Ca²⁺-Activated Non-Selective Cation Channels

Abstract

Non-selective cation channels form a mixed group of ion channels including ligand-gated, hyperpolarization-activated, mechanosensitive channels, as well as channels activated by noxious stimuli or involved in capacitative Ca’ entry (see SIEMEN and HESCHELER 1993; ZHU et al. 1996; CATERINA et al. 1997; GAUSS et al. 1998; LUDWIG et al. 1998). Non-selective cation channels of the CaZ+activated type (NSCca) were described very shortly after the development of the patch-clamp technique (HAMILL et al. 1981), probably because these channels, usually closed in intact cells, activate spontaneously upon excision when the internal side of the channel comes into contact with millimolar concentrations of calcium. Many of their biophysical and regulatory properties have been described, but these channels remain something of an enigma because their molecular sequence has not been elucidated (see however SuzuKI et al. 1998), and channel function is unknown in many cases. Reviews on NSCca channels appeared elsewhere (PARTRIDGE and SWANDULLA 1988; SIEMEN and HESCHELER 1993; CONLEY 1996). A different type of non-selective, CaZ+activated cation channel, which depends on nicotinamide-adeninedinucleotide, has been reported in insulinoma cells (HERSON et al. 1997).