Tityustoxin effect on nerve compound action potentials requires extracellular sodium

Previous studies have demonstrated that Li+ ions can substitute for Na+ in a variety of functional systems. Using the single sucrose-gap recording tec hnique, we measured the nerve compound action potential to study the effect s of tityustoxin (an alpha-scorpion toxin that selectively inhibits fast Na + channel inactivation) upon removal of extracellular Na+. Our results sugg est that tityustoxin requires the presence of extracellular Na+ to produce its typical pharmacological effect on Na+ channel inactivation kinetics, bu t not to bind to its site. (C) 2000 Elsevier Science Ireland Ltd. All right s reserved.