Functional properties of channels formed by the neuronal gap junction protein connexin36

The expression and functional properties of connexin36 (Cx36) were examined in two communication-deficient cell lines (N2A-neuroblastoma and PC-12 cel ls) transfected with Cx36 and in hippocampal neurons that express the conne xin endogenously. Transfected cells expressed the expected 2.9 kb Cx36 tran script and Cx36 immunoreactivity, whereas nontransfected cells were devoid of Cx36. The relationship between steady-state junctional conductance (g(j) ) and transjunctional voltage was well described by a two-state Boltzmann e quation. The half-inactivation voltage (V-0), the ratio of minimal to maxim al g(j) (g(min)/g(max)), and the equivalent gating charge were +/- 75 mV, 0 .55, and 1.75, respectively, indicating that Cx36 exhibits very low voltage sensitivity. Conductance of single Cx36 channels measured with patch pipet tes containing 130 mM CsCl was 10-15 pS (n = 15 cell pairs); despite this l ow unitary conductance, Cx36 channels were permeable to the dye Lucifer yel low. Hippocampal neurons expressed Cx36 both in vivo and in culture. The el ectrophysiological properties of channels in cultured hippocampal neurons w ere similar to those of the channels expressed by the transfected cell line s, and the neuronal channels were similarly permeable to Lucifer yellow. Th e unique combination of weak voltage sensitivity, small unitary conductance , and permeation by anions as large as second messenger molecules endows Cx 36 gap junction channels with properties well suited for mediating flexible electrical and biochemical interactions between neurons.