SPECIFIC 2ND MESSENGERS ACTIVATE THE CAUDAL PHOTORECEPTOR OF CRAYFISH

The caudal photoreceptor (CPR) found in the last abdominal ganglion of crayfish is a well-known example of a non-retinal photosensitive elem ent. In addition to light sensitivity, this cell has been assigned a c ommand role for a walking behavior. The molecular mechanism of transdu ction in this cell has not been previously studied. The involvement of an intermediate messenger substance is suggested by its long latency to response, its prolonged afterdischarge, and by the requirement for an amplification process for the efficient transduction of light. We t ested the effect of some putative second messengers by pressure inject ing them into the CPR and noting the physiological response. Here we r eport that intracellular injection of inositol 1,4,5-trisphosphate (IP 3), calcium, and the guanosine nucleotide GTP mimics the light respons e, while cAMP, IP1 and IP2 have no effect on the firing rate. The key intermediate in transduction in vertebrate photoreceptors, cGMP, was i neffective in this system. This work adds to the growing body of evide nce that IP3 plays a role in invertebrate phototransduction.