Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
J Physiol. 2011 May 1;589(Pt 9):2383-99. doi: 10.1113/jphysiol.2010.202937. Epub 2011 Mar 8.
The capillary/arteriole complex is the key operational unit regulating local perfusion to meet metabolic demand. However, much remains to be learned about how this multi cellular unit is functionally organized. To help address this challenge, we characterized the electrotonic architecture of the retinal microvasculature, which is particularly well adapted for the decentralized control of blood flow. In this study, we quantified the transmission of voltage between pairs of perforated-patch pipettes sealed onto abluminal cells located on microvascular complexes freshly isolated from the adult rat retina. These complexes consisted of capillaries,as well as tertiary and secondary arterioles. Dual recording experiments revealed that voltage spreading axially through a capillary, tertiary arteriole or secondary arteriole is transmitted very efficiently with a decay rate of only ∼5% per 100 μm. However, the retinal microvasculature is not simply a well-coupled syncytium since we detected significant voltage dissipation with radial abluminal cell-to-endothelium transmission and also at branch points between a capillary and its tertiary arteriole and between tertiary and secondary arterioles. Consistent with capillaries being particularly well-suited for the task of transmitting voltages induced by vasoactive signals, radial transmission is most efficient in this portion of the retinal microvasculature. Dual recordings also revealed that angiotensin II potently inhibits axial transmission. As a functional consequence, the geographical extent of the microvasculature's response to voltage-changing inputs is markedly restricted in the presence of angiotensin. In addition, this effect of angiotensin established that the electrotonic architecture of the retinal microvasculature is not static, but rather, is dynamically modulated by vasoactive signals.
毛细血管/小动脉复合体是调节局部灌注以满足代谢需求的关键功能单位。然而，对于这个多细胞单位如何进行功能组织，仍有许多需要了解。为了帮助解决这一挑战，我们对视网膜微血管的电紧张结构进行了特征描述，这种结构特别适合于对血流的分散控制。在这项研究中，我们量化了用穿孔贴片封接在刚从成年大鼠视网膜中分离的微血管复合体的基膜细胞上的一对穿孔贴片之间的电压传递。这些复合体包括毛细血管以及三级和二级小动脉。双记录实验表明，电压通过毛细血管、三级小动脉或二级小动脉轴向传播的效率非常高，衰减率仅为每 100μm 约 5%。然而，视网膜微血管并不是一个简单的紧密偶联的合胞体，因为我们检测到径向基膜细胞-内皮细胞之间的电压耗散，以及在毛细血管与其三级小动脉以及三级和二级小动脉之间的分支点处也存在电压耗散。由于毛细血管特别适合传递血管活性信号诱导的电压，因此在视网膜微血管的这一部分，径向传输的效率最高。双记录还表明，血管紧张素 II 强烈抑制轴向传输。作为一个功能结果，血管紧张素存在时，电压变化输入对微血管的地理范围的反应明显受到限制。此外，血管紧张素的这种作用表明，视网膜微血管的电紧张结构不是静态的，而是可以被血管活性信号动态调节。
