Abstract
It is well known that nitric oxide (NO) functions as a neurotransmitter: NO is produced by NO synthase (NOS) in postsynaptic nerves and diffuses through membranes into presynaptic ones to activate soluble guanylyl cyclase (sGC). This causes the production of cGMP, resulting in the feedback control of presynaptic nerve activity. In taste sensory systems, however, the NO-cGMP cascade might act differently. In vertebrate taste receptors, evidence for NOS expression, function of cGMP as a second messenger and regulation of the cGMP level by NO has been reported. These reports suggest that NO could participate in the signal transduction in the taste receptor cells. In gustatory receptor neurons of the blowfly, Phormia regina, the importance of cGMP in the sugar taste transduction has also been suggested. If cGMP is a second messenger of the sugar taste transduction, cGMP may be produced by NO-sensitive sGC in the sugar receptor neurons. In this paper, we review recent progresses in our study on the signal transduction including NO-cGMP cascade in the sugar receptor neurons of P. regina. Our study covers the analyses by electrophysiological recording as well as Ca2+/NO- imaging.
