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Effect of palytoxin on the calcium current and the mechanical activity of frog heart muscle
Author(s) -
Sauviat MartinPierre
Publication year - 1989
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.1476-5381.1989.tb14605.x
Subject(s) - palytoxin , biophysics , chemistry , calcium , membrane potential , sucrose gap , voltage clamp , endocrinology , medicine , biochemistry , biology , toxin , organic chemistry
1 The effect of palytoxin (PTX) on the Ca current (I Ca ) and the mechanical activity of frog atrial fibres was studied by use of the double sucrose gap voltage clamp technique. 2 In normal Ringer solution, PTX transiently increased the electrically‐evoked peak tension which then decreased while a major contracture developed. PTX slowed the time course of the relaxation phase of the evoked tension. 3 Evidence is presented which suggests that the toxin also increased the entry of Ca and Sr via the Na‐Ca exchange mechanism. It also induced the development of a Ca‐dependent outward current which was inhibited by Sr. 4 In Na‐free solution, PTX increased I Ca and shifted the reversal potential for Ca towards more negative membrane potentials, thus suggesting that the internal Ca concentration had increased. Current‐voltage, tension‐voltage, time to peak‐voltage and inactivation time constant‐membrane potential curves were all shifted towards more negative membrane potentials in the presence of PTX. 5 These effects of PTX are similar to those caused by the increase in internal Ca concentration induced by Na ionophores by way of voltage‐dependent Ca influx of the Na‐Ca exchange mechanism.