Cellular and molecular constituents of olfactory sensation in vertebrates.
Since the discovery of odorant-activated adenylate cyclase in the olfactory receptor cilia, research into the olfactory perception of vertebrates has rapidly expanded. Recent studies have shown how the odor discrimination starts at the receptor level: each of 700-1000 types of the olfactory neurons in the neural olfactory epithelium contains a single type of odor receptor protein. Although the receptors have relatively low specific affinities for odorants, excitation of different types of receptors forms an excitation pattern specific to each odorant in the glomerular layer of the olfactory bulb. It was demonstrated that adenosine 3',5'-cyclic monophosphate (cAMP) is very likely the sole second messenger for olfactory transduction. It was also demonstrated that the affinity of the cyclic nucleotide-gated channel for cAMP regulated by Ca(2+)/calmodulin is solely responsible for the adaptation of the cell. However, many other regulatory components were found in the transduction cascade. Regulated by Ca(2+) and/or the protein-phosphorylation, many of them may serve for the adaptation of the cell, probably on a longer time scale. It may be important to consider the resensitization as a part of this adaptation, as well as to collect kinetic data of each reaction to gain further insight into the olfactory mechanism.
Nakamura
T
T
Department of Applied Physics and Chemistry, Division of Bio-Informatics, Faculty of Electro-Communications, The University of Electro-Communications, Tokyo, Japan. tad@pc.uec.ac.jp
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels; D019204:GTP-Binding Proteins / Q000378:metabolism; D006162:Guanylate Cyclase / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D009831:Olfactory Mucosa / Q000166:cytology / Q000294:innervation; D009833:Olfactory Pathways / Q000166:cytology / Q000502:physiology*; D018034:Olfactory Receptor Neurons / Q000166:cytology / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction / Q000502:physiology; D012903:Smell / Q000502:physiology*; D014714:Vertebrates / Q000502:physiology*
D018118:Chloride Channels; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D015544:Inositol 1,4,5-Trisphosphate; D010727:Phosphoric Diester Hydrolases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D006162:Guanylate Cyclase; D002118:Calcium