T. Leinderszufall et al., CALCIUM-ENTRY THROUGH CYCLIC NUCLEOTIDE-GATED CHANNELS IN INDIVIDUAL CILIA OF OLFACTORY RECEPTOR-CELLS - SPATIOTEMPORAL DYNAMICS, The Journal of neuroscience, 17(11), 1997, pp. 4136-4148
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.