TEMPERATURE-DEPENDENCE OF UNITARY PROPERTIES OF AN ATP-DEPENDENT POTASSIUM CHANNEL IN CARDIAC MYOCYTES

The temperature dependence of the properties of unitary currents in cu ltured rat ventricular myocytes has been studied. Currents flowing thr ough an ATP-dependent K+ channel were recorded from inside-out patches with the bath temperature varied from 10-degrees to 30-degrees-C. The channel conductance was 56 pS at room temperature (22-degrees-C), and the amplitudes of unitary currents and the channel conductance exhibi ted a relatively weak (Q10) from 1.4 to 1.6) dependence on temperature . The temperature dependence of channel mean open times was biphasic w ith the low temperature (10-20-degrees-C) range showing a relatively s tronger temperature dependence (Q10 of 2.3) than the high temperature (20-30-degrees-C) range (Q10 of 1.6). The activation energies for the two regions were determined from an Arrhenius plot with the activation energy, corresponding to the lower temperature range, near 16 kcal/mo l. Thermodynamic analysis, using transition rate theory, indicated tha t the formation of a transition state prior to channel closure to be a ssociated with a positive entropy component for the high Q10 region.