IMAGING ODOR-INDUCED CALCIUM TRANSIENTS IN SINGLE OLFACTORY CILIA - SPECIFICITY OF ACTIVATION AND ROLE IN TRANSDUCTION

The possibility that odor stimuli trigger distinct Ca2+ elevations wit hin the cilia of vertebrate olfactory receptor neurons (ORNs) is a wid ely proposed concept. However, because of the small size of the olfact ory cilia, the existence and properties of such Ca2+ elevations and th eir role in odor transduction are still unknown. We investigate odor-i nduced Ca2+ changes in individual olfactory cilia from salamander usin g the Ca2+ indicator dye fluo-3 in combination with laser scanning con focal microscopy. Single brief applications of odor ligand produce hig hly localized Ca2+ elevations in individual cilia lasting for several seconds. These Ca2+ signals originate in the cilia and depend entirely on Ca2+ entry through ciliary cyclic nucleotide-gated ion channels. T he odor specificity of the Ca2+ rises implies a receptor-operated mech anism underlying odor detection. Each of the cilia on a receptor neuro n functions as an independent biochemical compartment that can detect odorants and produce a Ca2+ transient with remarkably uniform properti es in terms of kinetics and odor specificity. The rate of recovery of the odor-induced Ca2+ transients matches recovery from a short-term fa rm of odor adaptation. Application of the membrane-permeant intracellu lar Ca2+ chelator BAPTA AM eliminates this odor adaptation. The result s indicate that an olfactory cilium serves as a basic functional unit at the input level of the olfactory system, controlling both the speci ficity and sensitivity of odor detection.