EFFECTS OF CA2-CYCLASE ACTIVITY IN SHEEP OLFACTORY EPITHELIUM( AND CALMODULIN ON ADENYLYL)

Sheep olfactory epithelium contains an adenylyl cyclase which is stimu lated by many but not all odorants. Here we report that this enzyme is activated by calmodulin in a dose-dependent manner, and that calcium ions are required for this response. Odorant stimulation of adenylyl c yclase is unaffected by the complex Ca2+-/calmodulin, as suggested by the results obtained both in Ca2+/calmodulin-depleted membranes and un der calmodulin antagonist treatment; this confirms the prediction that the Ca2+ binding protein and odorants stimulate the olfactory adenyly l cyclase through parallel mechanisms. The persistent activation of th e regulatory component of adenylyl cyclase by GppNHp does not alter th e response of the enzyme to either odorant or Ca2+/calmodulin. In shee p olfactory epithelium a cAMP-phosphodiesterase activity is also prese nt, which is highly inhibited by IBMX and aminophylline, scarcely by R O 20-1724, and unaffected by Ca2+/calmodulin. The modulatory role exer ted by calcium on cAMP system in sheep olfactory signal transduction i s discussed.