Correlative Studies of Gating in Cx46 and Cx50 Hemichannels and Gap Junction Channels

¹ SUNY State College of Optometry
² Albert Einstein College of Medicine

^* To whom correspondence should be addressed. E-mail: verselis{at}aecom.yu.edu.

Submitted on October 7, 2004
Revised on November 9, 2004
Accepted on 29 November 2004

	Abstract

Transjunctional voltage (Vj) gating of gap junction (GJ) channels has been proposed to occur by gating of the component hemichannels. We took advantage of the ability of Cx46 and Cx50 to function as unapposed hemichannels to identify gating properties intrinsic to hemichannels and how they contribute to gating of GJ channels. We show that Cx46 and Cx50 hemichannels contain two distinct gating mechanisms that generate reductions in macroscopic and single channel currents for both membrane polarities. At positive voltages, gating is similar in Cx46 and Cx50 hemichannels, primarily showing transitions to long-lived substates. At negative voltages, Cx46 currents deactivate completely and the underlying single hemichannels exhibit transitions to a fully closed state. In contrast, Cx50 currents do not deactivate completely at negative voltages and the underlying single hemichannels predominantly exhibit transitions to various substates. Transitions to a fully closed state occur, but are infrequent. In the respective GJ channels, both forms of gating contribute to the reduction in conductance by Vj. However, examination of gating of mutant hemichannels and GJ channels in which the Asp at position 3 was replaced with Asn (D3N) showed that the positive hemichannel gate predominantly closes Cx50 GJs whereas the negative hemichannel gate predominantly closes Cx46 GJs in response to Vj. We also report, for the first time, single Cx50 hemichannels in oocytes are inwardly rectifying, high conductance channels ( = 470 pS). The antimalarial drug mefloquine, which selectively blocks Cx50 and not Cx46 GJs, shows the same selectivity in Cx50 and Cx46 hemichannels indicating that the actions of such uncoupling agents, like voltage gating, are intrinsic hemichannel properties.

Key Words: Xenopus oocytes, connexin, intercellular communication, mefloquine, single channels, voltage dependence

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