May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
The effect of partial inhibition of retinal Na/K–ATPase on ERG
Author Affiliations & Notes
  • A.E. Weymouth
    Optometry and Vision Sciences, University of Melbourne, Melbourne, Australia
  • J.A. Phipps
    Optometry and Vision Sciences, University of Melbourne, Melbourne, Australia
  • A.J. Vingrys
    Optometry and Vision Sciences, University of Melbourne, Melbourne, Australia
  • Footnotes
    Commercial Relationships  A.E. Weymouth, None; J.A. Phipps, None; A.J. Vingrys, None.
  • Footnotes
    Support  none
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 1349. doi:
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      A.E. Weymouth, J.A. Phipps, A.J. Vingrys; The effect of partial inhibition of retinal Na/K–ATPase on ERG . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1349.

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

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Abstract

Abstract: : Purpose: Na+/K+–ATPase maintains the photoreceptoral dark current. This study considers retinal function following partial inhibition of Na+/K+–ATPase in rodents. Methods: Deeply anaesthetised (ketamine:xylazine 35:5mg/kg im; proxymetacaine hydrochloride 5mg/mL gt) Sprague–Dawley rats (n=20) were intravitreally injected in one eye (contralateral control) with several concentrations of ouabain (1–0.001mM) to produce varying levels of Na+/K+–ATPase inhibition. Electroretinograms (ERG) were obtained every five minutes for up to two hours after ouabain injection and the rod extracted a–wave was modelled using the known kinetics of phototransduction (RmPIII, Log S). Whole retinae from both eyes were immediately harvested following pentobarbitone sacrifice (60mg/kg ic) and Na+/K+–ATPase activity was quantified by spectrophotometric measurement of phosphate liberation (in presence/absence of ouabain). Some animals were studied over longer time frames (3, 6, 12, 24 hours) to consider the persistence of ouabain binding. Results: Intravitreal ouabain reduced receptoral and postreceptoral function in a dose–dependent manner over a 90 minute interval. At 0.1mM, RmPIII was markedly decreased (–93%) with minor effect on gain (Log S –5%). At 0.01mM, RmPIII was halved with no change to sensitivity. These physiologic findings correlated with the in vitro assays of residual Na+/K+–ATPase activity. The RmPIII showed partial recovery (+3%) 24 hours after injection 0.1mM ouabain. Conclusions: Partial inhibition of Na+/K+–ATPase results in normal gain and decreased RmPIII in a dose–dependent manner. The time course for recovery demonstrates partial dissociation of ouabain from its binding site after 24 hours. These outcomes are fundamental in elucidating those processes that generate the photoreceptoral dark current.

Keywords: NaK ATPase • electroretinography: non–clinical • photoreceptors: visual performance 
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