Connexin43 gap junctions exhibit asymmetrical gating properties

Abstract

A communication-deficient cell line (RIN cells, derived from a rat islet tumour), stably transfected with cDNA coding for rat connexin43 (Cx43), was chosen to further assess the mechanism of voltage gating of Cx43 gap junction channels. The experiments were carried out on preformed cell pairs using a dual whole-cell, voltage-clamp method. The junctional current,I _j, revealed a time- and voltage-dependent inactivation at transjunctional voltagesV _j > ± 40mV When an asymmetrical pulse protocol was used (in cell 1 the holding potential was maintained, in cell 2 it was altered to establish a variableV _j), the channels exhibited an asymmetrical gating behaviour:V _j,O = −73.7 mV and 65.1 mV for negative and positiveV _j, respectively (V _j at whichI _j is half-maximally inactivated); g_j(min) = 0.34 and 0.29 (normalized minimal conductance); τ = 350 ms and 80 ms atV _j = 100 mV (time constant ofI _j inactivation). Hence, these parameters were more sensitive to positiveV _j values. When a symmetrical pulse protocol was used (the holding potentials in cell 1 and cell 2 were altered simultaneously in steps of equal amplitude but of opposite polarity), theV _j —dependent asymmetries were absent:V _j,O = −60.5 and 59.5; g_j (min) = 0.27 and 0.29; τ = 64 ms and 47 ms at 100 mV Putative explanations for these obervations are discussed. A possibility is that the number of channels alters with the polarity ofV _j.