May 2007
Volume 48, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2007
Distribution and Roles of Mitochondria, Endoplasmic Reticulum and Ca2+ Transporters in Mouse Rod and Cone Photoreceptor Synapses
Author Affiliations & Notes
  • J. E. Johnson, Jr.
    University of Houston-Downtown, Houston, Texas
  • G. A. Perkins
    University of California: San Diego, San Diego, California
  • A. Giddabasappa CS
    University of Houston, Houston, Texas
  • S. Chaney
    University of Houston, Houston, Texas
  • W. Xiao
    University of Houston, Houston, Texas
  • A. White
    University of California: San Diego, San Diego, California
  • J. Brown
    University of California: San Diego, San Diego, California
  • J. Waggoner
    University of California: San Diego, San Diego, California
  • M. H. Ellisman
    University of California: San Diego, San Diego, California
  • D. A. Fox
    University of Houston, Houston, Texas
  • Footnotes
    Commercial Relationships J.E. Johnson, None; G.A. Perkins, None; A. Giddabasappa CS, None; S. Chaney, None; W. Xiao, None; A. White, None; J. Brown, None; J. Waggoner, None; M.H. Ellisman, None; D.A. Fox, None.
  • Footnotes
    Support NIH Grants ES012482, EY07024, EY07088, RR04050 and NS14718.
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 3063. doi:
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      J. E. Johnson, Jr., G. A. Perkins, A. Giddabasappa CS, S. Chaney, W. Xiao, A. White, J. Brown, J. Waggoner, M. H. Ellisman, D. A. Fox; Distribution and Roles of Mitochondria, Endoplasmic Reticulum and Ca2+ Transporters in Mouse Rod and Cone Photoreceptor Synapses. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3063.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose:: The kinetic differences between rod and cone exocytosis/endocytosis likely results from differences in metabolic coupling and cross-talk between presynaptic photoreceptor mitochondria and endoplasmic reticulum, and the differential use of the plasma membrane Ca2+-ATPase (PMCA) and Na+-Ca2+ exchanger (NCX). The present study identified the mechanisms of ATP and Ca2+ dynamics at rod and cone ribbon synapses.

Methods:: Central retinal tissue from adult C57BL/6 mice was used. Immunocytochemical and high-resolution confocal microscopy experiments used fixed-frozen vertical sections. Primary antibodies were selected for their tissue/cellular specificity and ability to recognize single/multiple protein isoforms or all splice variants of selected isoforms. Electron microscopy and 3-D electron tomography studies used our standard procedures.

Results:: Immunocytochemical and confocal studies showed distinct retinal lamination patterns and distribution of mitochondria, endoplasmic reticulum, pan-PMCA and NCX1 in photoreceptor synapses. Rod spherule membranes uniformly and intensely stained for PMCA, whereas the larger cone pedicles preferentially stained for NCX1 at their active zones and PMCA near their mitochondria. Endoplasmic reticulum networks were larger and denser in cone pedicles. Electron microscopy and electron tomography revealed that the number, location, size, volume, cristae surface area and crista junction diameter of mitochondria differed in spherules and pedicles. Pedicles had ~5 medium-sized mitochondria clustered far from active zones, whereas spherules had one large mitochondria near the active zone.

Conclusions:: These results indicate that ATP demand and mitochondria ATP production are greater in pedicles than spherules. Mitochondria in rod spherules, in contrast to cone pedicles, likely buffer local Ca2+ microdomains. Pedicles utilize low affinity/high turnover NCX to rapidly lower their high [Ca2+], whereas spherules employ high affinity/low turnover PMCA and their mitochondria to maintain low [Ca2+] and increase their sensitivity and signal-to-noise ratio. These studies reveal that several integrated cellular and subcellular components interact and contribute to the differential production of ATP and regulation of Ca2+ homeostasis/dynamics in rod and cone synaptic terminals.

Keywords: photoreceptors • synapse • calcium 
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