Molecular components of signal amplification in olfactory sensory cilia.
The mammalian olfactory system detects an unlimited variety of odorants with a limited set of odorant receptors. To cope with the complexity of the odor world, each odorant receptor must detect many different odorants. The demand for low odor selectivity creates problems for the transduction process: the initial transduction step, the synthesis of the second messenger cAMP, operates with low efficiency, mainly because odorants bind only briefly to their receptors. Sensory cilia of olfactory receptor neurons have developed an unusual solution to this problem. They accumulate chloride ions at rest and discharge a chloride current upon odor detection. This chloride current amplifies the receptor potential and promotes electrical excitation. We have studied this amplification process by examining identity, subcellular localization, and regulation of its molecular components. We found that the Na(+)/K(+)/2Cl(-) cotransporter NKCC1 is expressed in the ciliary membrane, where it mediates chloride accumulation into the ciliary lumen. Gene silencing experiments revealed that the activity of this transporter depends on the kinases SPAK and OSR1, which are enriched in the cilia together with their own activating kinases, WNK1 and WNK4. A second Cl(-) transporter, the Cl(-)/HCO(3)(-) exchanger SLC4A1, is expressed in the cilia and may support Cl(-) accumulation. The calcium-dependent chloride channel TMEM16B (ANO2) provides a ciliary pathway for the excitatory chloride current. These findings describe a specific set of ciliary proteins involved in anion-based signal amplification. They provide a molecular concept for the unique strategy that allows olfactory sensory neurons to operate as efficient transducers of weak sensory stimuli.
Department of Molecular Physiology, University of Heidelberg, 69120 Heidelberg, Germany.
Thomas
T
Hengl
Hiroshi
H
Kaneko
Kristin
K
Dauner
Kerstin
K
Vocke
Stephan
S
Frings
Frank
F
Möhrlen
D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002712:Chlorides / Q000378:metabolism; D002923:Cilia / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D025461:Feedback, Physiological; D020868:Gene Silencing; D017136:Ion Transport; D051379:Mice; D008822:Mice, Transgenic; D015778:Minor Histocompatibility Antigens; D008959:Models, Neurological; D018034:Olfactory Receptor Neurons / Q000502:physiology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D018035:Receptors, Odorant / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D012903:Smell / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2; D000076204:WNK Lysine-Deficient Protein Kinase 1
D001457:Anion Exchange Protein 1, Erythrocyte; D002712:Chlorides; D017931:DNA Primers; D015778:Minor Histocompatibility Antigens; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018035:Receptors, Odorant; C578878:Slc12a2 protein, mouse; C578879:Slc12a2 protein, rat; C523515:Slc4a1 protein, mouse; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D011494:Protein Kinases; C499024:Prkwnk4 protein, mouse; C486407:Stk39 protein, mouse; C499025:Wnk4 protein, rat; C116037:PAS domain kinases; C534421:OXSR1 protein, mouse; C506604:Oxsr1 protein, rat; D017346:Protein Serine-Threonine Kinases; D000076204:WNK Lysine-Deficient Protein Kinase 1; C498744:Wnk1 protein, mouse; C410410:Wnk1 protein, rat