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Characterization of the palytoxin‐induced sodium conductance in frog skeletal muscle
Author(s) -
Ecault Eudes,
Sauviat MartinPierre
Publication year - 1991
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1991.tb12204.x
Subject(s) - palytoxin , tetrodotoxin , biophysics , chemistry , depolarization , voltage clamp , divalent , skeletal muscle , amiloride , membrane potential , conductance , resting potential , sodium , ouabain , biochemistry , anatomy , biology , toxin , mathematics , organic chemistry , combinatorics
1 The effects of palytoxin (PTX) on transmembrane potentials and currents of frog skeletal muscle were analyzed by intracellular microelectrode techniques and the double sucrose‐gap voltage clamp method. 2 PTX irreversibly depolarized the membrane. The depolarization was Na‐sensitive. 3 Under voltage clamp, PTX induced an inward resting current which did not inactivate, was inhibited by external Na + removal and was a function of external Na concentration. 4 This resting current could be carried either by Na + , Li + , K + or by guanidinium according to the permeability sequence K + < Li + < Na + < Gua + . 5 The PTX‐induced current was only weakly sensitive to tetrodotoxin. It was reversibly and dose‐dependently inhibited by amiloride with a one to one stoichiometry and a K D of 0.3 m m . 6 Acidic pH partially inhibited the current induced by PTX which was also highly sensitive to external Cd 2+ and La 3+ . The inhibitory sequence for divalent cations was: Mg 2+ < Ca 2+ = Ba 2+ = Mn 2+ < Cd 2+ ; with La 3+ > Cd 2+ . 7 The amplitude of the PTX‐induced I rest was markedly reduced in the absence of external Ca 2+ . 8 PTX induced a Na + resting conductance in frog skeletal muscle. The size of the channel induced by PTX is larger than the guanidinium ion. External membrane Ca 2+ might be a cofactor involved in the mode of action of PTX.