Temperature Dependence of Voltage-gated H(+) Currents in Human Neutrophils, Rat Alveolar Epithelial Cells, and Mammalian Phagocytes

H(+) currents in human neutrophils, rat alveolar epithelial cells, and several mammalian phagocyte cell lines were studied using whole-cell and excised-patch tight-seal voltage clamp techniques at temperatures between 6 and 42°C. Effects of temperature on gating kinetics were distinguished from effects on the H(+) current amplitude. The activation and deactivation of H(+) currents were both highly temperature sensitive, with a Q (10 )of 6–9 (activation energy, E (a), ≈ 30–38 kcal/mol), greater than for most other ion channels. The similarity of E (a) for channel opening and closing suggests that the same step may be rate determining. In addition, when the turn-on of H(+) currents with depolarization was fitted by a delay and single exponential, both the delay and the time constant (τ(act)) had similarly high Q (10). These results could be explained if H(+) channels were composed of several subunits, each of which undergoes a single rate-determining gating transition. H(+) current gating in all mammalian cells studied had similarly strong temperature dependences. The H(+) conductance increased markedly with temperature, with Q (10) ≥ 2 in whole-cell experiments. In excised patches where depletion would affect the measurement less, the Q (10) was 2.8 at >20°C and 5.3 at <20°C. This temperature sensitivity is much greater than for most other ion channels and for H(+) conduction in aqueous solution, but is in the range reported for H(+) transport mechanisms other than channels; e.g., carriers and pumps. Evidently, under the conditions employed, the rate-determining step in H(+) permeation occurs not in the diffusional approach but during permeation through the channel itself. The large E (a) of permeation intrinsically limits the conductance of this channel, and appears inconsistent with the channel being a water-filled pore. At physiological temperature, H(+) channels provide mammalian cells with an enormous capacity for proton extrusion.