CONNEXIN43 GAP-JUNCTIONS EXHIBIT ASYMMETRICAL GATING PROPERTIES

A communication-deficient cell line (RIN cells, derived from a rat isl et tumour), stably transfected with cDNA coding for rat connexin43 (Cx 43), was chosen to further assess the mechanism of voltage gating of C x43 gap junction channels. The experiments were carried out on preform ed cell pairs using a dual whole-cell, voltage-clamp method. The junct ional current, I-j, revealed a time- and voltage-dependent inactivatio n at transjunctional voltages V-j > +/- 40mV. When an asymmetrical pul se protocol was used (in cell 1 the holding potential was maintained, in cell 2 it was altered to establish a Variable V-j), the channels ex hibited an asymmetrical gating behaviour: V-j,V-o = -73.7 mV and 65.1 mV for negative and positive V-j, respectively (V-j at which I-j is ha lf-maximally inactivated); g(j) (min) = 0.34 and 0.29 (normalized mini mal conductance); tau = 350 ms and 80 ms at V-j = 100 mV (time constan t of I-j inactivation). Hence, these parameters were more sensitive to positive V-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), the V-j-dependent asymmetries were absent: I-j,I-0 = -60.5 and 59.5; g(j) (min) = 0.27 and 0.29; tau = 64 ms and 47 ms at 100 mV. Putative explanations for t hese observations are discussed. A possibility is that the number of c hannels alters with the polarity of V-j.