Sensory cells have evolved pathways that allow ion channels to be regulated by external stimuli such as movement, light, or chemicals. In some cases, such as in photoreceptors and olfactory and taste receptors, the means by which the external stimulus is transduced is reasonably well understood. Such cells appear to handle information in ways similar to those used by neurons that deal with information coming from a presynaptic pathway, by altering the levels of second messengers such as cyclic nucleotides, which then open or close ion channels in the plasma membrane. In contrast, in mechanoreceptors, which include touch receptors and hair cells of the cochlea that are required for hearing, movement is directly linked to the gating of ion channels.
Fluorophore‐Labeled Cyclic Nucleotides as Potent Agonists of Cyclic Nucleotide‐Regulated Ion Channels