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

Abstract

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 Ca2+ signalling and contractility of myocytes and pericytes in different sections of microvascular networks in situ have not been investigated. We aimed to investigate Ca2+ signalling and functional responses, in a microcirculatory network in situ. Using live confocal imaging of ureteric microvascular networks, we have studied the architecture, morphology, Ca2+ signalling and contractility of myocytes and pericytes. Ca2+ 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, Ca2+ signals arise from Ca2+ release from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate-induced Ca2+ release and not via ryanodine receptors or Ca2+ 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 Ca2+ signals between arteriolar and venular networks dependent on gap junctions and Ca2+ entry via L-type Ca2+ channels. Endothelial Ca2+ signalling inhibits intracellular Ca2+ oscillations in myocytes and pericytes via L-arginine/nitric oxide pathway and intercellular propagating Ca2+ signals via EDHF. Increases of Ca2+ 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.

A role of the sodium pump in spreading ischemia in rats

“…Endothelium expresses a 2 NaKA as well, but augmented endothelial Ca 2þ signaling should antagonize VSMC and pericyte contraction because endothelial Ca 2þ signaling inhibits VSMC and pericyte Ca 2þ signaling via NO and EDHF. 72 Interestingly, however, ouabain (1-10 mmol/L) was previously reported to antagonize the endothelium-dependent hyperpolarizing effect of vasodilators such as acetylcholine or proteaseactivated receptor 2 ligand on VSMCs of rat and cat MCAs. 73,74 This would favor VSMC depolarization, activation of L-type Ca 2þ channels and contraction.…”

Calcium Signalling in Pericytes

“…Confocal Ca 2+ imaging has brought many advantages to the study of Ca 2+ signalling in situ. Confocal images of vessels permit the visualization of individual vascular smooth muscle cells, pericytes and endothelial cells, and so quantification of changes of Ca 2+ signals in these cells can be made and then correlated with mechanical or electrical events [12,13,14,15,16,17,18]. In this review, we attempt to summarize our results and those of other authors over the last 2 decades in the field of Ca 2+ signalling in pericytes.…”

“…D Images of myocytes (i), precapillary pericytes (ii), capillary pericytes (iii) and postcapillary pericytes (iv) stained with fluorescently labelled phalloidin. Data were reproduced from Borysova et al [15] with permission. …”

“…There is general agreement that precapillary pericytes are contractile cells. They express smooth muscle α-actin (α-SMA) [15,20,27,28,29], tropomyosin [30] and cGMP-dependent protein kinase [31] (fig. 1Dii).…”

“…This topology and morphology has been confirmed by scanning electron microscopy studies of microvessels in different tissues [3,4,23,24,25,26] and recently by live confocal imaging of ureteric microvascular network in situ (fig. 1) [15]. …”