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Subconductance States of Cx30 Gap Junction Channels: Data from Transfected HeLa Cells versus Data from a Mathematical Model

Rolf Vogel ^*, Virginijus Valiunas  and Robert Weingart 

^* Department of Cardiology, University Hospital Bern, Bern, Switzerland; and Institute of Physiology, University of Bern, Bern, Switzerland

Correspondence: Address reprint requests to R. Weingart, Dept. of Physiology, University of Bern, Bühlplatz 5, CH-3012, Bern, Switzerland. Tel.: 41-031-631-8706; Fax: 41-031-631-4611; E-mail: weingart{at}pyl.unibe.ch.

Human HeLa cells expressing mouse connexin30 were used to study the electrical properties of gap junction channel substates. Experiments were performed on cell pairs using a dual voltage-clamp method. Single-channel currents revealed discrete levels attributable to a main state, a residual state, and five substates interposed, suggesting the operation of six subgates provided by the six connexins of a gap junction hemichannel. Substate conductances, _j,substate, were unevenly distributed between the main-state and the residual-state conductance (_{j,main state} = 141 pS, _{j,residual state} = 21 pS). Activation of the first subgate reduced the channel conductance by 30%, and activation of subsequent subgates resulted in conductance decrements of 10–15% each. Current transitions between the states were fast (<2 ms). Substate events were usually demarcated by transitions from and back to the main state; transitions among substates were rare. Hence, subgates are recruited simultaneously rather than sequentially. The incidence of substate events was larger at larger gradients of V_j. Frequency and duration of substate events increased with increasing number of synchronously activated subgates. Our mathematical model, which describes the operation of gap junction channels, was expanded to include channel substates. Based on the established V_j-sensitivity of _{j,main state} and _{j,residual state}, the simulation yielded unique functions _j,substate = f(V_j) for each substate. Hence, the spacing of subconductance levels between the channel main state and residual state were uneven and characteristic for each V_j.