Brief communication

Release of immunoreactive endothelin from the heart during percutaneous transluminal coronary angioplasty☆

Ischemia and Reperfusion (I/R) injuries are associated with coronary artery hypercontracture. They are mainly originated by an exacerbated response to agonists released by endothelium such as Endothelin (ET-1), involving the alteration in intracellular calcium handling. Recent evidences have highlighted the implication of Store-Operated Calcium Channels (SOCC) in intracellular calcium homeostasis in coronary artery. However, little is known about the role of SOCC in the regulation of coronary vascular tone under I/R.

The aim of this study was to evaluate the role of SOCC and l-type Ca²⁺ channels (LTCC) in coronary artery vasoconstriction originated by ET-1 in I/R. We used Left Anterior Descendent coronary artery (LAD) rings, isolated from Wistar rats, to study the contractility and intracellular Ca²⁺ concentration ([Ca²⁺]_i) under a simulated I/R protocol. We observed that responses to high-KCL induced depolarization and caffeine-induced Ca²⁺ release are attenuated in coronary artery under I/R. Furthermore, ET-1 addition in ischemia promotes transient and small rise of [Ca²⁺]_i and coronary vascular tone. Meanwhile, these effects are significantly potentiated during reperfusion. The resulting ET-1-induced vasoconstrictions and [Ca²⁺]_i increase were abolished by; GSK-7975A and gadolinium, inhibitors of SOCC; and nifedipine a widely used inhibitor of LTCC. Interestingly, using in situ Proximity Ligation Assay (PLA) in isolated coronary smooth muscle cells we found significant colocalization of LTCC Ca_V1.2 isoform with Orai1, the pore forming subunit of SOCC, and TRPC1 under I/R.

Our data suggest that hypercontraction of coronary artery induced by ET-1 after I/R involves the co-activation of LTCC and SOCC, which colocalize significantly in the sarcolemma of coronary smooth muscle cells.

Endothelin (ET)-1 derived from endothelial cells has a much more important role in cardiovascular system regulation than the ET-2 and ET-3 isoforms. Numerous lines of evidence indicate that ET-1 possesses a number of biological activities leading to cardiovascular diseases (CVD) including hypertension and atherosclerosis. Physiological and pathophysiological responses to ET-1 in various tissues are mediated by interactions with ET_A- and ET_B-receptor subtypes. Both subtypes on vascular smooth muscle cells mediate vasoconstriction, whereas the ET_B-receptor subtype on endothelial cells contributes to vasodilatation and ET-1 clearance. Although selective ET_A- or nonselective ET_A/ET_B-receptor antagonisms have been assumed as potential strategies for the treatment of several CVD based on clinical and animal experiments, it remains unclear which antagonisms are suitable for individuals with CVD because upregulation of the nitric oxide system via the ET_B receptor is responsible for vasoprotective effects such as vasodilatation and anti-cell proliferation. In this review, we have summarized the current understanding regarding the role of ET receptors, especially the ET_B receptor, in CVD.

Endothelin-1 and norepinephrine are involved in myocardial ischemia/reperfusion injury. The aim of this study was to investigate the role of endogenously generated endothelin-1 in ischemia/reperfusion-induced norepinephrine overflow and cardiac dysfunction using a nonselective prototype of endothelin-converting enzyme (ECE) inhibitor, phosphoramidon, and a selective ECE inhibitor, SM-19712 (4-chloro-N-[[(4-cyano-3-methyl-1-phenyl-1H-pyrazol-5-yl)amino]carbonyl]benzenesulfonamide, monosodium salt). According to the Langendorff technique, isolated Sprague–Dawley rat hearts were subjected to 40-min global ischemia followed by 30-min reperfusion. Phosphoramidon and SM-19712 were perfused 30 min before ischemia and during reperfusion. Endothelin-1 level in left ventricle was increased by ischemia/reperfusion. This increase in left ventricular endothelin-1 level was suppressed by treatment with SM-19712. SM-19712 significantly improved ischemia/reperfusion-induced cardiac dysfunction such as decreased left ventricular developed pressure and dP/dt_max and increased left ventricular end diastolic pressure. In addition, this agent suppressed excessive norepinephrine overflow in the coronary effluent from the post-ischemic heart. In contrast, treatment with phosphoramidon further enhanced left ventricular endothelin-1 level and norepinephrine overflow, and significantly worsened cardiac dysfunction after ischemia/reperfusion. These responses such as exaggerated norepinephrine overflow and the cardiac dysfunction observed after ischemia/reperfusion were markedly suppressed in the presence of a selective endothelin ET_A receptor antagonist, ABT-627 [2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid]. These findings indicate that cardiac endothelin-1 production is enhanced by ischemia/reperfusion, and this endogenously increased endothelin-1 is involved in post-ischemic norepinephrine overflow and cardiac dysfunction via the activation of endothelin ET_A receptors.

Increases in the levels of plasma endothelins (ETs) have been reported after percutaneous transluminal coronary angioplasty (PTCA). To examine the mechanism of this increase, we measured plasma endothelin-1 (ET-1) and thrombomodulin (TM) levels in both the Valsalva sinus (VAL) and the great cardiac vein (GCV) together with oxygen saturation of the GCV (Sat.GCVO₂) during right atrial pacing and PTCA. Thirty patients with stenoses in the left anterior descending coronary arteries were enrolled. A fiberoptic pulmonary artery catheter was placed in GCV for monitoring Sat.GCVO₂, and blood sampling was repeated before and after each procedure. ET-1 did not increase during pacing, but after PTCA it significantly increased from basal levels to 24.4±8.3 pg/ml in GCV (P<0.01) and 19.3±7.4 in VAL (P<0.05). Basal TM levels in GCV and VAL were significantly higher in diabetic than in non-diabetic patients, but TM did not change during pacing and PTCA. Sat.GCVO₂ significantly decreased from the basal level during pacing and PTCA. We speculate that direct endothelial cell damage is more responsible for the increase of ET-1 during PTCA than myocardial ischemia. Our data indicate that ET-1 may be a useful marker for acute endothelial damage, while TM reflects only chronic and general damage of endothelial cells.