Direct suppression by odorants of cyclic nucleotide-gated currents in the newt photoreceptors

Odorants are known to suppress the cyclic nucleotide-gated (CNG) current in olfactory receptor cells. It is unclear, however, whether odorants suppres s the olfactory CNG current directly or whether they suppress the current b y decreasing the second messenger (cAMP) through the activation of phosphod iesterase. We found that odorants also suppress CNG currents in photoreccpt or cells. Under voltage clamp, an odorant puff immediately suppressed the c urrents induced by the intracellular cGMP in isolated newt rods and cones. Odorants also suppressed the currents induced by another cGMP analog (8-p-c hlorophenylthio-cGMP, which strongly resists hydrolysis by phosphodiesteras e), suggesting that the second messenger metabolism via phosphodiesterase i s not involved in the suppression by odorants. This suggests that odorants suppress the CNG currents directly rather than via the second messenger sys tem in photoreceptors, and also likely in olfactory receptor cells. (C) 200 0 Elsevier Science B.V. All rights reserved.