title: Presynaptic external calcium signaling involves the calcium-sensing receptor in neocortical nerve terminals.
abstract: BACKGROUND
  Nerve terminal invasion by an axonal spike activates voltage-gated channels, triggering calcium entry, vesicle fusion, and release of neurotransmitter. Ion channels activated at the terminal shape the presynaptic spike and so regulate the magnitude and duration of calcium entry. Consequently characterization of the functional properties of ion channels at nerve terminals is crucial to understand the regulation of transmitter release. Direct recordings from small neocortical nerve terminals have revealed that external [Ca(2+)] ([Ca(2+)](o)) indirectly regulates a non-selective cation channel (NSCC) in neocortical nerve terminals via an unknown [Ca(2+)](o) sensor. Here, we identify the first component in a presynaptic calcium signaling pathway.
  
  
  RESULTS
  By combining genetic and pharmacological approaches with direct patch-clamp recordings from small acutely isolated neocortical nerve terminals we identify the extracellular calcium sensor. Our results show that the calcium-sensing receptor (CaSR), a previously identified G-protein coupled receptor that is the mainstay in serum calcium homeostasis, is the extracellular calcium sensor in these acutely dissociated nerve terminals. The NSCC currents from reduced function mutant CaSR mice were less sensitive to changes in [Ca(2+)](o) than wild-type. Calindol, an allosteric CaSR agonist, reduced NSCC currents in direct terminal recordings in a dose-dependent and reversible manner. In contrast, glutamate and GABA did not affect the NSCC currents.
  
  
  CONCLUSIONS
  Our experiments identify CaSR as the first component in the [Ca(2+)](o) sensor-NSCC signaling pathway in neocortical terminals. Decreases in [Ca(2+)](o) will depress synaptic transmission because of the exquisite sensitivity of transmitter release to [Ca(2+)](o) following its entry via voltage-activated Ca(2+) channels. CaSR may detects such falls in [Ca(2+)](o) and increase action potential duration by increasing NSCC activity, thereby attenuating the impact of decreases in [Ca(2+)](o) on release probability. CaSR is positioned to detect the dynamic changes of [Ca(2+)](o) and provide presynaptic feedback that will alter brain excitability.
authors.affiliation: Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: Wenyan
authors.initials: W
authors.lastname: Chen
authors.forename: Jeremy B
authors.initials: JB
authors.lastname: Bergsman
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wang
authors.forename: Gawain
authors.initials: G
authors.lastname: Gilkey
authors.forename: Carol-Renée
authors.initials: CR
authors.lastname: Pierpoint
authors.forename: Erin A
authors.initials: EA
authors.lastname: Daniel
authors.forename: Emmanuel M
authors.initials: EM
authors.lastname: Awumey
authors.forename: Philippe
authors.initials: P
authors.lastname: Dauban
authors.forename: Robert H
authors.initials: RH
authors.lastname: Dodd
authors.forename: Martial
authors.initials: M
authors.lastname: Ruat
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Smith
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001483:Base Sequence; D020013:Calcium Signaling; D002460:Cell Line; D017931:DNA Primers; D004305:Dose-Response Relationship, Drug; D005260:Female; D005971:Glutamates / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051379:Mice; D009281:Naphthalenes / Q000494:pharmacology; D019579:Neocortex / Q000378:metabolism*; D009411:Nerve Endings / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing / Q000819:agonists / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: C506457:(R)-2-(1-(1-naphthyl)ethyl-aminom-ethyl)indole; D017931:DNA Primers; D005971:Glutamates; D007211:Indoles; D009281:Naphthalenes; D044169:Receptors, Calcium-Sensing; D005680:gamma-Aminobutyric Acid