Plasma membrane Ca(2+)-ATPase in the cilia of olfactory receptor neurons: possible role in Ca(2+) clearance.
Olfactory sensory neurons respond to odorants increasing Ca(2+) concentrations in their chemosensory cilia. Calcium enters the cilia through cAMP-gated channels, activating Ca(2+)-dependent chloride or potassium channels. Calcium also has a fundamental role in odour adaptation, regulating cAMP turnover rate and the affinity of the cyclic nucleotide-gated channels for cAMP. It has been shown that a Na(+)/Ca(2+) exchanger (NCX) extrudes Ca(2+) from the cilia. Here we confirm previous evidence that olfactory cilia also express plasma membrane Ca(2+)-ATPase (PMCA), and show the first evidence supporting a role in Ca(2+) removal. Both transporters were detected by immunoblot of purified olfactory cilia membranes. The pump was also revealed by immunocytochemistry and immunohistochemistry. Inside-out cilia membrane vesicles transported Ca(2+) in an ATP-dependent fashion. PMCA activity was potentiated by luminal Ca(2+) (K(0.5) = 670 nm) and enhanced by calmodulin (CaM; K(0.5) = 31 nm). Both carboxyeosin (CE) and calmidazolium reduced Ca(2+) transport, as expected for a CaM-modulated PMCA. The relaxation time constant (tau) of the Ca(2+)-dependent Cl(-) current (272 +/- 78 ms), indicative of luminal Ca(2+) decline, was increased by CE (2181 +/- 437 ms), by omitting ATP (666 +/- 49 ms) and by raising pH (725 +/- 65 ms), suggesting a role of the pump on Ca(2+) clearance. Replacement of external Na(+) by Li(+) had a similar effect (tau = 442 +/- 8 ms), confirming the NCX involvement in Ca(2+) extrusion. The evidence suggests that both Ca(2+) transporters contribute to re-establish resting Ca(2+) levels in the cilia following olfactory responses.
Castillo
Karen
K
Department of Biology, Faculty of Sciences and Millennium Institute for Cell Dynamics and Biotechnology, University of Chile, Santiago, Chile.
Delgado
Ricardo
R
Bacigalupo
Juan
J
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002025:Bufonidae; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology*; D002923:Cilia / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D018034:Olfactory Receptor Neurons / Q000187:drug effects / Q000201:enzymology*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012903:Smell / Q000187:drug effects / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000187:drug effects / Q000378:metabolism; D013347:Subcellular Fractions
D002147:Calmodulin; D004791:Enzyme Inhibitors; D019831:Sodium-Calcium Exchanger; D000255:Adenosine Triphosphate; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium