrical rectification Electrophysiology Fluorescence Gap junctions Gap Junctions - physiology Green Fluorescent Proteins HeLa Cells Humans Ion Channel Gating - physiology Luminescent Proteins - genetics Luminescent Proteins - physiology Neurology Proteins Recombinant Fusion Proteins - genetics Recombinant Fusion Proteins - physiology Studies
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Summary:	Although fast and slow gating mechanisms have been described in gap junctions (GJs), their relative contributions to dependence on transjunctional voltage, Vj, is still unclear. We used cell lines expressing wild-type connexin 45 (Cx45) and connexin 43 fused with enhanced green fluorescent protein (Cx43-EGFP) to examine mechanisms of gating in homo- and heterotypic GJs formed of these connexins. Macroscopically Cx45/Cx45 channels show high sensitivity to Vj. Cx45 channels demonstrate two types of gating: fast transitions between open and residual states and slow transitions between open and completely closed states. Single-channel conductance of the Cx45 channel is ≈32 pS for the open state and ≈4 pS for the residual state. Cx45/Cx43-EGFP heterotypic junctions exhibit very asymmetrical Vjgating with the maximum junctional conductance shifted to Vjpositive on the Cx45 side. Conductance of single Cx45/Cx43-EGFP channels is ≈55 pS for the open state and ≈4 pS for the residual state, values consistent with the simple-series connection of Cx45 and Cx43-EGFP hemichannels. At Vj= 0, the slow gate of many Cx45 hemichannels is closed in both homotypic Cx45/Cx45 and heterotypic Cx45/Cx43-EGFP junctions. Fast and slow Vjgates of both Cx45 and Cx43 hemichannels close for relative negativity at their cytoplasmic end. Coupling mediated by Cx45/Cx43-EGFP junctions can exhibit asymmetry that can be strongly modulated by small changes in difference of holding potentials. Cx45/Cx43 junctions are likely to be found in brain and heart and may mediate rectifying electrical transmission or modulatable chemical communication.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Contributed by Michael V. L. Bennett To whom reprint requests should be addressed. E-mail: fbukausk@aecom.yu.edu.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.032062099