The dynamic range and domain-specific signals of intracellular calcium in photoreceptors

Neuroscience. 2006 Aug 11;141(1):143-55. doi: 10.1016/j.neuroscience.2006.03.054. Epub 2006 May 6.

Abstract

Vertebrate photoreceptors consist of strictly delimited subcellular domains: the outer segment, ellipsoid, cell body and synaptic terminal, each hosting crucial cellular functions, including phototransduction, oxidative metabolism, gene expression and transmitter release. We used optical imaging to explore the spatiotemporal dynamics of Ca(2+) signaling in non-outer segment regions of rods and cones. Sustained depolarization, designed to emulate photoreceptor activation in the darkness, evoked a standing Ca(2+) gradient in tiger salamander photoreceptors with spatially-averaged intracellular Ca(2+) concentration within synaptic terminals of approximately 2 microM and lower (approximately 750 nM) intracellular calcium concentration in the ellipsoid. Measurements from axotomized cell bodies and isolated ellipsoids showed that Ca(2+) enters the two compartments via both local L-type Ca(2+) channels and diffusion. The results from optical imaging studies were supported by immunostaining analysis. L-type voltage-operated Ca(2+) channels and plasma membrane Ca(2+) ATPases were highly expressed in synaptic terminals with progressively lower expression levels in the cell body and ellipsoid. These results show photoreceptor Ca(2+) homeostasis is controlled in a region-specific manner by direct Ca(2+) entry and diffusion as well as Ca(2+) extrusion. Moreover, quantitative measurement of intracellular calcium concentration levels in different photoreceptor compartments indicates that the dynamic range of Ca(2+) signaling in photoreceptors is approximately 40-fold, from approximately 50 nM in the light to approximately 2 microM in darkness.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antimycin A / analogs & derivatives
  • Antimycin A / pharmacology
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels, L-Type / metabolism
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology*
  • Calcium-Transporting ATPases / metabolism
  • Cation Transport Proteins / metabolism
  • Dose-Response Relationship, Drug
  • Drug Interactions
  • Extracellular Space / drug effects
  • Extracellular Space / metabolism*
  • Immunohistochemistry / methods
  • Models, Biological
  • Nifedipine / pharmacology
  • Photoreceptor Cells / cytology*
  • Photoreceptor Cells / metabolism*
  • Plasma Membrane Calcium-Transporting ATPases
  • Potassium / pharmacology
  • Reaction Time / drug effects
  • Retinal Cone Photoreceptor Cells / drug effects
  • Retinal Rod Photoreceptor Cells / drug effects
  • Urodela

Substances

  • Calcium Channel Blockers
  • Calcium Channels, L-Type
  • Cation Transport Proteins
  • antimycin
  • Antimycin A
  • Plasma Membrane Calcium-Transporting ATPases
  • Calcium-Transporting ATPases
  • Nifedipine
  • Potassium
  • Calcium