Limits of calcium clearance by plasma membrane calcium ATPase in olfactory cilia.
BACKGROUND
In any fine sensory organelle, a small influx of Ca(2+) can quickly elevate cytoplasmic Ca(2+). Mechanisms must exist to clear the ciliary Ca(2+) before it reaches toxic levels. One such organelle has been well studied: the vertebrate olfactory cilium. Recent studies have suggested that clearance from the olfactory cilium is mediated in part by plasma membrane Ca(2+)-ATPase (PMCA).


RESULTS
In the present study, electrophysiological assays were devised to monitor cytoplasmic free Ca(2+) in single frog olfactory cilia. Ca(2+) was allowed to enter isolated cilia, either through the detached end or through membrane channels. Intraciliary Ca(2+) was monitored via the activity of ciliary Ca(2+)-gated Cl(-) channels, which are sensitive to free Ca(2+) from about 2 to 10 microM. No significant effect of MgATP on intraciliary free Ca(2+) could be found. Carboxyeosin, which has been used to inhibit PMCA, was found to substantially increase a ciliary transduction current activated by cyclic AMP. This increase was ATP-independent.


CONCLUSIONS
Alternative explanations are suggested for two previous experiments taken to support a role for PMCA in ciliary Ca(2+) clearance. It is concluded that PMCA in the cilium plays a very limited role in clearing the micromolar levels of intraciliary Ca(2+) produced during the odor response.
Kleene
Steven J
SJ
Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio, United States of America. steve@syrano.acb.uc.edu
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002923:Cilia / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism; D009833:Olfactory Pathways; D018034:Olfactory Receptor Neurons / Q000201:enzymology*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism*; D011894:Rana pipiens / Q000378:metabolism
D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium