EFFECTS OF CA2+ ON ELECTRO-OLFACTOGRAM IN THE ISOLATED OLFACTORY MUCOSA OF THE FROG

Reports are conflicting as to whether the presence of Ca2+ on the ciliated surface of the olfactory mucosa suppresses or potentiates the response of receptor cells to odorants. To resolve this issue, electro-olfactograms (EOGs) were recorded from the isolated olfactory mucosae of the frog while its ciliated surface was perfused with saline solutions containing differing concentrations of Ca2+. A decrease in Ca2+ concentration augmented the EOG amplitude, and the magnitude of die augmentation increased as the Ca2+ concentration decreased progressively. The slow forskolin-induced change in potential likewise increased in amplitude with the removal of Ca2+ from the perfusate. Desensitization of EOG during the prolonged administration of odorants developed similarly, irrespective of the concentration of Ca2+ on the ciliated surface. These observations are consistent with findings of patch-clamp and biochemical experiments. The augmentation of EOG at low Ca2+ concentrations appeared to result from either an increase in activity of adenylate cyclase or an increase in responsiveness of the channels activated by adenosine 3',5'-cyclic monophosphate, but not from an increased sensitivity of the receptor molecules.