A rapid temperature-pulse method revealed low energy barrier for permeation through the voltage-gated proton channel in microglia

Abstract

Voltage-gated proton (H⁺) channels are expressed in many types of cells and considered to play a pivotal role in compensating for pH imbalances across the plasma membrane. Proton channels are characterized by extremely high selectivity for H⁺ and large H⁺ effluxes. The activity of the channels is highly sensitive to temperature, but the temperature-dependence of the open channel conductance has not been determined. We measured the Q₁₀ value of the permeation process using whole-cell recordings of the proton channel in microglia. We developed a rapid temperature-pulse method which could alter ambient temperature within a few ms: the number of open channels should not change during the period. Relationship between the current ratio immediately before and after a temperature-jump and the amount of changes in temperature (dT: -15–+15°C) gave the Q₁₀ value of 1.5 at 25°C. The activation energy (36.9 kJ/mol) for proton permeation was similar to that for other ion channels with water-filled pore. The Q₁₀ value was not affected by potentials and pH gradients across the membrane, the current magnitude or droop (depletion of protonated buffers by H⁺ extrusion). The Q₁₀ value monotonously decreased by increasing temperature from 4 to 49°C. These data suggest that the permeation mechanism of the proton channel has a unique thermodynamic feature. [J Physiol Sci. 2008;58 Suppl:S79]