Decreased rate of sodium conductance inactivation in the node of Ranvier induced by a polypeptide toxin from sea anemone
| Autor: | E Rojas, J.M. Dubois, W. Rathmayer, Claude Bergman |
|---|---|
| Rok vydání: | 1976 |
| Předmět: |
Stereochemistry
Sodium Potassium Biophysics chemistry.chemical_element Gating medicine.disease_cause Biochemistry Rana Reaction rate constant Ranvier's Nodes medicine Animals Toxin Electric Conductivity Rana esculenta Conductance Biological Transport Cell Biology Dissociation constant Kinetics Sea Anemones chemistry Marine Toxins Peptides Mathematics |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Biomembranes. 455:173-184 |
| ISSN: | 0005-2736 |
| DOI: | 10.1016/0005-2736(76)90162-0 |
| Popis: | The effects of two toxins extracted from the tentacles of Anemonia sulcata on ionic currents have been tested on the nodal membrane of myelinated nerve fibres from Rana esculenta. While external application of Toxin I at 100 muM leaves both specific ionic currents unmodified, Toxin II at 10 muM reacts with a receptor site associated with the sodium conductance inactivation gating. Since internal application by diffusion of Toxin II at a concentration of 700 muM leaves the ionic currents unchanged, the receptor site is most likely located on the external side of the nodal membrane. An equilibrium dissociation constant for the effects of Toxin II was estimated as 20 muM. The on-reaction is fast (rate constant for the on-reaction roughly equal to 3.103 M-1) suggesting a readily accesible receptor site for the toxin. The kinetics characteristics of the sodium currents recorded in the presence of Toxin II suggest that there are at least two steps in the reaction leading to Na+ -channels with the inactivation gate completely immobilized. The relatively fast reversibility of the intermediate stage of the reaction and the rather slow but, in the end, complete reversal of the toxin effects suggest that the toxin acts by modifying the energy profile for the transition "inactivation gate in the open configuration to inactivation gate in the closed configuration." Toxin II at higher concentrations (greater than 100 muM) also inhibits the potassium currents but these effects were not studied in any detail. |
| Databáze: | OpenAIRE |
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