title: Optical control of calcium-regulated exocytosis.
abstract: BACKGROUND
  Neurons signal to each other and to non-neuronal cells as those in muscle or glands, by means of the secretion of neurotransmitters at chemical synapses. In order to dissect the molecular mechanisms of neurotransmission, new methods for directly and reversibly triggering neurosecretion at the presynaptic terminal are necessary. Here we exploit the calcium permeability of the light-gated channel LiGluR in order to reversibly manipulate cytosolic calcium concentration, thus controlling calcium-regulated exocytosis.
  
  
  METHODS
  Bovine chromaffin cells expressing LiGluR were stimulated with light. Exocytic events were detected by amperometry or by whole-cell patch-clamp to quantify membrane capacitance and calcium influx.
  
  
  RESULTS
  Amperometry reveals that optical stimulation consistently triggers exocytosis in chromaffin cells. Secretion of catecholamines can be adjusted between zero and several Hz by changing the wavelength of illumination. Differences in secretion efficacy are found between the activation of LiGluR and native voltage-gated calcium channels (VGCCs). Our results show that the distance between sites of calcium influx and vesicles ready to be released is longer when calcium influx is triggered by LiGluR instead of native VGCCs.
  
  
  CONCLUSIONS
  LiGluR activation directly and reversibly increases the intracellular calcium concentration. Light-gated calcium influx allows for the first time to control calcium-regulated exocytosis without the need of applying depolarizing solutions or voltage clamping in chromaffin cells.
  
  
  CONCLUSIONS
  LiGluR is a useful tool to study the secretory mechanisms and their spatiotemporal patterns in neurotransmission, and opens a window to study other calcium-dependent processes such as muscular contraction or cell migration.
authors.affiliation: Institute for Bioengineering of Catalonia (IBEC), 15-21 Baldiri Reixac, 08028 Barcelona, Spain.
authors.forename: Mercè
authors.initials: M
authors.lastname: Izquierdo-Serra
authors.forename: Dirk
authors.initials: D
authors.lastname: Trauner
authors.forename: Artur
authors.initials: A
authors.lastname: Llobet
authors.forename: Pau
authors.initials: P
authors.lastname: Gorostiza
mesh_terms: D000200:Action Potentials / Q000502:physiology / Q000528:radiation effects*; D000256:Adenoviridae / Q000235:genetics; D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D025802:Electric Capacitance; D005089:Exocytosis / Q000502:physiology / Q000528:radiation effects*; D015870:Gene Expression / Q000528:radiation effects; D005822:Genetic Vectors; D008027:Light; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D061251:Primary Cell Culture; D017470:Receptors, Glutamate / Q000235:genetics / Q000378:metabolism*; D009435:Synaptic Transmission / Q000528:radiation effects*
chemical_list: D015220:Calcium Channels; D002395:Catecholamines; C508971:LiGluR receptor; D017470:Receptors, Glutamate; D002118:Calcium