PHARMACOLOGICAL PROPERTIES OF AXONAL SODIUM-CHANNELS IN THE COCKROACH PERIPLANETA-AMERICANA L .1. SELECTIVE BLOCK BY SYNTHETIC SAXITOXIN

  • 1 January 1979
    • journal article
    • research article
    • Vol. 83  (DEC) , 41-48
Abstract
Voltage-clamp experiments on isolated giant axons of the cockroach P. americana L. show that chemically synthesized saxitoxin [STX] specifically and reversibly blocks the transient inward Na current without affecting the steady-state outward K current. From the concentration dependence of Na current suppression it is concluded that individual Na channels are blocked by single molecules of synthetic STX which bind reversibly to part of the channel with a dissociation constant of 3.0 .times. 10-9 M. Synthetic STX blocks Na channels in cockroach axons at a lower concentration than tetrodotoxin. Na channel block by synthetic STX is more readily reversed than tetrodotoxin-induced block.