VOLTAGE-INDEPENDENT ADAPTATION OF MECHANOSENSITIVE CHANNELS IN ESCHERICHIA-COLI PROTOPLASTS

Mechanosensitive (MS) ion channels, with 560 pS conductance, opened tr ansiently by rapid application of suction pulses to patches of E. coli protoplast membrane. The adaptation phase of the response was voltage -independent. Application of strong suction pulses, which were suffici ent to cause saturation of the MS current, did not abolish the adaptat ion. Multiple pulse experimental protocols revealed that once MS chann els had fully adapted, they could be reactivated by a second suction p ulse of similar amplitude, providing the time between pulses was long enough and suction had been released between pulses. Limited proteolys is (0.2 mg/ml pronase applied to the cytoplasmic side of the membrane patch) reduced the number of open channels without affecting the adapt ation. Exposing patches to higher levels of pronase (1 mg/ml) removed responsiveness of the channel to suction and abolished adaptation cons istent with disruption of the tension transmission mechanism responsib le for activating the MS channel. Based on these data we discuss a mec hanism for mechanosensitivity mediated by a cytoplasmic domain of the MS channel molecule or associated protein.