Biophysics of CNG Ion Channels

Abstract

Cyclic nucleotide-gated (CNG) ion channels are cation-selective, opened by intracellular cyclic nucleotides like cAMP and cGMP, and present in many differ- ent neurons and non-neuronal cells. This chapter will concentrate primarily on the biophysical aspects of retinal and olfactory CNG channels, with special reference to ion permeation and selectivity and their underlying molecular basis, and will include a brief overview of the physiological function of CNG channels in both olfaction and phototransduction. We will review the subunit composition and molecular structure of the CNG channel and its similarity to the closely related potassium channels, and will also briefly outline the currently accepted molecular basis underlying activation of the channel and the location of the channel 'gate'. We will then outline some gen- eral methodologies for investigating ion permeation and selectivity, before reviewing the ion permeation and selectivity properties of native and recombinant CNG chan- nels. We will discuss divalent ion permeation through the channel and the mechanism of channel block by divalent ions. The chapter will conclude by discussing the results