Coronary Artery Contractility Research Articles

Contribution of calcium dysregulation to impaired coronary artery contraction in Zucker diabetic fatty rats.

Diabetic coronary artery injury is closely associated with Ca2+ dysregulation, although the underlying mechanism remains unclear. This study explored the role and mechanism of Ca2+ handling in coronary artery dysfunction in type 2 diabetic rats. Zucker diabetic fatty (ZDF) rats were used as the type 2 diabetes mellitus model. The contractility of coronary artery rings induced by KCl, CaCl2 , 5-HT and U46619 was significantly lower in ZDF rats than in Zucker lean rats. Vasoconstriction induced by 5-HT and U46619 was greatly inhibited by nifedipine. However, in the presence of 1μM nifedipine or in the Ca2+ -free KH solution containing 1μM nifedipine, there was no difference in the vasoconstriction between Zucker lean and ZDF rats. Store-operated calcium channels (SOCs) were not involved in coronary vasoconstriction. The downregulation of contractile proteins and the upregulation of synthesized proteins were in coronary artery smooth muscle cells (CASMCs) from ZDF rats. Metformin reversed the reduction of vasoconstriction in ZDF rats. Taken together, L-type calcium channel is important for regulating the excitation-contraction coupling of VSMCs in coronary arteries, and dysregulation of this channel contributes to the decreased contractility of coronary arteries in T2DM.

C63. Myocardial bridging on coronary angiography: an innocent bystander or a culprit in myocardial infarction?

Abstract Myocardial bridging is one of the nonatherosclerotic causes of coronary artery disease and is characterized by muscles overlying the intramyocardial course of a major epicardial coronary artery segment, leading to systolic compression. This condition is usually benign but can be associated with unstable angina, myocardial infarction, and death. We report herein a myocardial infarction associated with a subtotal systolic narrowing of the LAD by a myocardial bridge. A 57-year-old-man with chronic heart failure caused by myocardial bridging post-non-ST elevation myocardial infarction and hypertensive heart disease. The electrocardiography showed sinus rhythm, echocardiography shows normal left and right ventricular function, regional wall motion abnormality, grade I diastolic dysfunction and “milking effect” was observed in the mid-segment of the left anterior descending coronary artery on the coronary angiogram. Schwarz type C is categorized in this case, β-blockers and calcium channel blockers remain the mainstay of treatment and relieve hemodynamic disorders caused by myocardial bridging by decreasing heart rate, increasing the period of diastolic coronary filling, and decreasing coronary artery contractility and compression. Other diagnostic modalities needed if symptoms persist despite optimal medical therapy and myotomy, coronary artery bypass graft, or stent implantation can be considered in these patients. At the six-month follow-up visit, the patient had no acute coronary syndrome event, but chest pain and heart failure were felt occasionally.

C63. Myocardial bridging on coronary angiography: an innocent bystander or a culprit in myocardial infarction?

Abstract Myocardial bridging is one of the nonatherosclerotic causes of coronary artery disease and is characterized by muscles overlying the intramyocardial course of a major epicardial coronary artery segment, leading to systolic compression. This condition is usually benign but can be associated with unstable angina, myocardial infarction, and death. We report herein a myocardial infarction associated with a subtotal systolic narrowing of the LAD by a myocardial bridge. A 57-year-old-man with chronic heart failure caused by myocardial bridging post-non-ST elevation myocardial infarction and hypertensive heart disease. The electrocardiography showed sinus rhythm, echocardiography shows normal left and right ventricular function, regional wall motion abnormality, grade I diastolic dysfunction and “milking effect” was observed in the mid-segment of the left anterior descending coronary artery on the coronary angiogram. Schwarz type C is categorized in this case, β-blockers and calcium channel blockers remain the mainstay of treatment and relieve hemodynamic disorders caused by myocardial bridging by decreasing heart rate, increasing the period of diastolic coronary filling, and decreasing coronary artery contractility and compression. Other diagnostic modalities needed if symptoms persist despite optimal medical therapy and myotomy, coronary artery bypass graft, or stent implantation can be considered in these patients. At the six-month follow-up visit, the patient had no acute coronary syndrome event, but chest pain and heart failure were felt occasionally.

