Effects of temperature on transjunctional voltage-dependent gating kinetics in Cx45 and Cx40 gap junction channels.

Gap junctions (GJs) are intercellular channels directly linking neighbouring cells and are dodecamers of connexins. In the human heart, connexin40 (Cx40), Cx43, and Cx45 are expressed in different regions of the heart forming GJs ensuring rapid propagation of action potentials in the myocardium. Two of these connexins, Cx40 and Cx45, formed functional GJs with prominent transjunctional voltage-dependent gating (V_j-gating), which can be a mechanism to down regulate coupling conductance (G_j). It is not clear the effects of temperature on V_j-gating properties. We expressed Cx40 or Cx45 in N2A cells to study the V_j-gating extent, the kinetics of deactivation, and the recovery time course from deactivation at 22 °C, 28 °C, and 32 °C. Dynamic uncoupling between cell pairs were evaluated at different temperatures, junctional delays, and/or repeating frequencies. Cx40 or Cx45 GJs showed little changes in the extent of V_j-gating, but in both cases with a faster deactivation kinetics at high temperatures. The recovery from deactivation was faster at higher temperatures for Cx45 GJs, but not for Cx40 GJs. Cx45 GJs, but not Cx40 GJs, were dynamically uncoupled when sufficient junctional delays and/or repeating frequency in all tested temperatures. Gap junction specific dynamic uncoupling could play an important role in regulating action potential propagation speed in Cx45 enriched nodal cells in the heart.

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