Temperature dependence of the inward rectifier K+ channel gating in guinea-pig ventricular cells

Whole-cell and single-channel currents of the inward rectifier K+ channels from guinea-pig ventricular myocytes were recorded over the range between 5 and 37 degrees C. The conductance for inward currents was decreased by lowering the temperature with a Q10 of 1.28 (whole cell), or 1.41 (single channel) between 20 and 30 degrees C. The open probability of the channel at -100 mV remained high (> 0.9). The distribution of open times was single exponential at all temperatures, confirming a single open state. The entropy change (delta S) for the closing rate of the channel obtained from open-time distribution was -14.0 e.u. (cal/mol/K), and enthalpy change (delta H) was 11.9 kcal/mol. The configuration of closed-time distribution varied markedly by altering the temperature, and three exponentials were necessary to fit the histogram. The slowest component showed higher temperature dependency (delta S = 13.6 e.u. and delta H = 19.0 kcal/mol) than the other two faster components. By assuming a reduced model of C-O at 37 degrees C, the difference in Gibb's free energy (GOC) between the open and closed states was approximately 2 kcal/mol, and the height of the energy barrier for the C-O transition was estimated to be approximately 15 kcal/mol.