The effect of temperature on the asymmetrical charge movement in squid giant axons.

Abstract

Asymmetrical displacement currents (gating currents) were recorded in intracellularly perfused squid [Loligo forbesi and L. vulgaris] giant axons by averaging the currents associated with depolarizing and hyperpolarizing voltage pulses. The effect of temperature on gating currents was studied and compared with the effect of temperature on Na currents. Increasing the temperature in 7 steps from 0-15.degree. C increased the area under the on- and off-response (Qon, Qoff). The average Q10 values for Qon and Qoff (measured with depolarizing pulses to 0 or 20 mV) were 1.41 and 1.62, respectively. The on- and off-responses were described mathematically by the sum of 2 exponentials. The 1st component of the on-response, Qon 1, represented 80% or more of the total charge movement associated with 2.5 ms pulses; the Q10 of Qon 1 was similar to that of total Qon. The 1st component of the off-response, Qoff 1, represented 50-70% of total Qoff; its Q10 was smaller than that of total Qoff. The temperature dependence of the rate constants (.tau.on 1)-1 and (.tau.off 1)-1 was stronger at temperatures below 6-8.degree. C (Q10 = 3.1-6.4) than at higher temperatures (Q10 = 2.0-3.3). In an Arrhenius plot 2 lines of different slope were required to fit the data. The effect of increasing the temperature on the Q [response] vs. V [voltage] curve can be described as an increase of Qmax or, alternatively, as a shift of the curve to more negative potentials. Increasing the temperature from 0-15.degree. C increased the peak of the Na current (recorded in seawater with 1/5 of the normal Na concentration), increased the rate constants, .tau.m-1 and .tau.h-1, and shifted the .**GRAPHIC**. and h.infin. curves to more positive potentials. The Q10 of the rate constant .tau.m-1 varied between 2.04-2.61 and was independent of temperature. In an Arrhenius plot the values for .tau.m-1 could be fitted by a single line. Gating current does not simply reflect changes of the Na activation variable m. The increase of Qon, Qoff with increasing temperature may be attributed to an increase in membrane fluidity. The possibility that those charges which become mobile at higher temperatures may not be related to gating is considered.