CALCIUM-ENTRY THROUGH CYCLIC NUCLEOTIDE-GATED CHANNELS IN INDIVIDUAL CILIA OF OLFACTORY RECEPTOR-CELLS - SPATIOTEMPORAL DYNAMICS

Transient elevations of intracellular Ca2+ play an important role in r egulating the sensitivity of olfactory transduction, but such elevatio ns have not been demonstrated in the olfactory cilia, which are the si te of primary odor transduction. To begin to understand Ca2+ signaling in olfactory cilia, we used high-resolution imaging techniques to stu dy the Ca2+ transients that occur in salamander olfactory receptor neu rons (ORNs) as a result of cyclic nucleotide-gated (CNG) channel activ ation. To visualize ciliary Ca2+ signals, we loaded ORNs with the Ca2 indicator dye Fluo-3 AM and measured fluorescence with a laser scanni ng confocal microscope. Application of the phosphodiesterase inhibitor IBMX increased fluorescence in the cilia and other neuronal compartme nts; the ciliary signal occurred first and was more transient. This si gnal could be abolished by lowering external Ca2+ or by applying LY835 83, a potent blocker of CNG channels, indicating that Ca2+ entry throu gh CNG channels was the primary source of fluorescence increases. Dire ct activation of CNG channels with low levels of 8-Br-cGMP (1 mu M) le d to tonic Ca2+ signals that were restricted locally to the cilia and the dendritic knob. Elevated external K+, which depolarizes cell membr anes, increased fluorescence signals in the cell body and dendrite but failed to increase ciliary Ca2+ fluorescence. The results demonstrate the existence and spatiotemporal properties of Ca2+ transients in ind ividual olfactory cilia and implicate CNG channels as a major pathway for Ca2+ entry into ORN cilia during odor transduction.