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, gj, and temperature. Cooling from 37° C to 14° C led to a steeper decrease in gj, cooling from 14° C to -2° C to a shallower decrease (37° C: gj=48.3 nS; 14° C: gj=21.4 nS;-2°C: gj=17.5 nS), corresponding to a temperature coefficient, Q10, of 1.43 and 1.14 respectively. The existence of two Q10 values implies that gj may be controlled by enzymatic reactions. When gj 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 gj 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, γj, and temperature (37° C: 75.6 pS; -2°C: 19.6 pS), corresponding to a Q10 of 1.41.
Neonatal rat heart Cardiac cells Gap junctions Electrical coupling Temperature