TMEM16A is implicated in the regulation of coronary flow and is altered in hypertension

Coronary artery disease leads to ischaemic heart disease and ultimately myocardial infarction. Thus, it is important to determine the factors that regulate coronary blood flow. Ca2+ -activated chloride channels contribute to the regulation of arterial tone; however, their role in coronary arteries is unknown. The aim of this study was to investigate the expression and function of the main molecular correlate of Ca2+ -activated chloride channels, TMEM16A, in rat coronary arteries. We performed mRNA and protein analysis, electrophysiological studies of coronary artery myocytes, and functional studies of coronary artery contractility and coronary perfusion, using novel inhibitors of TMEM16A. Furthermore, we assessed whether any changes in expression and function occurred in coronary arteries from spontaneously hypertensive rats (SHRs). TMEM16A was expressed in rat coronary arteries. The TMEM16A-specific inhibitor, MONNA, hyperpolarised the membrane potential in U46619. MONNA, T16Ainh -A01, and Ani9 attenuated 5-HT/U46619-induced contractions. MONNA and T16Ainh -A01 also increased coronary flow in Langendorff perfused rat heart preparations. TMEM16A mRNA was increased in coronary artery smooth muscle cells from SHRs, and U46619 and 5-HT were more potent in arteries from SHRs than in those from normal Wistar rats. MONNA diminished this increased sensitivity to U46619 and 5-HT. In conclusion, TMEM16A is a key regulator of coronary blood flow and is implicated in the altered contractility of coronary arteries from SHRs.

Proteinase-activated receptors 1 and 2 and the regulation of porcine coronary artery contractility: a role for distinct tyrosine kinase pathways

Because angiotensin-II-mediated porcine coronary artery (PCA) vasoconstriction is blocked by protein tyrosine kinase (PYK) inhibitors, we hypothesized that proteinase-activated receptors (PARs), known to regulate vascular tension, like angiotensin-II, would also cause PCA contractions via PYK-dependent signalling pathways. Contractions of intact and endothelium-free isolated PCA rings, stimulated by PAR1 /PAR2 -activating peptides, angiotensin-II, PGF2α , EGF, PDGF and KCl, were monitored with/without multiple signalling pathway inhibitors, including AG-tyrphostins AG18 (non-specific PYKs), AG1478 (EGF-receptor kinase), AG1296 (PDGF receptor kinase), PP1 (Src kinase), U0126 and PD98059 (MEK/MAPKinase kinase), indomethacin/SC-560/NS-398 (COX-1/2) and L-NAME (NOS). AG18 inhibited the contractions induced by all the agonists except KCl, whereas U0126 attenuated contractions induced by PAR1 /PAR2 agonists, EGF and angiotensin-II, but not by PGF2α , the COX-produced metabolites of arachidonate and KCl. PP1 only affected the responses to PAR1 /PAR2 -activating peptides and angiotensin-II. The EGF-kinase inhibitor, AG1478, attenuated contractions initiated by the PARs (PAR2 >> PAR1 ) and EGF itself, but not by angiotensin-II, PGF2α or KCl. COX-1/2 inhibitors blocked the contractions induced by all the agonists, except KCl and PGF2α . PAR1/2 -mediated contractions of the PCA are dependent on Src and MAPKinase and, in part, involve EGF-receptor-kinase transactivation and the generation of a COX-derived contractile agonist. However, the PYK signalling pathways used by PARs are distinct from each other and from those triggered by angiotensin-II and EGF. These signalling pathways may be therapeutic targets for managing coagulation-proteinase-induced coronary vasospasm.

