High-affinity cAMP phosphodiesterase and adenosine localized in sensory organs.

Odorant-stimulated formation of cAMP in olfactory receptor neurons may mediate olfactory signal transduction. The response is short and desensitization occurs rapidly, possibly by induction of cyclic nucleotide phosphodiesterase (PDE) activity. Previously, we showed that two low Km PDEs regulate hydrolysis of cAMP in olfactory cilia. One PDE is Ca2+/calmodulin-dependent and non-selective for both cAMP-PDE and cGMP; the other is Ca2+/calmodulin-independent, sensitive to rolipram and selective for cAMP. We have localized cAMP-selective PDE in olfactory, gustatory and retinal sensory systems by autoradiography with the selective inhibitor [3H]rolipram. We observe dense binding over olfactory neurons, particularly over olfactory nerve bundles and olfactory cilia. In the tongue apical regions of taste buds of the circumvallate papillae are strongly labeled as well as portions of the glossopharyngeal nerve. Retinal binding is most dense over the inner plexiform layer, ganglion cells and the optic nerve but is also substantial over the inner nuclear layer. The pattern of [3H]rolipram-binding in retina is reminiscent of adenosine localization. Accordingly, adenosine was immunohistochemically localized in olfactory, gustatory and retinal tissues. Adenosine immunoreactivity is observed in olfactory neurons, in the basal regions of taste buds and in retinal ganglion cells.