Block of single batrachotoxin-activated Na+ channels by clofilium.
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.
Nettleton
J
J
Department of Anesthesia Research Laboratories, Harvard Medical School, Boston, Massachusetts.
Castle
N A
NA
Wang
G K
GK
D000818:Animals; D001496:Batrachotoxins / Q000494:pharmacology; D001665:Binding Sites; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008051:Lipid Bilayers; D008564:Membrane Potentials; D009132:Muscles / Q000378:metabolism; D011485:Protein Binding; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D012995:Solubility; D013329:Structure-Activity Relationship
D001496:Batrachotoxins; D008051:Lipid Bilayers; D000644:Quaternary Ammonium Compounds; D015222:Sodium Channels; C022799:clofilium