It is generally considered that olfactory receptors are GTP-binding protein coupled receptors (GCR). There is a possibility that lipids in addition to GCR are also involved in the odor reception. Olfactory receptor potential is induced by activation of cAMP-gated channels, IP-3gated channels or Ca2+ -activated Cl- -channels. In addition, a non-second messenger pathway greatly contributes to generation of in vivo olfactory responses.
The perception of odors begins with depolarization of the olfactory receptor cells. This transduction process is mediated by G-protein-linked activation of adenylate cyclase, which produces a membrane current by direct gating of cationic channels (cAMP-gated channels) located in ciliary plasma membrane. Opening of these cAMP-gated channels allows monovalent as well as divalent cations to enter the ciliary cytoplasm, and this Ca2+ influx serves two important functions. First, the Ca2+ influx activates a Cl- current, which stabilizes the transduction current during fluctuations in extracellular cation concentration and increases the total current activated by cAMP. Second, the Ca2+ influx mediates adaptation by providing negative feedback at several stages in the transduction mechanism.
This review summarizes recent progress on the knowledge of signal processing that occurs in the neuronal systems of olfactory epithelium and olfactory bulb. Emphasis is placed on the discussion related to the following working hypotheses: (1) Odor information received by odor receptor proteins expressed in a specific zone of the olfactory epithelium may be transmitted selectively to the target neurons in a corresponding zone of the olfactory bulb, and (2) Within each zone, olfactory sensory neurons expressing the same odor receptor protein may converge their axons onto one or a few common target glomeruli in the bulb.
Olfactory information may be tuned along the vertical axis in the olfactory bulb by means of synaptic interactions. The mitral cells have a relatively narrow odor spectrum. In addition, odors may be separated into individual chemical components in the deep olfactory bulb. A further tune of odors may be carried out in the superficial layer of the piriform cortex, whereas the tuned information would be reconstituted in the deep piriform cortex. The fact that neocortical neurons responded exclusively to biological odors could be speculated that selective olfactory information for animal's life needs would be in the neocortex during passing the thalamus.
Direct electron-transfer reactions of cytochrome c, ferredoxin and myoglobin at functional electrodes have been demonstrated and the functions of the suitable surfaces for the rapid electron-transfer have been discussed. Pyridyl promoter modified gold electrodes and positively charged polypeptide modified surfaces were effective for cytochrome c and ferredoxin, respectively. Highly hydrophilic surface of indium oxide electrodes gave well-defined voltammograms of both horse heart and sperm whale metmyoglobins. These functional electrodes are applicable to various bioelectrochemical measurements, to build up bioelectrocatalytic reactions with the aid of enzyme reactions, and to develop various electrofunctional devices on the basis of protein electrochemistry.
It is well-known that water plays a major role in a large number of biological processes in living systems and it is also commonly believed that the properties of water near interfaces are quite different from those of the bulk water by the interaction between water and interfaces. Living systems, such as cells and tissues are very rich in such interfaces due to the existence of the cellular cytoskeleton. While conducting 360MHz 1H-NMR studies on cross-relaxation phenomena in protein gel and solution, and in rat normal and hepatocellular tumor, we found that intermolecular cross-relaxation times (TIS) from irradiated protein protons to water protons are a sensitive parameter of water-macromolecule interaction and that TIS imaging could provide new information on the difference in the interaction of water with the macromolecule in vivo.