April 2011
Volume 52, Issue 14
ARVO Annual Meeting Abstract  |   April 2011
Extensive Modulation of R* but Not PDE* Lifetime by Light in Mouse Rods when Registered in the Intact Retina
Author Affiliations & Notes
  • Frans Vinberg
    BECS, Aalto University, Espoo, Finland
  • Hanna Heikkinen
    BECS, Aalto University, Espoo, Finland
  • Ari Koskelainen
    BECS, Aalto University, Espoo, Finland
  • Footnotes
    Commercial Relationships  Frans Vinberg, None; Hanna Heikkinen, None; Ari Koskelainen, None
  • Footnotes
    Support  Academy of Finland, grant 111866
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 6575. doi:
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      Frans Vinberg, Hanna Heikkinen, Ari Koskelainen; Extensive Modulation of R* but Not PDE* Lifetime by Light in Mouse Rods when Registered in the Intact Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6575.

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

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Purpose: : The average lifetime of PDE* (τE) in mouse rods is believed to be ~0.2 s and the R* lifetime (τR) is thought to be very short (< 50 ms). Light-mediated decline in [Ca2+]i shortens τR through recoverin, but Ca2+ dependent mechanisms of τE modulation have not been identified. Recent data (Woodruff et al. (2008), J. Neurosci. 28:2064-74), however, suggests that also τE is shortened by background light. We studied the modulation of τR and τE (assuming τD = τE) by light in the intact mouse retina with ex vivo ERG.

Methods: : Transretinal ERG was recorded from isolated mouse retinas at 37oC. The retinas were perfused at the photoreceptor side with bicarbonate buffered Ames medium or modified Ringer’s supplemented with L-15. The photoreceptor component was isolated with 20 -50 µM DL-AP4 and 50 - 100 µM BaCl2. The dominant time constant (τD) was determined from saturated rod flash photoresponses (100 - 3000 R*) in darkness and during steps of light (400 R*s-1). Modulation of τR by light was investigated with the "step/flash" protocol (Fain et al. (1989), J. Physiol. 416:215-43).

Results: : τD was 180 ± 6 ms (n = 15) in darkness and 173 ± 12 ms (n = 7) in light-adapted rods. In the seven experiments where τD was determined both in darkness and during steps of light no significant change of τD was observed during light-adaptation. In the step/flash paradigm (4 retinas) the flash responses showed always a clear shortening of saturation time with increasing step intensity Istep. The saturation time of the rod responses to a constant intensity flash decreased as a linear function of Ln(Istep) within the intensity window 80-600 R*s-1 with a slope kΔT = 59 ± 7 ms.

Conclusions: : The τD of mouse rods can be robustly determined with ex vivo ERG from the intact retina, and it is similar to the value determined from single dark-adapted rods by suction electrode recordings. τD was not shortened by backgrounds suppressing up to 70% of the rod saturated response amplitude, indicating that the rate-limiting step of saturated rod photoresponse recovery is not modulated by light. Assuming that τD = τE, the slope kΔT obtained in the step-flash -experiments would correspond to ~30% shortening of τR per e-fold increase in step intensity (Eq. (10) in Nikonov et al. (2000), J. Gen. Physiol. 116:795-824).

Keywords: photoreceptors • electrophysiology: non-clinical • signal transduction 

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