How calcium signals in myocytes and pericytes are integrated across in situ microvascular networks and control microvascular tone()

The microcirculation is the site of gas and nutrient exchange. Control of central or local signals acting on the myocytes, pericytes and endothelial cells within it, is essential for health. Due to technical problems of accessibility, the mechanisms controlling Ca(2+) signalling and contractility of myocytes and pericytes in different sections of microvascular networks in situ have not been investigated. We aimed to investigate Ca(2+) signalling and functional responses, in a microcirculatory network in situ. Using live confocal imaging of ureteric microvascular networks, we have studied the architecture, morphology, Ca(2+) signalling and contractility of myocytes and pericytes. Ca(2+) signals vary between distributing arcade and downstream transverse and precapillary arterioles, are modified by agonists, with sympathetic agonists being ineffective beyond transverse arterioles. In myocytes and pericytes, Ca(2+) signals arise from Ca(2+) release from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate-induced Ca(2+) release and not via ryanodine receptors or Ca(2+) entry into the cell. The responses in pericytes are less oscillatory, slower and longer-lasting than those in myocytes. Myocytes and pericytes are electrically coupled, transmitting Ca(2+) signals between arteriolar and venular networks dependent on gap junctions and Ca(2+) entry via L-type Ca(2+) channels. Endothelial Ca(2+) signalling inhibits intracellular Ca(2+) oscillations in myocytes and pericytes via L-arginine/nitric oxide pathway and intercellular propagating Ca(2+) signals via EDHF. Increases of Ca(2+) in pericytes and myocytes constrict all vessels except capillaries. These data reveal the structural and signalling specializations allowing blood flow to be regulated by myocytes and pericytes.