A tale of two senses

It has been about a decade since the molecular basis of the excitatory pathway in vertebrate photoreceptors was resolved. The lessons learned from that achievement have now been applied to other sensory modalities. The belief that each sensory modality relies upon unique, specialized molecules seems no longer tenable. Instead, common molecular components are adapted as needed and may function not only in sensory transduction but in axon outgrowth, desensitization, and trophic support of receptive cells. An appreciation of thiscommonality provided the incentive for the Soehringer lngelheim Fonds International Conference on Signal Transduction in Vision and the Chemical Senses, held in Titisee, Germany, March 22-26, 1995. The success of this approach was demonstrated by the lively and critical discussions between individuals from differing sensory persuasions, Sessions were held on vertebrate and invertebrate photoreception, olfaction, and taste, as well as chemical signaling in unicellular organisms and sperm. Mutual interests extended far beyond the study of the family of receptor proteins with seven transmembrane domains, to include cyclic nucleotidegated (CNG) channels, inositol-1,4,5trisphosphate (IPs) receptors, G protein receptor kinases, the arrestin gene family, and phosphodiesterases. However, investigations into each sensory modality are at different stages in their evolution. While much of the meeting debated mechanisms by which sensory receptors are activated, the vertebrate photoreceptor session centered upon turn-off and adaptation mechanisms. We will begin with a review of sessions dealing with how sensory receptors are excited.