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EFFECT OF Gymnodinium breve TOXIN IN THE RAT PHRENIC NERVE DIAPHRAGM PREPARATION
Author(s) -
GALLAGHER JOEL P.,
SHINNICKGALLAGHER PATRICIA
Publication year - 1980
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.1476-5381.1980.tb07023.x
Subject(s) - depolarization , phrenic nerve , membrane potential , biophysics , diaphragm (acoustics) , chemistry , anatomy , compound muscle action potential , neuromuscular junction , toxin , medicine , endocrinology , electrophysiology , biology , biochemistry , respiratory system , neuroscience , physics , acoustics , loudspeaker
1 The effects of a crude fraction of Gymnodinium breve toxin (GBTX) were studied on the rat phrenic nerve diaphragm preparation. 2 Indirectly stimulated muscle contractions were more sensitive to blockade by increasing concentrations of GBTX (0.25 μg/ml to 10 μg/ml) than direct muscle contractions. 3 GBTX increased miniature endplate potential (m.e.p.p.) frequency and depolarized the resting membrane potential of the muscle fibres at the endplate and in non‐synaptic regions of muscle fibre. 4 A concentration‐dependent biphasic effect on m.e.p.p. amplitude was evident. At lower concentrations m.e.p.p. amplitudes were depressed whereas at high concentrations they were increased. 5 GBTX blocked endplate potentials (e.p.ps) in concentrations (0.5 μg/ml to 2 μg/ml) that did not block m.e.p.ps. 6 Muscle fibre action potentials recorded from cells held at control membrane potential by hyperpolarizing current were not altered by toxin treatment. No repetitive e.p.ps, or muscle action potentials were observed. 7 These data suggest that GBTX may block indirectly stimulated muscle contractions and e.p.ps by depolarizing the nerve terminal in a manner similar to the observed depolarization of the muscle fibre. The depolarization of the nerve terminal may be sufficient to inhibit transmitter release.