Diversity of sodium channels in adult and cultured cells, in oocytes and in lipid bilayers.

Ionic channels in biological membranes enable the passive movement of ions between the extra- and intracellular solutions and are generally named after the main permeant ion. Thus open sodium channels are selective for Na + ions and have only minor permeability for other cations and anions. Such Na+-preferring channels are present in electrically excitable membranes of nerve and muscle and also in many inexcitable cells, e. g. epithelial cells (Fuchs et al. 1977; Palmer 1987) and light receptor cells of vertebrate eyes (Yau and Nakatani 1984; Hodgkin et al. 1985). However, this review and the following chapters in this volume are devoted exclusively to voltage-gated channels.