Tonic and phasic guanidinium toxin-block of skeletal muscle Na channels expressed in Mammalian cells.

TitleTonic and phasic guanidinium toxin-block of skeletal muscle Na channels expressed in Mammalian cells.
Publication TypeJournal Article
Year of Publication2003
AuthorsMoran O, Picollo A, Conti F
JournalBiophys J
Date Published2003 May
KeywordsAdaptation, Physiological, Animals, CHO Cells, Computer Simulation, Cricetinae, Cricetulus, Dose-Response Relationship, Drug, Guanidine, Ion Channel Gating, Mammals, Membrane Potentials, Models, Biological, Muscle Proteins, Muscle, Skeletal, NAV1.4 Voltage-Gated Sodium Channel, Porosity, Rats, Recombinant Proteins, Saxitoxin, Sodium Channels, Tetrodotoxin

The blockage of skeletal muscle sodium channels by tetrodotoxin (TTX) and saxitoxin (STX) have been studied in CHO cells permanently expressing rat Nav1.4 channels. Tonic and use-dependent blockage were analyzed in the framework of the ion-trapped model. The tonic affinity (26.6 nM) and the maximum affinity (7.7 nM) of TTX, as well as the "on" and "off" rate constants measured in this preparation, are in remarkably good agreement with those measured for Nav1.2 expressed in frog oocytes, indicating that the structure of the toxin receptor of Nav1.4 and Nav1.2 channels are very similar and that the expression method does not have any influence on the pore properties of the sodium channel. The higher affinity of STX for the sodium channels (tonic and maximum affinity of 1.8 nM and 0.74 nM respectively) is explained as an increase on the "on" rate constant (approximately 0.03 s(-1) nM(-1)), compared to that of TTX (approximately 0.003 s(-1) nM(-1)), while the "off" rate constant is the same for both toxins (approximately 0.02 s(-1)). Estimations of the free-energy differences of the toxin-channel interaction indicate that STX is bound in a more external position than TTX. Similarly, the comparison of the toxins free energy of binding to a ion-free, Na(+)- and Ca(2+)-occupied channel, is consistent with a binding site in the selectivity filter for Ca(2+) more external than for Na(+). This data may be useful in further attempts at sodium-channel pore modeling.

Alternate JournalBiophys. J.
PubMed ID12719231
PubMed Central IDPMC1302862