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如何发挥作用。这是一个重要的目标，因为视觉功能取决于微血管能否有效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早在视网膜病变的组织学症状之前就被检测到，并且可能导致威胁视力的并发症的发生。 我们提出的研究建立在我们最近在阐明视网膜微血管系统功能组织方面取得的进展的基础上。在此授权期间，我们首次提供了视网膜微血管的电紧张结构和功能形貌的表征。我们发现局部感应电压变化通过间隙连接通路以电方式传输到整个视网膜血管网络的各个部位。我们的初步研究还表明，功能性电压依赖性钙通道（VDCC）在视网膜微血管内分布不均匀。即，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。我们的观察强调了功能性 VDCC 的这种拓扑分布的生理重要性，即尽管大量血管活性信号引起位于远端毛细血管部位的壁细胞的显着电压变化，但电压诱导的血管舒缩反应仅在视网膜微脉管系统的近端部分而不是远端部分检测到。因此，我们的新发现支持这样的工作假设：远端毛细血管部位产生的电压变化被传输到近端位置，在这些位置，VDCC 可将电压变化转换为壁细胞钙的变化，从而改变壁细胞的收缩张力，从而改变管腔直径。 我们的初步研究表明，糖尿病视网膜微血管中的 VDCC 活性减弱，这对于阐明糖尿病如何破坏微血管功能具有潜在的重要性。更有趣的是，考虑到糖尿病会引起视网膜氧化应激，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，而还原剂可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系统生理学和病理学的新想法，我们提出的研究的具体目标将测试以下假设：（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；（2）糖尿病破坏了将远端毛细血管部位产生的电压变化转换为视网膜微血管系统近端位置的血管舒缩反应的机制。 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作出反应的能力的机制应该有助于制定新的策略来改善并有望预防这种疾病的威胁视力的并发症。

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.