ODORANT-REGULATED CA2+ GRADIENTS IN RAT OLFACTORY NEURONS

Olfactory neurons respond to odors with a change in conductance that m ediates an influx of cations including Ca2+. The concomitant increase in [Ca(i)] has been postulated to play a role in the adaptation to mai ntained odorant stimulation (Kurahashi, T., and T. Shibuya. 1990. Brai n Research. 515:261-268. Kramer, R. H., and S. A. Siegelbaum. 1992. Ne uron. 9:897-906. Zufall, F., G. M. Shepherd, and S. Firestein. 1991. P roceedings of the Royal Society of London, B. 246:225-230.) We have im aged the distribution of [Ca(i)] in rat olfactory neurons (RON) using the Ca2+ indicator fura-2. A large percentage of the RON (42%, n = 35) responded to odorants with an increase in [Ca(i)]. About half of the responding neurons displayed an increase in [Ca(i)] at the apical end of the cell, but not at the soma. Moreover, in those cells that respon ded to odors with a standing [Ca(i)] gradient, the gradient could be m aintained for long periods of time (minutes) provided that the cells w ere continuously stimulated. In contrast, K+-induced depolarization el icited a more homogeneous increase in [Ca(i)]. The spatially inhomogen eous increase in [Ca(i)] elicited by odorants in some cells has import ant implications for the role of Ca2+ in adaptation because channels a nd enzymes regulated by Ca2+ will be affected differently depending on their location.