Endothelial signaling and the dynamic regulation of arterial tone: A surreptitious relationship

Distribution and relative expression of vasoactive receptors on arteries

Arterial tone is regulated by multiple ligand-receptor interactions, and its dysregulation is involved in ischemic conditions such as acute coronary spasm or syndrome. Understanding the distribution of vasoactive receptors on different arteries may help guide the development of tissue-specific vasoactive treatments against arterial dysfunction. Tissues were harvested from coronary, mesenteric, pulmonary, renal and peripheral human artery (n = 6 samples of each) and examined using a human antibody array to determine the expression of 29 vasoactive receptors and 3 endothelin ligands. Across all types of arteries, outer diameter ranged from 2.24 ± 0.63 to 3.65 ± 0.40 mm, and AVPR1A was the most abundant receptor. The expression level of AVPR1A in pulmonary artery was similar to that in renal artery, 2.2 times that in mesenteric artery, 1.9 times that in peripheral artery, and 2.2 times that in coronary artery. Endothelin-1 was expressed at significantly higher levels in pulmonary artery than peripheral artery (8.8 times), mesenteric artery (5.3 times), renal artery (7.9 times), and coronary artery (2.4 times). Expression of ADRA2B was significantly higher in coronary artery than peripheral artery. Immunohistochemistry revealed abundant ADRA2B in coronary artery, especially vessels with diameters below 50 μm, but not in myocardium. ADRA2C, in contrast, was expressed in both myocardium and blood vessels. The high expression of ADRA2B in coronary artery but not myocardium highlights the need to further characterize its function. Our results help establish the distribution and relative levels of tone-related receptors in different types of arteries, which may guide artery-specific treatments.

Precapillary sphincters maintain perfusion in the cerebral cortex

Active nerve cells release vasodilators that increase their energy supply by dilating local blood vessels, a mechanism termed neurovascular coupling and the basis of BOLD functional neuroimaging signals. Here, we reveal a mechanism for cerebral blood flow control, a precapillary sphincter at the transition between the penetrating arteriole and first order capillary, linking blood flow in capillaries to the arteriolar inflow. The sphincters are encircled by contractile mural cells, which are capable of bidirectional control of the length and width of the enclosed vessel segment. The hemodynamic consequence is that precapillary sphincters can generate the largest changes in the cerebrovascular flow resistance of all brain vessel segments, thereby controlling capillary flow while protecting the downstream capillary bed and brain tissue from adverse pressure fluctuations. Cortical spreading depolarization constricts sphincters and causes vascular trapping of blood cells. Thus, precapillary sphincters are bottlenecks for brain capillary blood flow.

Precapillary sphincters are mural cells encircling an indentation of blood vessels where capillaries branch off from penetrating arterioles (PAs), but their existence and role in the brain is not fully understood. Here authors describe these structures at PAs in the cortex and show that they constrict during cortical spreading depolarization in mice.