BETA-SUBUNITS OF THE OLFACTORY CYCLIC NUCLEOTIDE-GATED CHANNEL FORM ANITRIC-OXIDE ACTIVATED CA2+ CHANNEL

Cyclic nucleotide-gated channels are important in visual and olfactory transduction, and possibly in other neuronal functions. These channel s have a complex permeability to Ca2+ ions that may be important in th eir cellular functions. They are composed of two different subunits, a lpha and beta, that have been cloned and expressed, but the beta subun it alone cannot be activated by cyclic nucleotides, confounding the an alysis of its characteristics. However, we found that nitric oxide can activate the homomeric expressed beta subunit, and the resulting chan nel possesses many properties of the L-type Ca2+ channels, including h igh permeability to Ca2+ ions and sensitivity to Ca2+ channel blockers . Thus, the Ca2+ permeability characteristics of native channels are m ostly conferred by properties of the beta subunit, and the beta subuni t alone can act as a NO-sensitive Ca2+ channel. A nearly identical con ductance activated by NO is present in the membrane of rat vomeronasal neurons, indicating that homomeric beta channels exist in vivo.