Properties of gap junction channels formed by Cx46 alone and in combination with Cx50

Gap junctions formed of connexin46 (Cx46) and connexin50 (Cx50) in lens fib er cells are crucial for maintaining lens transparency. We determined the f unctional properties of homotypic Cx46, heterotypic Cx46/Cx50, and heterome ric Cx46/Cx50 channels in a communication-deficient neuroblastoma (N2A) cel l line, using dual whole-cell recordings. N2A cultures were stably and/or t ransiently transfected with Cx46, Cx50, and green fluorescent protein (EGFP ). The macroscopic voltage sensitivity of homotypic Cx46 conformed to the t wo-state model (Boltzmann parameters: G(min) = 0.11, V-o = +/- 48.1 mV, gat ing charge = 2). Cx46 single channels showed a main-state conductance of 14 0 +/- 8 pS and multiple subconductance states ranging from less than or equ al to 10 pS to 60 pS. Conservation of homotypic properties in heterotypic C x46/Cx50 cell pairs allowed the determination of a positive relative gating polarity for the dominant gating mechanisms in Cx46 and Cx50. Observed gat ing properties were consistent with a second gating mechanism in Cx46 conne xons. Moreover, rectification was observed in heterotypic cell pairs. Some cell pairs in cultures simultaneously transfected with Cx46 and Cx50 exhibi ted junctional properties not observed in other preparations, suggesting th e formation of heteromeric channels. We conclude that different combination s of Cx46 and Cx50 within gap junction channels lead to unique biophysical properties.