title: Targeted expression of anoctamin calcium-activated chloride channels in rod photoreceptor terminals of the rodent retina.
abstract: OBJECTIVE
  In the vertebrate retina, calcium-activated chloride channels are expressed in photoreceptor synaptic terminals. These channels are involved in the control of transmitter release in the dark. The search for their molecular identity has recently lead to the localization of the protein anoctamin 2 (also TMEM16B) in the outer plexiform layer of the rodent retina. Since both rod and cone photoreceptors have their terminals in this layer, it was not clear which of these express anoctamin 2. Here, we examine rod spherules and cone pedicles for expression of anoctamin 2.
  
  
  METHODS
  Expression of anoctamin genes was studied in the rat eye using RT-PCR. Immunohistochemical experiments were used to localize anoctamins and chloride transporters with their regulatory kinases. Photoreceptor synaptic proteins, as well as the lectins Peanut agglutinin and Griffonia simplicifolia agglutinin, were used to distinguish retinal structures.
  
  
  RESULTS
  Anoctamin 1, 2, and 10 were found to be expressed in the eye. Anoctamin 2 was expressed as a splice variant that includes exon 15 of the genomic structure. The protein is exclusively expressed in rod terminals and is not present in cone pedicles. Expression is not clustered at the ribbon complex, but spread across the presynaptic membrane where it colocalizes with the plasma membrane calcium pump. The electroneutral chloride transporter NKCC1 is expressed in photoreceptor terminals, together with its regulatory kinases SPAK and OSR1.
  
  
  CONCLUSIONS
  Rod photoreceptor terminals possess the molecular machinery for chloride accumulation and for the generation of calcium-dependent chloride currents conducted through anoctamin 2 channels. We discuss this finding in the framework of the established hypothesis that calcium-activated chloride channels are part of a feedback inhibition mechanism that limits transmitter release in the dark.
authors.affiliation: Department of Molecular Physiology, Heidelberg University, Heidelberg, Germany.
authors.forename: Kristin
authors.initials: K
authors.lastname: Dauner
authors.forename: Carolin
authors.initials: C
authors.lastname: Möbus
authors.forename: Stephan
authors.initials: S
authors.lastname: Frings
authors.forename: Frank
authors.initials: F
authors.lastname: Möhrlen
mesh_terms: D000818:Animals; D000075369:Anoctamin-1; D000075368:Anoctamins; D015153:Blotting, Western; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation / Q000502:physiology*; D006168:Guinea Pigs; D017729:Presynaptic Terminals / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2
chemical_list: C552942:ANO1 protein, rat; C575623:Ano2 protein, rat; D000075369:Anoctamin-1; D000075368:Anoctamins; D018118:Chloride Channels; D017931:DNA Primers; D012333:RNA, Messenger; C578879:Slc12a2 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D011494:Protein Kinases; C116037:PAS domain kinases; C506604:Oxsr1 protein, rat; D017346:Protein Serine-Threonine Kinases
keywords: anoctamin; chloride; rod terminals