The Native Rat Olfactory Cyclic Nucleotide-Gated Channel Is Composed of Three Distinct Subunits

Abstract

Cyclic nucleotide-gated (CNG) channels play central roles in visual and olfactory signal transduction. In the retina, rod photoreceptors express the subunits CNCα1 and CNCβ1a. In cone photoreceptors, only CNCα2 expression has been demonstrated so far. Rat olfactory sensory neurons (OSNs) express two homologous subunits, here designated CNCα3 and CNCα4. This paper describes the characterization of CNCβ1b, a third subunit expressed in OSNs and establishes it as a component of the native channel. CNCβ1b is an alternate splice form of the rod photoreceptor CNCβ1a subunit. Analysis of mRNA and protein expression together suggest co-expression of all three subunits in sensory cilia of OSNs. From single-channel analyses of native rat olfactory channels and of channels expressed heterologously from all possible combinations of the CNCα3, -α4, and -β1b subunits, we conclude that the native CNG channel in OSNs is composed of all three subunits. Thus, CNG channels in both rod photoreceptors and olfactory sensory neurons result from coassembly of specific α subunits with various forms of an alternatively spliced β subunit.