Protein mechanosensitive channels (MS) are activated by tension transmittedthrough the lipid bilayer. We propose a theory of lateral stress relaxation ina bilayer lipid membrane exposed to external pressure pulse in the patch-clampexperimental setting. It is shown that transfer of lipid molecules into astrained region is thermodynamically advantageous due to local decrease of thestress. Considered stress relaxation mechanism may explain recent experimentalobservations (Davidson and Martinac 2003) of adaptation of MscL, bacterialmechanosensitive channel of large conductance, to sustained membrane stretch.Lateral stress relaxation in the monolayer, which controls the gating of MscL,triggers thermally activated transition of the open channels back to the closedstate ("adaptation"). We evaluate the contribution of the hydrophobic mismatchbetween MS channel and lipid bilayer to the energy barrier separating open andclosed states. Then, using the MscL thermodynamic model (Sukharev et. al,1999), we estimate characteristic adaptation times at room temperature to be ofthe order of seconds, well in the range of the experimental data (Davidson andMartinac 2003). Estimated propagation time of the initial channel-openingstress over the whole membrane is 4-5 orders of magnitude shorter.
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