Batrachotoxin, a Selective Probe for Channels Modulating Sodium Conductances in Electrogenic Membranes

Abstract

One of the major challenges of modern neurobiology is the elucidation of the molecular mechnisms involved in the control of ion fluxes across excitable membranes of nerves and muscles, both at rest and during electrogenic activity. A key to an understanding of the nature and control of the membrane macromolecules which modulate ionic conductances has been the discovery and pharmacological charater-ization of various toxins which interact with specific components of the membrane entities which regulate ionic permeability. Although poorly understood, these membrane entities probably consist of macromolecules which bridge the membrane and directly control the ionic conductance. In some cases, there is an associated regulatory unit such as the acetylcholine receptor. The macromolecular unit controlling the ionic conductance has been referred to as a channel, ionophore or ion conductance modulator. In the present review, we shall deal with phenomena which are generally felt to be mechanistically consonant with the presence of channel whose functional activity is regulated by ‘gates’ rather than with phenomena involving some carrier molecule. The term channel will, therefore, be used in this review in referring to the membrane entity which modulates ionic conductances.