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.