| Abstract: | Amino acids, olfactory stimuli for the channel catfish (Ictaluruspunctatus), were tested for the ability to affect cyclic AMPmetabolism in isolated olfactory cilia. Ten stimuli, representativeof each receptor subtype and covering a wide range of electrophysiologicalpotency, elicited similar increases in guanine nucleotide-dependentcyclic AMP formation. Stimulus-dependent activation of adenylatecyclase was observed only when receptor occupancy approachedor exceeded 50%. Stimulus activation of adenylate cyclase wasadditive with that obtained with guanine nucleotide alone, wasindependent of receptor specificity, and poorly correlated withneural potency. Stimuli did not affect cyclic nucleotide phosphodiesteraseactivity in isolated cilia preparations. Both cyclic AMP andcyclic GMP reversibly increased membrane conductance in isolatedciliary membranes incorporated in artificial phospholipid bilayers.The cyclic nucleotide-gated conductance was activated by eithernucleotide with equal potency, did not require exogenous ATPor GTP, and was mediated by 44 pS non-selective cation channels.Taken together, these results suggest that, under appropriateconditions of receptor occupancy, cyclic AMP links amino acidchemoreceptor binding to membrane depolarization by directlygating cation channels in olfactory cilia. |
