Influence of Na+and Li+ions on the kinetics of sodium channel block by tetrodotoxin and saxitoxin

✍ Scribed by G. Hansen; W. Ulbricht

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 826 KB
• Volume: 419
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00370300

✦ Synopsis

Voltage clamp experiments were done on single myelinated frog nerve fibres. The rate of block of Na + channels by tetrodotoxin (TTX) was obtained from changes in peak Na + current during 1-Hz trains of depolarizing impulses. In hypertonic Na+-rich solution (216 raM) the stationary block was reduced compared with Na+-poor solutions (54raM or less; tetramethylammonium ions substituting for Na+). Washout in 216 mM Na + was faster than in 54 mM Na +. Concentration of Na + ([Na+]) little affected onset of block. After equilibration in Na+-poor TTX solution, a sudden application of Na+-rich toxin solution led to a partial relief from block that proceeded faster than the onset in the latter solution. Comparable results were obtained with saxitoxin (STX) and in analogous Li + solutions. Most of the observed phenomena could be quantitatively fitted by a cyclic model in which cations favour the transition of channels (unblocked and blocked) from a highto a low-affinity state from which toxin dissociates faster.