Ion permeation through single ACh-activated channels in denervated adult toad sartorius skeletal muscle fibres: effect of temperature

Abstract

The gigaohm seal technique was used to study the effects of temperature on ion permeation through acetylcholine-activated channels. This was done in cell-attached patches of the extrajunctional membrane of chronically-denervated, enzyme-treated cells from sartorius muscle of the toad Bufo marinus. The predominant extracellular cation in the pipette solution was Na+. Single channel current-voltage curves were measured at different temperatures and electrodiffusion and three-site-four-barrier rate theory models were used to characterize ion permeation through the channels and determine the effects of temperature on permeation parameters. The fitting of the experimental data to these models suggested the presence of at least three and probably more ion-selective sites within the channel. The most frequently occurring channel type (greater than 95% of channel openings) had a chord conductance of 25 pS at 11 degrees C and -70 mV and was classified as 'extrajunctional'. The single channel conductance of this channel had a low temperature-dependence (Q10 approximately equal to 1.3). The apparent activation enthalpy, Ea, for the conductance between 11 degrees C and 20 degrees C, did not appear to be significantly voltage-sensitive and had a value of about 17 +/- 2 kJ . mol-1 at a voltage of -70 mV. The Arrhenius plot of conductance appeared linear between 11 and 20 degrees C at all potentials examined. The data was consistent with a break in the slope of the Arrhenius plot at temperatures between 5 and 11 degrees C at all potentials examined, suggesting a possible phase transition of the membrane lipids. In contrast to the relative permeability, which was not very temperature sensitive, the relative binding constant was significantly affected by temperature. The relative Na/K binding constant sequence was: K5 degrees C greater than K20 degrees C greater than K15 degrees C much greater than K11 degrees C. In addition, the decrease in conductance observed at the most depolarized potentials was accentuated as the temperature was increased, suggesting a rate-limiting access step for ions from the intracellular solution into the channel.

Changes in Temperature Have Opposing Effects on Current Amplitude in α7 and α4β2 Nicotinic Acetylcholine Receptors

“…Indeed, it has been reported that the conductance of muscle-type nAChRs increases with increasing temperature [36], [37], [38], [39]. As has been discussed previously in connection with the effects of temperature on functional properties of acetylcholine-gated chloride channels from the pond snail Lymnaea [25], alternative possibilities for the effects that we have observed include temperature-dependent changes in single-channel kinetics and/or changes in the affinity of agonist binding.…”

Caveolae Regulation of Mechanosensitive Channel Function in Myotubes

“…S4A and B). The increase corresponds to a Q 10 of 1.6, consistent with the permeation rate increase expected for ion channel pores [50]. We used patch capacitance measurements (ΔCp) to monitor changes in the dome area and parameterized the mechanical relaxation kinetics at both temperatures by curve fitting (Fig.…”

Effects of temperature on silkmoth olfactory responses to pheromone can be simulated by modulation of resting cell membrane resistances

“…For instance, it seems possible, that temperature increase leads to a higher conductance but also to shorter opening times of ion channels which could compensate and, thus, result in a lack of net effect. Generally, ion channel conductivity, gating kinetics and open probability are affected by temperature (Romey et al 1980;Ffrench-Mullen et al 1988;Quartararo and Barry 1988;Krasilnikov and Sabirov 1989).…”