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J Neurophysiol (July 2, 2003). doi:10.1152/jn.00181.2003
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Submitted on February 26, 2003
Accepted on June 27, 2003

Calcium sensitivity of a sodium-activated non-selective cation channel in lobster olfactory receptor neurons

Yuriy V Bobkov1* and Barry W Ache2

1 Whitney Laboratory, University of Florida, St. Augustine, Florida, USA
2 Whitney Laboratory, University of Florida, St. Augustine, Florida, USA; Departments of Zoology and Neuroscience, Center for Smell and Taste, and McKnight Brain Institute, Gainesville, Florida, USA

* To whom correspondence should be addressed. E-mail: bobkov{at}whitney.ufl.edu.

We report that a Na+-activated non-selective cation channel described previously in lobster olfactory neurons (Zhainazarov et al. 1998), in which phosphoinositide signaling mediates olfactory transduction, can also be activated by Ca2+. Ca2+ activates the channel in the presence of Na+, increasing the open probability of the channel with a K1/2 of 490 nM and a Hill coefficient of 1.3. Ca2+ also increases the sensitivity of the channel to Na+. In some cells the same channel is Ca2+-insensitive in a cell-specific manner. The nonspecific activator of protein phosphatases, protamine, applied to the intracellular face of patches containing the channel irreversibly eliminates the sensitivity to Ca2+. This effect can be blocked by okadaic acid, a nonspecific blocker of protein phosphatases, and restored by the catalytic subunit of PKA in the presence of MgATP. The Ca2+-sensitive form of the channel is predominantly expressed in the transduction zone of the cells in situ. These findings imply that the Ca2+ sensitivity of the channel, and possibly its regulation by phosphorylation, play a role in olfactory transduction and help tie activation of the channel to the canonical phosphoinositide turnover pathway.




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