抄録
The conductance of voltage-gated proton channels (Hv channels) has a strong temperature dependence (Q10 ≥2), which is distinct from other water-filled pore channels. The temperature dependence of Hv channels in rat microglia (brain phagocyte) was evaluated over a wide range of temperatures (15–45°C) under various cellular conditions. The gating time constants exhibited a monotonic response, with high values of Q10 (4–6), but the temperature dependence of the conductance showed a breakpoint at the transition temperature ( Ttrans ). The Q10 below Ttrans was about ∼2.5 (the high Q10 phase) and above Ttrans it was about ∼1.3 (the low Q10 phase). An increase in the pH gradient across the cell membrane shifted Ttrans to lower temperatures, and cell swelling lowered Ttrans further. Moreover, the value of Ttrans fluctuated even in a single cell from ≤ 20°C to ≥ 33°C. Thus, Ttrans is not likely the phase transition temperature of the membrane lipid. We conclude that the two Q10 phases are based on the distinct physical processes: The low Q10 phase represents H+ conductance through the maximal number of the open channels and the high Q10 phase is due to the recruitment of ready-to-activate channels. Under physiological conditions the high Q10 phase predominates, thus, temperature serves as a critical regulatory factor for the Hv channel through the recruitment mechanism. [Jpn J Physiol 55 Suppl:S69 (2005)]
