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-degrees-C to 14-degrees-C led to a steeper decrease in g(j), cooling from 14-degrees-C to -2-degrees-C to a shallower decrease (37-degrees-C: g(j) = 48.3 nS; 14-degrees-C: g(j) = 21.4 nS; -2-degrees-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, gamma(j), and temperature (37-degrees-C: 75.6 pS; -2-degrees-C: 19.6 pS), corresponding to a Q10 of 1.41.