Mechanism of glucose-6-phosphate dehydrogenase-mediated regulation of coronary artery contractility

We previously identified glucose-6-phosphate dehydrogenase (G6PD) as a regulator of vascular smooth muscle contraction. In this study, we tested our hypothesis that G6PD activated by KCl via a phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-protein kinase C (PKC) pathway increases vascular smooth muscle contraction and that inhibition of G6PD relaxes smooth muscle by decreasing intracellular Ca(2+) ([Ca(2+)](i)) and Ca(2+) sensitivity to the myofilament. Here we show that G6PD is activated by membrane depolarization via PKC and PTEN pathway and that G6PD inhibition decreases intracellular free calcium ([Ca(2+)](i)) in vascular smooth muscle cells and thus arterial contractility. In bovine coronary artery (CA), KCl (30 mmol/l) increased PKC activity and doubled G6PD V(max) without affecting K(m). KCl-induced PKC and G6PD activation was inhibited by bisperoxo(pyridine-2-carboxyl)oxovanadate (Bpv; 10 μmol/l), a PTEN inhibitor, which also inhibited (P < 0.05) KCl-induced CA contraction. The G6PD blockers 6-aminonicotinamide (6AN; 1 mmol/l) and epiandrosterone (EPI; 100 μmol/l) inhibited KCl-induced increases in G6PD activity, [Ca(2+)](i), Ca(2+)-dependent myosin light chain (MLC) phosphorylation, and contraction. Relaxation of precontracted CA by 6AN and EPI was not blocked by calnoxin (10 μmol/l), a plasma membrane Ca(2+) ATPase inhibitor or by lowering extracellular Na(+), which inhibits the Na(+)/Ca(2+) exchanger (NCX), but cyclopiazonic acid (200 μmol/l), a sarcoplasmic reticulum Ca(2+) ATPase inhibitor, reduced (P < 0.05) 6AN- and EPI-induced relaxation. 6AN also attenuated phosphorylation of myosin phosphatase target subunit 1 (MYPT1) at Ser855, a site phosphorylated by Rho kinase, inhibition of which reduced (P < 0.05) KCl-induced CA contraction and 6AN-induced relaxation. By contrast, 6AN increased (P < 0.05) vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser239, indicating that inhibition of G6PD increases PKA or PKG activity. Inhibition of PKG by RT-8-Br-PET-cGMPs (100 nmol/l) diminished 6AN-evoked VASP phosphorylation (P < 0.05), but RT-8-Br-PET-cGMPs increased 6AN-induced relaxation. These findings suggest G6PD inhibition relaxes CA by decreasing Ca(2+) influx, increasing Ca(2+) sequestration, and inhibiting Rho kinase but not by increasing Ca(2+) extrusion or activating PKG.

An estrogen‐induced decrease in voltage‐gated calcium channel expression attenuates coronary artery contractility

Estrogen (E2) can pharmacologically inhibit Ca2+ influx into vascular smooth muscle cells. However, little is known about the ability of E2 to alter vascular Ca2+ channel expression. The goal of our study was to determine if a physiological E2 concentration can decrease the expression of voltage‐gated calcium channels (VGCC) in small coronary arteries. Right coronary arteries were obtained from hearts of reproductively cycling sows. The distal end of the artery was cut into 4 mm rings or longitudinal strips and incubated for 24 hours in E2 (1 nM) or its ethanol solvent. Western blots using protein isolated from the arterial strips demonstrated a decreased expression of the pore‐forming α1C subunit of the VGCC in E2‐treated arteries. In parallel studies, isometric tension recording revealed that E2‐treated arterial rings contracted significantly less to 30 mM KCl. However, E2 and ethanol‐treated rings preconstricted with 60 mM KCl showed similar relaxation responses to E2 (1 nM to 1 μM). These findings suggest that physiological concentrations of E2 down‐regulate VGCC, thereby providing a potentially novel mechanism for limiting coronary vasoconstriction. In the same arteries, E2‐dependent relaxation is intact. By limiting the expression of VGCC, E2 may promote coronary blood flow and potentially lower the incidence of coronary events in pre‐menopausal women. Support: NCRR of the NIH, Grant #P20 RR‐16460

