RT Journal Article
SR Electronic
T1 Block of single batrachotoxin-activated Na+ channels by clofilium.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 352
OP 358
VO 39
IS 3
A1 J Nettleton
A1 N A Castle
A1 G K Wang
YR 1991
UL http://molpharm.aspetjournals.org/content/39/3/352.abstract
AB The effects of clofilium on single batrachotoxin-activated Na+ channels from rabbit skeletal muscle, incorporated into planar bilayers, were studied under symmetrical 200 mM NaCl conditions. Internally applied clofilium (0.3-30 microM) induced long lasting closures, with a mean duration of approximately 450 msec at +50 mV. The fraction of time spent in the clofilium-induced closed state was concentration dependent, with an equilibrium dissociation constant (Kd) of 3.4 microM at +50 mV. Kinetic analysis showed that both open and closed time distributions were well described by single exponentials, with respective time constants of tau o and tau C. As expected for an open channel blocker, 1/tau o increased linearly with increasing clofilium concentration, whereas 1/tau c remained relatively constant. Inhibition of batrachotoxin-activated Na+ channels by clofilium exhibited a strong voltage dependence. The binding affinity of clofilium increased about 10-fold upon depolarization from -50 mV to 50 mV. Competition studies using quaternary and tertiary local anesthetics showed that clofilium and local anesthetics probably share a common receptor site located about halfway across the membrane electrical field. Together, our results demonstrate that clofilium is a potent Na+ channel blocker in bilayers and its action is similar to that of other local anesthetics characterized previously.