Retinovascular Physiology and Pathobiology

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DESCRIPTION (provided by applicant): Our long-range objective is to elucidate how the retinal microvasculature functions in health and disease. This is an important goal because visual function depends upon microvessels effectively meeting the metabolic needs of retinal neurons. In addition, microvascular dysfunction in the diabetic retina is detected well before histological signs of retinopathy and may contribute to the development of sight-threatening complications. Our proposed studies build upon our recent progress in elucidating the functional organization of the retinal microvasculature. During this granting period, we provided the first characterization of the electrotonic architecture and the functional topography of retinal microvessels. We found that a locally induced voltage change is transmitted electrotonically via gap junction pathways to sites throughout a retinal vascular network. Our preliminary studies also indicate that functional voltage-dependent calcium channels (VDCCs) are heterogeneously distributed within the retinal microvasculature. Namely, VDCC activity is minimal at distal sites in the capillary tree, but is robust in the proximal portion of capillaries and in the pre-capillary arterioles. The physiological importance of this topographical distribution of functional VDCCs is highlighted by our observation that even though numerous vasoactive signals induce significant voltage changes in the mural cells located at distal capillary sites, voltage-induced vasomotor responses are detected only in the proximal, not the distal, portion of the retinal microvasculature. Thus, our new findings support the working hypothesis that voltage changes generated at distal capillary sites are transmitted to proximal locations where VDCCs are available to transduce a change in voltage into a change in mural cell calcium, which alters the contractile tone of mural cells and thereby, alters the lumen diameter. Of potential importance for clarifying how diabetes disrupts microvascular function, our preliminary studies indicate that VDCC activity becomes attenuated in microvessels of the diabetic retina. Of further interest given that diabetes causes oxidative stress in the retina, our preliminary studies indicate that oxidants inhibit VDCCs in non-diabetic retinal microvessels and that reductants restore VDCC activity in diabetic microvessels. To evaluate our new ideas concerning the physiology and pathobiology of the retinal microvasculature, the specific aims of our proposed studies will test the hypotheses that (1) a mechanism involving oxidation contributes to the inhibition of microvascular VDCCs in the diabetic retina and (2) diabetes disrupts the mechanism by which a voltage change generated at distal capillary sites is transduced into a vasomotor response at proximal locations in the retinal microvasculature. Over the long-term, elucidating mechanisms by which diabetes disrupts the ability of the retinal microvasculature to respond to local vasoactive signals should aid in devising new strategies to ameliorate and hopefully, prevent sight-threatening complications of this disease.