Premium
An octopus toxin, maculotoxin, selectively blocks sodium current in squid axons.
Author(s) -
Gage P W,
Moore J W,
Westerfield M
Publication year - 1976
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1976.sp011474
Subject(s) - depolarization , sodium , sodium channel , chemistry , neurotoxin , biophysics , squid , toxin , potency , conductance , gating , pharmacology , biochemistry , biology , ecology , mathematics , organic chemistry , combinatorics , in vitro
1. A low molecular weight, stable, cationic neurotoxin (maculotoxin, MTX) extracted from the posterior salivary glands of the octopus Hapalochlaena maculosa, blocked sodium current in voltage‐clamped squid axons without affecting potassium current. 2. The effectiveness of MTX was increased by repetitive, brief, depolarizing pulses but not by a single prolonged depolarization. 3. The potency of MTX decreased at pHs from 8 to 9. Effectiveness could be restored be restored by lowering the pH to 7‐1 again. It was concluded that MTX is active in its cationic form. 4. MTX affected sodium conductance kinetics, slowing the turn‐on of sodium current. This effect was most noticeable with small deploarizations but became progressively less with larger depolarizations. Neither the turn‐off of sodium current nor sodium inactivation kinetics were affected by the toxin. 5. MTX inhibited sodium current without inhibiting sodium gating current. 6. The effectiveness of MTX was not detectably changed when calcium concentration was varied from 50 to 10 mM, or sodium concentration was varied from 225 to 750 mM.