Perivascular tissue inhibits rho‐kinase‐dependent smooth muscle Ca²⁺ sensitivity and endothelium‐dependent H₂S signalling in rat coronary arteries

Abstract

Key pointsr Local regulation of vascular resistance adjusts coronary blood flow to metabolic demand, although the mechanisms involved are not comprehensively understood r We show that heart tissue surrounding rat coronary arteries releases diffusible factors that regulate vasoconstriction and relaxation r Perivascular tissue reduces rho-kinase-dependent smooth muscle Ca 2+ sensitivity and constriction of coronary arteries to serotonin, the thromboxane analogue U46619 and the α 1 -adrenergic agonist phenylephrine r Endothelium-dependent relaxation of coronary arteries in response to cholinergic stimulation is inhibited by perivascular tissue as a result of reduced endothelial Ca 2+ responses and attenuated H 2 S-dependent signalling r These results establish cellular mechanisms by which perivascular heart tissue can modify local vascular tone and coronary blood flow Abstract Interactions between perivascular tissue (PVT) and the vascular wall modify artery tone and contribute to local blood flow regulation. Using isometric myography, fluorescence microscopy, membrane potential recordings and phosphospecific immunoblotting, we investigated the cellular mechanisms by which PVT affects constriction and relaxation of rat coronary septal arteries. PVT inhibited vasoconstriction to thromboxane, serotonin and α 1 -adrenergic stimulation but not to depolarization with elevated extracellular [K + ]. When PVT was wrapped around isolated arteries or placed at the bottom of the myograph chamber, a smaller yet significant inhibition of vasoconstriction was observed. Resting membrane potential, depolarization to serotonin or thromboxane stimulation, and resting and serotonin-stimulated vascular smooth muscle [Ca 2+ ]-levels were unaffected by PVT. Serotonin-induced vasoconstriction was almost abolished by rho-kinase inhibitor Y-27632 and modestly reduced by protein kinase C inhibitor bisindolylmaleimide X. PVT reduced phosphorylation of myosin phosphatase targeting subunit (MYPT) at Thr850 by ß40% in serotonin-stimulated arteries but had no effect on MYPT-phosphorylation in arteries depolarized with elevated extracellular [K + ]. The net anti-contractile effect of PVT was accentuated after endothelial denudation. PVT also impaired vasorelaxation and endothelial Ca 2+ responses to cholinergic stimulation. Methacholine-induced vasorelaxation was mediated by NO and H 2 S, and particularly the H 2 S-dependent (DL-propargylglycine-and XE991-sensitive) component was attenuated by PVT. Vasorelaxation to NO-and H 2 S-donors was maintained in arteries with PVT. In conclusion, cardiomyocyte-rich PVT surrounding coronary arteries releases diffusible factors that reduce rho-kinase-dependent smooth muscle Ca 2+ sensitivity and endothelial Ca 2+ responses. These mechanisms inhibit agonist-induced vasoconstriction and endothelium-dependent vasorelaxation and suggest new signalling pathways for metabolic regulation of blood flow.

Coronary artery hypoxic vasorelaxation is augmented by perivascular adipose tissue through a mechanism involving hydrogen sulphide and cystathionine‐β‐synthase

“…In arteries with PVAT intact, the attenuated contraction was, interestingly, unaffected by inhibitors of CSE (PPG), CBS (AOAA) or of the MPST pathway (aspartate), applied alone or in combination ( Figure 3B). 19,20 We found no anticontractile effect of myocardium on responses to U46619 under normoxic conditions, suggesting that there is no ongoing basal release of anticontractile factors from myocardium adjacent to the porcine coronary artery. Evaluation of its identity needs further experimentation, and there are a number of possible candidates.…”

“…[6][7][8][9][10][11][12] In rat coronary arteries, cardiomyocyte-rich perivascular tissue had an anticontractile effect on agonist-induced contractions, which involved a reduction in Ca 2+ sensitivity and was unaffected by the CSE inhibitor PPG. 19,20 We found no anticontractile effect of myocardium on responses to U46619 under normoxic conditions, suggesting that there is no ongoing basal release of anticontractile factors from myocardium adjacent to the porcine coronary artery. This is in contrast to PVAT and endothelium, the presence of both of which was associated with an anticontractile effect as evidenced by the requirement of a lower concentration of U46619 to induce contractile tone.…”

Pro‐contractile effects of perivascular fat in health and disease

“…The coexistence of pro‐contractile and anti‐contractile actions of PVAT may seem contradictory, but such dual effects have also been demonstrated in the same arteries and within the same studies (Soltis and Cassis, ; Lohn et al , ; Ketonen et al , ; Li et al , ; Aalbaek et al , ). Indeed, some of the PVAT‐derived factors such as leptin, TNF‐α, IL‐6 and hydrogen peroxide are known to have both contractile and relaxant properties (Brian and Faraci, ; Orshal and Khalil, ; Thakali et al , ; Virdis et al ., ).…”

“…Accumulating evidence suggests that the anti‐contractile effect of PVAT relies on smooth muscle K + channels, specifically the activation of voltage‐gated K + channels (K V 7) and Ca 2+ ‐activated K + channels (BK Ca ) through endothelium‐independent and ‐dependent pathways respectively. Interestingly, in healthy rat coronary septal arteries, increases in PVAT also reduce Rho kinase‐dependent Ca 2+ sensitivity in vascular smooth muscle (Aalbaek et al ., ). This contrasts with the observation that PVAT from pig coronary artery enhances vasocontraction via Rho kinase (Owen et al , ).…”

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

“…[80]. In addition, the role of PAT-derived H 2 S may be species-specific and vary between different vascular beds, as CSE expression is much lower in mice PAT than in rat [81, 82]. …”