A new tetrahydro-β-carboline, trypargine (TRG), specifically suppresses the Na current (INa) when applied to the internal surface of the squid axon membrane without affecting the K current (IK). The binding of TRG to its receptor is potential-dependent and occurs at a site about halfway through the membrane electric field from the outside; the dissociation constant is 11μM at 0mV.
