Presynaptic external calcium signaling involves the calcium-sensing receptor in neocortical nerve terminals.
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.
Chen
Wenyan
W
Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
Bergsman
Jeremy B
JB
Wang
Xiaohua
X
Gilkey
Gawain
G
Pierpoint
Carol-Renée
CR
Daniel
Erin A
EA
Awumey
Emmanuel M
EM
Dauban
Philippe
P
Dodd
Robert H
RH
Ruat
Martial
M
Smith
Stephen M
SM
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
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