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Chemical modification of squid axon K+ channel -SH groups with the organic mercurial compoundp-hydroxymercuriphenylsulfonic acid (PHMPS)

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Abstract

In internally dialyzed voltage-clamped squid axons, intracellular or extracellular addition of the sulfhydryl group (-SH) specific reagentp-hydroxymercuriphenylsulfonic acid (PHMPS), causes major modifications in the magnitude and kinetic parameters of the delayed rectifier K+ current. PHMPS produces a dramatic slow-down of the macroscopic current activation kinetics with a simultaneous reduction in its amplitude. In addition, it causes a marked increase in the delay of the macroscopic current at various pre-pulse potentials (Cole-Moore shift). The main effect of PHMPS at the single channel level is a sharp decrease in the open probability (4- to 5-fold). There is, however, a small reduction in single channel conductance (20%). Gating current experiments indicate that PHMPS causes a reduction in the voltage dependence of the activation process as well as a shift of the charge/voltage relationship towards more positive potentials. This, together with an increase in the mean open time, suggests that the open state has been destabilized. The results indicate that the reaction of -SH groups with PHMPS differentially affects the gating process. All the above mentioned effects are partially reversed by either dithiotreitol orβ-mercaptoethanol,-SH group reducing agents.

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Authors and Affiliations

  1. Centro de Biofisica y Bioquimica, Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela

    Carlo Caputo

  2. Department of Physiology and Jerry Lewis Neuromuscular Center, UCLA, 90024, Los Angeles, CA, USA

    Francisco Bezanilla

  3. Jules Stein Eye Institute and Dept. of Chemistry and Biochemistry, UCLA, 90024, Los Angeles, CA, USA

    Eduardo Perozo

  4. Marine Biological Laboratory, 02543, Woods Hole, MA, USA

    Carlo Caputo, Eduardo Perozo & Francisco Bezanilla

Authors
  1. Carlo Caputo
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  2. Eduardo Perozo
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  3. Francisco Bezanilla
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Caputo, C., Perozo, E. & Bezanilla, F. Chemical modification of squid axon K+ channel -SH groups with the organic mercurial compoundp-hydroxymercuriphenylsulfonic acid (PHMPS). Pflügers Arch. 428, 315–322 (1994). https://doi.org/10.1007/BF00724513

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  • DOI: https://doi.org/10.1007/BF00724513

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