A study of rat olfactory mechanisms
Membranes prepared from the olfactory mucosa of the rat show a high level of adenylate cyclase activity, typically 500 pmol/min/mg protein. The activity increases in the presence of odorants and is inhibited by calcium. Linkage of receptor to cyclase seems to be mediated by a G-protein. The existence of an odorant-stimulated adenylate cyclase in the rat is discussed. The olfactory tissue is found to contain high levels of intracellular cyclic AMP (ca. 40 pmoles/mg protein), almost twice that found in the brain tissue. Odorants appear to have no effect on these levels. The role of lipids in olfaction is investigated. The olfactory epithelium is found to be a rich source of phospholipids, comprising approximately 80% of the total lipids. The phospholipids identified are PC, PE, PS, SM, PA, PI, PIP, PIP=, accounting for approximately 41,23,9,11,4,10,2, and 2%, respectively, of the total phospholipids. 32P orthophosphate is incorporated into all the phospholipids; PIP and PIP2 show the highest rate of incorporation. Attempts are made to investigate the effect of odorants on this rate of incorporation. The fatty acid profile of the rat olfactory phospholipids is found not to be unique to the olfactory tissue. Elaidic acid 81:1t [n-9], however, seems to be present in higher concentrations than observed in other tissues. The fatty acids identified are 14:0, 15:0, 16:0, 16:1[n-9], 17:0, 18:0, 18:1c[n-9], 18:1t [n-9], 18:2[n-6], 20:0, 20:3[n-6], 20:4[n-6], 20:5[n-3], 22:0, 22:4[n-6], 22:5[n-6], 22:5[n-3], 22:6[n-3], 24:0, and 24:1[n-9].