CA2--DEPENDENCE OF THE TURTLE OLFACTORY RESPONSE TO ODORANTS AND FORSKOLIN( AND CL)

In the turtle olfactory system, large responses to odorants appeared a fter application of cAMP or forskolin at high concentrations to the is olated olfactory receptor neurons or the olfactory epithelium, suggest ing that a cAMP-independent pathway greatly contributes to the generat ion of odor responses. We measured the effects of the mucosal Ca2+ and Cl- concentrations and a Ca2+-activated Cl--channel blocker, 4-acetam ide-4'-(isothiocyano) stilbene-2,2'-disulphonic acid (SITS), upon olfa ctory bulbar responses to explore the contribution of the Ca2+-activat ed Cl--channels to cAMP-dependent and independent pathways. Eliminatio n of mucosal Ca2+ by addition of 2 mM EGTA to the stimulating solution partially inhibited the cAMP-independent responses to 0.1 mM citralva but did not affect those to 0.1 mM lilial or 0.1 mM l-carvone. Substi tution of mucosal Cl- with gluconate slightly enhanced the total respo nse to 0.1 mM citralva but practically did not affect the responses to other odorants tested. SITS (2 mM) partially inhibited the responses to 50 mu M forskolin and 0.1 mM citralva but did not affect the cAMP-i ndependent response to 0.1 mM citralva in Ca2+-free Ringer's solution. These results suggested that the Ca2+-activated Cl- channels do not c ontribute to the generation of the cAMP-independent responses, but tha t they partially contribute to the generation of the cAMP-dependent re sponses in the turtle.