In vertebrate olfactory neurons, odor molecules stimulate the opening of cyclic nucleotide-gated channels (CNGs). The resulting influx of Ca2+ ions also triggers a negative-feedback mechanism in which channel activity is inhibited when bound to a Ca2+-calmodulin (CaM) complex. This mechanism promotes olfactory adaptation and allows animals to evaluate the odor environment continually. Two groups have determined that two of the channel's three subunits are required for odor adaptation. Munger et al. show that channels from mice lacking the CNGA4 subunit exhibited slower Ca2+-CaM-mediated inhibition. Bradley et al. have used a heterologous expression system to show that both the CNGA4 and CNGB1b subunits facilitate Ca2+-CaM binding to the open state of channel.
S. D. Munger, A. P. Lane, H. Zhong, T. Leinders-Zufall, K.-W. Yau, F. Zufall, R. R. Reed, Central role of the CNGA4 channel subunit in Ca2+-calmodulin-dependent odor adaptation. Science 294, 2172-2175 (2001). [Online Journal]
J. Bradley, D. Reuter, S. Frings, Facilitation of calmodulin-mediated odor adaptation by cAMP-gated channel subunits. Science 294, 2176-2178 (2001). [Online Journal]