Desensitization of mechano-gated K 2P channels

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Abstract
The neuronal mechano-gated K2P channels TREK-1 and TRAAK show pronounced desensitization within 100 ms of membrane stretch. Desensitization persists in the presence of cytoskeleton disrupting agents, upon patch excision, and when channels are expressed in membrane blebs. Mechanosensitive currents evoked with a variety of complex stimulus protocols were globally fit to a four-state cyclic kinetic model in detailed balance, without the need to introduce adaptation of the stimulus. However, we show that patch stress can be a complex function of time and stimulation history. The kinetic model couples desensitization to activation, so that gentle conditioning stimuli do not cause desensitization. Prestressing the channels with pressure, amphipaths, intracellular acidosis, or the E306A mutation reduces the peak-to-steady-state ratio by changing the preexponential terms of the rate constants, increasing the steady-state current amplitude. The mechanical responsivity can be accounted for by a change of in-plane area of approximately 2 nm2 between the closed and open conformations. Desensitization and its regulation by chemical messengers is predicted to condition the physiological role of K2P channels.