The rectification of heterotypic Cx46/Cx50 gap junction channels depends on intracellular magnesium.

Gap junction (GJ) intercellular communication is crucial in many physiological and pathological processes. A GJ channel is formed by head-to-head docking of two hexameric hemichannels from two neighboring cells. Heterotypic GJ channels formed by two different homomeric connexin hemichannels often display rectification properties in the current-voltage relationship while the underlying mechanisms are not fully clear. Here we studied heterotypic Cx46/Cx50 GJs at a single GJ channel level. Our data showed unitary Cx46/Cx50 GJ channel conductance (γ) rectification when 5 mmol/L Mg was included in the patch pipette solution, while no γ rectification was observed when no Mg was added. Including 5 mmol/L Mg in pipette solution significantly decreased the γ of homotypic Cx46 GJ with little change in homotypic Cx50 γ. A missense point variant in Cx46 (E43F) reduced the Mg-dependent reduction in γ of Cx46 E43F GJ, indicating that E43 might be partially responsible for Mg-dependent decrease in γ of Cx46. A comprehensive understanding of Mg modulation of GJ at the individual channel level is useful in understanding factors in modulating GJ-mediated intercellular communication in health and diseases.