Outward Currents Through “low” Conductance Non-Mechanosensitive Channels in Escherichia Coli Membranes

Abstract

Mechanosensitive high conductance channels in bacteria have received considerable attention (e.g.1,2) and have a presumed role against osmotic stress. In contrast non-mechanosensitive channels are less well described. In patch-clamp on-spheroplast recordings from E. coli (BW25113) with high K+ (200 mM) in both the pipette and bath solution MscL, MscK, MscS and MscM channels are reproducibly seen, and appear to be the only channels present. In on-spheroplast recordings with high Ca2+ or Mg2+ (100 mM) in the pipette and bath solution both MscL and MscM channels are observed. In addition, lower conductance channels of < 30 pS (n = 12) and 80 - 100 pS (n = 12) respectively are observed at depolarised potentials (pipette potential - 55 mV and above) in the absence of applied pressure in these solutions. These openings are long duration, non-flickery (in the case of the < 30 pS channel) and shorter duration, flickery (in the case of the 80-100 pS channel). The I-V relationships appear linear over a limited voltage range (pipette potentials −55 to −90 mV). The “low” conductance channels are seen in the absence of Cl- ions (sulphate as replacement) in the pipette and bath solutions. These channels are not seen in excised inside-out patches (n = 6). The identity, ionic selectivity and role of these channels remain to be characterised. An anion preferring 100 pS conductance channel in the absence of applied pressure has been reported previously in excised patches at both depolarised and hyperpolarised potentials in high K+ (150) solutions (3).1. Martinac, B. et al. PNAS, 84, 2297-2301 (1987)2. Booth, I.R. et al. Nature Rev. Microbiol., 5, 431-440 (2007).3. Kubalski, A. Biochim. et Biophys. Acta, 1238, 177-182 (1995)1CDC is supported by a Cardiff University Endowment Scholarship.