MULTIPLE MECHANOSENSITIVE ION CHANNELS FROM ESCHERICHIA-COLI, ACTIVATED AT DIFFERENT THRESHOLDS OF APPLIED PRESSURE

Mechanosensitive ion channels from Escherichia coli were studied in gi ant proteoliposomes reconstituted from an inner membrane fraction, or in giant round cells in which the outer membrane and the cell wall had been disrupted by a lysozyme-EDTA treatment and a mild osmotic shock. Patch-clamp experiments revealed the presence in these two preparatio ns of an array of different conductances (100 to 2,300 pS in 0.1 M KCl ) activated by stretch. The electrical activity induced by stretch in the native membrane was complex, due to the activation of several diff erent conductances. In contrast, patches of proteoliposomes generally contained clusters of identical conductances, which differed from patc h to patch. These experiments are consistent with the notion that thes e different conductances correspond to different proteins in the plasm a membrane of E. coli, which segregate into clusters of identical chan nels on dilution involved in reconstitution in proteoliposomes. These conductances could be grouped into three subfamilies of poorly selecti ve channels. In both preparations, the higher the conductance, the hig her was the negative pressure needed for activation. We discuss the pu tative role of these channels as parts of a multicomponent osmo-regula tory system.