Myosin Phosphatase Regulatory Pathways

In many ways, the smooth muscle cell (SMC) has been at the forefront in defining cellular signaling pathways. For example, the initial description of agonist-dependent intracellular calcium ([Ca2+]i) transients was made on vertebrate vascular SMC using aqueorin as the indicator.1 Delineation of nitric oxide (NO) and cGMP signaling was first accomplished in smooth muscle.2,3 And more recently, insights into the general mechanisms of gene transcription that dictate phenotypic traits of cells are being defined by smooth muscle specific gene expression.4,5 It should come as no surprise then that the interactions among many signaling pathways in cells should be explained first in the SMC. Perhaps the reason for the central position of the SMC in defining paradigms in cellular biology is that there are well-defined physiologic end points amenable to measurement (ie, contractile force) and even better described and easily quantified biochemical pathways that underlie said physiologic end points (ie, myosin regulatory light chain phosphorylation). From a historical perspective, the role of protein phosphorylation in smooth muscle contraction as a paradigm for cell signaling follows only that for the control of glycogen metabolism (see 6,7 for reviews). Increases in the levels of cytosolic [Ca2+]i initiate smooth muscle contraction by binding to the universal intracellular Ca2+ receptor protein, calmodulin (CaM), which in turn binds to and activates smooth muscle myosin light chain kinase (MLCK). Activated MLCK catalyzes the phosphorylation serine-19 of the regulatory myosin light chain (MLC) thereby increasing cross-bridge cycling and the rate of tension development. Dephosphorylation of MLC is catalyzed by smooth muscle specific myosin light chain phosphatase (MLCP). Decreases in cytosolic [Ca2+]i and MLC dephosphorylation are considered salient events in smooth muscle relaxation. What has become apparent only within the last decade is the fact that …

NEP inhibitors enhance C-type natriuretic peptide-induced relaxation in porcine isolated coronary artery

C-type natriuretic peptide (CNP), a local regulator of vascular tone and cell proliferation, is eliminated from the circulation via NPR-C receptors and neutral endopeptidase enzyme (NEP, EC. 3.4.24.11). The increased contractility of coronary arteries in different cardiovascular diseases made us study the possible enhancement of vasodilator capacity of exogenously added CNP with concomitant NEP inhibition on porcine coronary arteries in vitro. CNP (0.006–1.4 μM) concentration dependently relaxed the U46619 (0.07–0.4 μM) precontracted preparations in an almost equally effective manner in the presence and absence of functional endothelium with maximum effects of about 40%. The combined NEP/endothelin-converting enzyme inhibitor (NEP/ECE inhibitor), phosphoramidon (10 μM) or the specific inhibitor of the NEP, thiorphan (10 μM) resulted in an enhanced magnitude of CNP-induced relaxation without significant change in the EC 50 both on endothelium intact and endothelium deprived preparations. The inhibition of endothelin receptors by PD 142893 (10 μM) enhanced the relaxing effect of CNP in the presence but not in the absence of functional endothelium indicating a functional antagonism between CNP and endothelin. Our results suggest that inhibition of CNP degradation may endue this endogenous peptide with therapeutic potency in cardiovascular diseases.

Coronary artery contractility in fetal sheep during chronic high altitude hypoxia

Coronary artery contractility in fetal sheep during chronic high altitude hypoxia

Long-term estradiol replacement decreases contractility of guinea pig coronary arteries to the thromboxane mimetic U46619.

Estradiol replacement therapy reduces the incidence of coronary artery disease. Current evidence suggests that estradiol may stimulate the production of endothelium-derived NO and thereby reduce the contractile response of vascular smooth muscle. We investigated the effect of long-term replacement of estradiol on NO release and its effect on coronary artery contractility. Female guinea pigs were ovariectomized and allowed to recover for 100 days. Pellets containing 17 beta-estradiol (0.25, 0.5, 1.5, and 7.5 mg released over 21 days) were placed subcutaneously for 19 to 20 days. Animals were then anesthetized, and the coronary arteries were excised and cut into ring segments. Rings were placed in small-vessel myographs for measurement of isometric force. Contractile responses of coronary arteries to cumulative addition of U46619 (10(-10) to 10(-5) mol/L), a thromboxane mimetic, were measured in the presence and absence of nitro-L-arginine (LNA), a selective NO synthase inhibitor, and methylene blue, a guanylate cyclase inhibitor. Low (0.25-mg) but not high (0.5-, 1.5-, or 7.5-mg) doses of estradiol inhibited the maximal contractile responses to U46619 compared with arteries from untreated castrated animals. In addition, both LNA and methylene blue potentiated contractile responses to U46619 of arteries from animals receiving 0.25 and 0.5 mg but not 1.5 and 7.5 mg estradiol. Negative log EC50 values were significantly inhibited at 0.25 and 7.5 mg but unaffected at 0.5 and 1.5 mg estradiol compared with castrated animals. Estradiol at low doses may protect against vasospasm by stimulating endothelium-derived NO release and inhibiting coronary artery contractility.

