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 (τact) 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.