Calcium sensitivity of a sodium-activated nonselective cation channel in lobster olfactory receptor neurons.
We report that a Na+-activated nonselective cation channel described previously in lobster olfactory neurons, 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 protein kinase A 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.
Bobkov
Yuriy V
YV
Whitney Laboratory, University of Florida, Gainesville, Florida 32601, USA. bobkov@whitney.ufl.edu
Ache
Barry W
BW
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D018034:Olfactory Receptor Neurons / Q000187:drug effects / Q000502:physiology*; D033521:Palinuridae / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels; D012964:Sodium; D002118:Calcium