Mechanisms mediating the vasodilatory effects of N-hydroxy- l-arginine in coronary arteries

We assessed the mechanisms of action of N G-hydroxy- l-arginine in isolated porcine large coronary arterial rings. Increasing (1, 10 and 100 μM) concentrations of N G-hydroxy- l-arginine evoked endothelium-dependent dilation which was eliminated by 100 μM of N G-nitro- l-arginine methyl ester, but not affected by a cytochrome P 450 inhibitors (miconazole or 7-ethoxyresorufin). At a given concentration, the dilatory response to N G-hydroxy- l-arginine was stronger than that elicited by l-arginine. N G-Hydroxy- l-arginine (100 μM), but not N G-hydroxy- d-arginine, potentiated the endothelium-dependent dilation of calcium ionophore A23187 but had no effect on endothelium-independent dilation evoked by an NO donor. NO release by endothelium-intact porcine coronary arterial rings was measured with a chemiluminescence analyser. A23187 (10 μM), N G-Hydroxy- l-arginine (100 μM), and to a lesser extent N G-hydroxy- d-arginine (100 μM), significantly increased NO concentration over 15 min observation period. When A23187 and N G-hydroxy- l-arginine were combined, NO concentration increased in an additive fashion. Enhanced No release by either A23187, N G-hydroxy- l-arginine or N G-hydroxy- d-arginine was attenuated by N G-nitro- l-arginine methyl ester. We conclude that N G-hydroxy- l-arginine exerts its effects on the contractility of coronary arteries by acting as a substrate for the endothelial nitric oxide synthase leading to enhanced NO production. Cytochrome P 450 were not involved the dilatory response to N G-hydroxy- l-arginine. In this respect, porcine coronary arteries differ significantly from cultured smooth muscle cells in metabolising N G-hydroxy- l-arginine.

Reoxygenation-induced relaxation of coronary arteries. A novel endothelium-dependent mechanism.

Coronary artery contractility is well known to be modulated by oxygen partial pressure. Both smooth muscle and the endothelium contribute to coronary artery oxygen sensitivity. Mechanisms underlying endothelium-dependent effects of oxygen include the sensitivity of the nitric oxide/endothelium-derived relaxing factor (EDRF), hydrogen peroxide, and eicosanoid pathways. In the present study, we characterize a novel endothelium-dependent component of porcine coronary artery oxygen sensitivity that is independent of these known pathways. Porcine coronary arteries were stimulated with either KCl or U46619. Hypoxia elicited a transient increase in force that was much greater in endothelium-intact arteries. This effect was abolished by nitric oxide/EDRF pathway inhibitors NG-monomethyl-L-arginine and N-nitro-L-arginine. In the steady state, hypoxia reduced isometric force to a similar degree in both intact and denuded arteries. Reoxygenation elicited a rapid and transient relaxation only in intact arteries. In contrast, this endothelium-dependent relaxation was not inhibited by nitric oxide/EDRF pathway inhibitors nor inhibitors of other potential oxygen-sensitive pathways, such as indomethacin, aminotriazole, superoxide dismutase, catalase, propranolol, or ouabain. The reoxygenation relaxation was, however, sensitive to very low levels of oxygen and was inhibited by cyanide and rotenone, suggesting an involvement of mitochondrial metabolism. Interestingly, the relaxation response to reoxygenation, similar to that for substance P, could be restored in denuded arteries by coupling with an endothelium-intact donor artery. This "sandwich" experiment suggests that the endothelium dependence is mediated by a transmissible factor. Our results indicate that a novel class of endothelium-dependent factors may contribute to coronary artery responses to changes in oxygen partial pressure.