Retinovascular Physiology and Pathobiology

描述（由申请人提供）：我们的长期目标是阐明视网膜微血管系统在健康和疾病中的功能。这是一个重要的目标，因为视觉功能依赖于微血管有效地满足视网膜神经元的代谢需求。此外，糖尿病视网膜中的微血管功能障碍在视网膜病变的组织学体征之前就被检测到，并且可能导致威胁视力的并发症的发展。 我们提出的研究建立在我们最近的进展，阐明视网膜微血管的功能组织。在此期间，我们提供了第一个表征的电紧张架构和功能地形的视网膜微血管。我们发现，局部诱导的电压变化通过间隙连接途径电紧张性地传输到整个视网膜血管网络的网站。我们的初步研究还表明，功能性电压依赖性钙通道（VDCCs）是不均匀分布在视网膜微血管。也就是说，VDCC活性在毛细血管树的远端部位最小，但在毛细血管的近端部分和毛细血管前小动脉中很强。功能性VDCC的这种地形分布的生理重要性通过我们的观察而突出，即即使许多血管活性信号在位于远端毛细血管部位的壁细胞中诱导显著的电压变化，电压诱导的血管反应仅在视网膜微血管的近端而不是远端部分中检测到。因此，我们的新发现支持了工作假设，即在远端毛细血管部位产生的电压变化被传递到近端位置，在近端位置VDCC可将电压变化转化为壁细胞钙的变化，这改变了壁细胞的收缩张力，从而改变了管腔直径。 对于阐明糖尿病如何破坏微血管功能具有潜在的重要性，我们的初步研究表明，VDCC活性在糖尿病视网膜的微血管中减弱。考虑到糖尿病导致视网膜中的氧化应激，我们的初步研究表明，氧化剂抑制非糖尿病视网膜微血管中的VDCC，还原剂恢复糖尿病微血管中的VDCC活性。 为了评估我们关于视网膜微血管生理学和病理学的新想法，我们提出的研究的具体目标将检验以下假设：（1）涉及氧化的机制有助于抑制糖尿病视网膜中的微血管VDCC，以及（2）糖尿病破坏了在远端毛细血管部位产生的电压变化被转换成近端位置的血管反应的机制，视网膜微血管 从长远来看，阐明糖尿病破坏视网膜微血管系统对局部血管活性信号反应能力的机制应有助于制定新的策略来改善并有望预防这种疾病的视力威胁并发症。

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.