Temperature sensitivity of the tonoplast Ca²⁺-activated K⁺ channel in Chara: The influence of reversing the sign of membrane potential

Abstract

A detailed temperature dependence study of a well-defined plant ion channel, the Ca2+-activated K+ channel of Chara corallina, was performed over the temperature range of their habitats, 5-36°C, at 1°C resolution. The temperature dependence of the channel unitary conductance at 50 mV shows discontinuities at 15 and 30°C. These temperatures limit the range within which ion diffusion is characterized by the lowest activation energy (E(a) = 8.0 ± 1.6 kJ/mol) as compared to the regions below 15°C and above 30°C. Upon reversing membrane voltage polarity from 50 to -50 mV the pattern of temperature dependence switched from discontinuous to linear with E(a) = 13.6 ± 0.5 kJ/mol. The temperature dependence of the effective number of open channels at 50 mV showed a decrease with increasing temperature, with a local minimum at 28°C. The mean open time exhibited a similar behavior. Changing the sign of membrane potential from 50 to -50 mV abolished the minima in both temperature dependencies. These data are discussed in the light of higher order phase transitions of the Characean membrane lipids and corresponding change in the lipid-protein interaction, and their modulation by transmembrane voltage.