Figure 1.

Functional overlapping mechanism from the luminal (endothelium) and abluminal side of a parenchymal arteriole. In addition to direct neuronal-vessel interactions vascular smooth muscle cells (VSMC) are tonically influenced by agonists and/or mechanically activated pathways from the endothelium and from signals released by astrocytic processes also in direct contact with the vessels. The presence of polarized and discrete ion channel types in the layer formed by endothelial cells and astrocytes, provides functional further support for bi-directional communication between these cells and VSMC, as well as, for an electrotonic arrangement capable of modulating vascular tone and conduction of signals over long distances along the microvessel. VDCC (voltage-dependent Ca²⁺ channels), TRPV4 (transient receptor potential vanilloid), BK (Ca²⁺-activated voltage-dependent K⁺ channel), IK (intermediate conductance Ca²⁺ activated K⁺ channel), SK (small conductance Ca²⁺ activated K⁺ channel), and K_ir (inwardly rectifying K⁺ channel).