April 2009
Volume 50, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2009
Retinal Microvascular KATP Channels: Redox Regulation, Spermine Modulation and Diabetic Alteration
Author Affiliations & Notes
  • M. Fukumoto
    Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan
  • E. Ishizaki
    Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan
  • D. G. Puro
    Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan
  • Footnotes
    Commercial Relationships  M. Fukumoto, None; E. Ishizaki, None; D.G. Puro, None.
  • Footnotes
    Support  EY12505 and RPB
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 18. doi:https://doi.org/
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      M. Fukumoto, E. Ishizaki, D. G. Puro; Retinal Microvascular KATP Channels: Redox Regulation, Spermine Modulation and Diabetic Alteration. Invest. Ophthalmol. Vis. Sci. 2009;50(13):18. doi: https://doi.org/.

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

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Abstract

Purpose: : We assessed the interrelationships of microvascular redox status, spermine-mediated oxidation and diabetes on the function of KATP channels whose activation in retinal microvessels mediates the hyperpolarizing effects of the vasoactive signals, adenosine and dopamine.

Methods: : Ionic currents were monitored via perforated-patch pipettes sealed onto mural cells located on microvascular complexes freshly isolated from the adult rat retina. Intracellular oxidants were monitored with the dye, carboxy-H2DCFDA. The KATP activator, pinacidil (5µM), was used to induce the KATP current. Rats were made diabetic by streptozotocin.

Results: : In a series of 27 experiments, the pinacidil-induced conductance detected in retinal microvessels was enhanced (p < 0.01) by the chemical oxidant, 5,5'-dithionitrobenzoate (DTNB), and diminished (p < 0.01) by dithiothreitol (DTT), a reductant. Other experiments tested the hypothesis that spermine, a polyamine whose catabolism generates H2O2 and other oxidants, plays a role in regulating KATP channel activity in retinal microvessels. Use of an oxidation-sensitive dye demonstrated that exposure to 5mM spermine increased (p < 0.001, n = 17) the concentration of oxidants in microvascular cells. In other experiments, we observed that spermine increased (p < 0.001, n = 7) the KATP conductance by a mechanism sensitive to the reductant, DTT. Conversely, inhibition of spermine synthesis by DFMO decreased (p < 0.001, n= 5) the KATP current. Because diabetes upregulates spermine in retinal microvessels, we conducted 63 experiments using microvessels from diabetic rats. We found that after 6.6± 0.4 weeks of hyperglycemia, the KATP conductance was increased (p < 0.001) by a mechanism sensitive to DTT (p < 0.001) and DFMO (p < 0.001).

Conclusions: : We conclude that the function of KATP channels in retinal microvessels is potently regulated by a redox mechanism driven by the polyamine, spermine. In addition to the identification of spermine-dependent oxidation as a physiological mechanism regulating the activity of microvascular KATP channels, our results also support the possibility that spermine-dependent oxidation plays a role in causing functional changes in the microvasculature of the diabetic retina.

Keywords: retina • ion channels • diabetes 
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