Figure 8.
Kinetics of proton currents generated by the normal dimeric human proton channel, hHV1 (a) and a monomeric construct produced when the C terminus was truncated, hHV1ΔC (b). The dimeric channel, which occurs in native cells [276], opens with sigmoid kinetics and approximately five times slower than monomeric constructs (note different time scales). Conditions are the same, pHi = pHo = 7.5, 23°C, voltage pulses to +50 mV. In (c), the S4 helix of the Ciona intestinalis proton channel was labelled with a fluorescent tag that moves when the channel opens upon depolarization (upper noisy traces), preceding the activation of current (black line). In a Hodgkin–Huxley type cooperative gating mechanism [252], both subunits move before either conducts and the predicted time course is sigmoidal, the square of the motion time course (lower noisy traces, superimposed on line) (a,b adapted from [223]; c from [272]).