Temperature dependence of gap junction properties in neonatal rat heart cells

Cell pairs of neonatal rat hearts were used to study the influence of temperature on the electrical properties of gap junctions. A dual voltage-clamp method was adopted, which allowed the voltage gradient between the cells to be controlled and the intercellular current flow to be measured. Cell pairs with normal coupling revealed a positive correlation between the conductance of the junctional membranes, g_j, and temperature. Cooling from 37° C to 14° C led to a steeper decrease in g_j, cooling from 14° C to -2° C to a shallower decrease (37° C: g_j=48.3 nS; 14° C: g_j=21.4 nS;-2°C: g_j=17.5 nS), corresponding to a temperature coefficient, Q₁₀, of 1.43 and 1.14 respectively. The existence of two Q₁₀ values implies that g_j may be controlled by enzymatic reactions. When g_j was low, i. e. below 5 nS (conditions: low temperature; treatment with 3 mM heptanol), it showed voltage-dependent gating. This property was not visible when g_j was large, i. e. 20-70 nS (conditions: high temperature; normal saline), presumably because of series resistances (pipette resistance). Cell pairs with weak intrinsic coupling and normally coupled cell pairs treated with 3 mM heptanol revealed a positive correlation between the conductance of single gap-junction channels, γ_j, and temperature (37° C: 75.6 pS; -2°C: 19.6 pS), corresponding to a Q₁₀ of 1.41.