Temperature Sencitivity of the K^+ Channel of Chara. A Thermodynamic Analysis : MEMBRANES AND BIOENERGETICS

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Temperature sensitivity of the K^+ channel of Chara cytoplasmic droplets has been characterized by means of the patch-clamp technique. The activity of the channel was recorded in inside-out patches over a range of temperatures (3℃ to 25℃). An increment in the unitary channel conductance and a decrease in the probability of channel opening was found as temperature augmented. This could be explained by the combined effect of a reduction in the mean open duration and an increase in the closed times (Q_<10> values of 0.7 and 1.1-1.6 respectively). Eyring's transition state theory was applied to the thermodynamic analysis of conductance and kinetics of the K^+ channel. The values obtained for the activation enthalpy and entropy were compared with, and found to be similar to, those reported for voltage-dependent K^+ channels in animal cells. The relative insensitivity of channel conductance to temperature (activation enthalpy of 2.4 kcal mol^<-1>) suggests that ions traverse the pore by diffusion. Channel closure appears to have the highest energetic requirements (activation enthalpy of 6.4 kcal mol^<-1>). The channel closing rate, a, exhibits a less negative entropic change (-22.54 cal K^<-1> mol^<-1>), which would provide the driving force for stabilizing the closed configuration of the channel as the temperature increases.
日本植物生理学会の論文