title: Mg2+ block and inward rectification of mechanosensitive channels in Xenopus oocytes.
abstract: The effects of Mg2+ on single mechanosensitive (MS) channel currents recorded from Xenopus oocytes were studied using cell-attached and inside-out patch configurations. Mg2+ both permeates and blocks MS channels. Under symmetrical ionic conditions, the blocking effects of Mg2+ can be described by a Hill coefficient of 0.9 at +/-100 mV and IC50s of 0.12 mM (-100 mV) and 0.60 mM at (+100 mV). Although block by intracellular Mg2+ may contribute to inward MS channel rectification, significant current rectification is retained even under symmetrical KCl concentrations and in the complete absence of Mg2+. The observed voltage dependencies of the IC50 for Mg2+ block and the Km for K+ current saturation indicate asymmetries in the MS channel pore. In addition, the absence of K+ self block and anomalous mole fraction effects with K+/Tl+ mixtures indicate a single site pore model.
authors.affiliation: Department of Physiology and Biophysics, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555-0641, USA.
authors.forename: G
authors.initials: G
authors.lastname: Wu
authors.forename: D W
authors.initials: DW
authors.lastname: McBride
authors.forename: O P
authors.initials: OP
authors.lastname: Hamill
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008465:Mechanoreceptors / Q000187:drug effects*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011189:Potassium Chloride / Q000494:pharmacology; D014981:Xenopus
chemical_list: D007473:Ion Channels; D011189:Potassium Chloride; D008274:Magnesium