The Journal of General Physiology, Vol 80, 713-731, Copyright © 1982 by The Rockefeller University Press
Modified kinetics and selectivity of sodium channels in frog skeletal muscle fibers treated with aconitine
DT Campbell
The effect of the plant alkaloid aconitine on sodium channel kinetics,
ionic selectivity, and blockage by protons and tetrodotoxin (TTX) has been
studied in frog skeletal muscle. Treatment with 0.25 or 0.3 mM aconitine
alters sodium channels so that the threshold of activation is shifted 40-50
mV in the hyperpolarized direction. In contrast to previous results in frog
nerve, inactivation is complete for depolarizations beyond about -60 mV.
After aconitine treatment, the steady state level of inactivation is
shifted approximately 20 mV in the hyperpolarizing direction. Concomitant
with changes in channel kinetics, the relative permeability of the sodium
channel to NH4,K, and Cs is increased. This altered selectivity is not
accompanied by altered block by protons or TTX. The results suggest that
sites other than those involved in channel block by protons and TTX are
important in determining sodium channel selectivity.