摘要:

The contribution of sarcoplasmic reticulum (SR) Ca2+release to evoked tension in rat arterial rings was studied by comparing the effects of ryanodine (an SR Ca2+channel opener) and thapsigargin and cyclopiazonic acid (CPA) (two Ca2+-ATPase inhibitors). Isometric tension was evoked by serotonin (5-HT), 30–50 mM external K+, and 10 mM caffeine in rings of aorta and a small (second-order) branch of the superior mesenteric artery (SMA). Resting tension was unaffected by 10 μM ryanodine or 1–5 μM thapsigargin, but 20 μM CPA raised resting tension in aortic rings and evoked spontaneous contractions in some SMA rings. Ryanodine (10 μM) or 1–5 μM thapsigargin partially depleted the SR Ca2+stores (indicated by reduced caffeine-evoked contractions) and attenuated 5-HT- and high K+-evoked contractions in aortic rings but augmented 5-HT- and high K+-evoked contractions in SMA. Caffeine completely emptied the SR Ca2+stores in the presence of ryanodine but not thapsigargin in both the aorta and SMA; thus, thapsigargin may selectively affect one component of a heterogeneous SR. When the aortic Ca2+stores were empty (i.e., caffeine contractions were abolished), the 5-HT- and high K+-evoked contractions in the aorta were also augmented. CPA rapidly emptied the SR Ca2+stores in both the aorta and SMA. CPA augmented the 5-HT-evoked contractions in the SMA and in five of nine aortic rings but attenuated evoked contractions in the remaining aortic rings. The attenuation or abolition of the caffeine contractions implies that ryanodine, thapsigargin, and CPA all deplete the SR Ca2+stores. The attenuated responses to 5-HT and high K+observed when the aortic SR Ca2+stores were only partially depleted are consistent with the idea that evoked SR Ca2+release is a large component of the Ca2+transient in the aorta. The augmentation of 5-HT- and high K+-evoked responses after partial (SMA) or complete (aorta) depletion of the SR Ca2+stores suggests that evoked release of SR Ca2+normally regulates Ca2+entry by negative feedback and/or that the SR normally buffers the evoked rise in cytosolic Ca2+. (Circulation Research1992;70:968–977)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Phorbol esters, which activate protein kinase C, modulate vasoconstrictor-induced tension in vascular smooth muscle. We examined the effects of phorbol esters (phorbol 12,13-dibutyrate [PDBu] and 12-O-tetradecanoylphorbol 13-acetate [TPA]) on receptor agonist (serotonin [5-HT] and arginine vasopressin [AVP])-, high K+-, and caffeine-induced contractions in rings of rat aorta and a small (second-order) branch of the superior mesenteric artery (SMA). PDBu and TPA significantly augmented agonist-evoked contractions in aorta but diminished those in SMA. For example, 30 nM PDBu increased 5-HIT- and AVP-evoked contractions 2.0–2.5-fold in aorta (p<0.01) but decreased 5-HIT- and AVP-induced contractions by 40–60% in SMA (p<0.01). In contrast, PDBu and TPA amplified high K+- and 10 mM caffeine-induced contractions in both aorta and SMA. Augmentation of agonist-induced contractions by PDBu was greater in endothelium-denuded aorta than in intact aorta. Two protein kinase C antagonists, H-7 and staurosporine, inhibited 5-HT-evoked contractions in the absence as well as in the presence of PDBu in both types of arteries. The augmentation of contractile responses to caffeine and K+by phorbol esters in both types of arteries suggests that the phorbols increase the sensitivity of the contractile apparatus to Ca2+, probably by activating protein kinase C. However, the inhibitory effects of phorbols on 5-Hr- and AVP-evoked responses in SMA suggest that under these conditions the dominant effect of the phorbols is a marked reduction in the availability of Ca2+in the SMA but not in the aorta. (Circulation Research1992;70:978–990)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We investigated the effects of hypoxia/reoxygenation exposure on the barrier function of endothelial cell monolayers. Bovine pulmonary microvessel endothelial cells were grown to confluence on microporous filters (0.8-μm pore diameter) and exposed to hypoxia (0.1% O2or Po2∼1 mm Hg) for 2, 4, 12, or 24 hours, followed by reoxygenation with room air for a period ranging from 16 seconds to 2 hours. The transendothelial clearance rate of125I-albumin was measured to determine the permeability of endothelial monolayers. Permeability increased twofold or fivefold over control values after 1 hour of reoxygenation in monolayers that had been exposed to either 12 or 24 hours of hypoxia. The response occurred within 5 minutes of reoxygenation, increased maximally by 40 minutes, and remained elevated with continuous reoxygenation for up to 2 hours. The increase in permeability was associated with F-actin reorganization, a change to spindlelike cells, and injured mitochondria. Immunoblot analysis indicated that neither hypoxia alone nor reoxygenation changed CuZn superoxide dismutase (SOD), MnSOD, and catalase levels. However, release of superoxide anions (O2−) into the extracellular medium increased by twofold within 40–60 minutes of reoxygenation. Treatment of endothelial cells with CuZnSOD (100 units/ml) for the 24-hour hypoxia period prevented O2−generation and ∼50% of the increase in permeability. Higher CuZnSOD concentrations (≥200 units/ml) were not protective. Treatment with catalase (100–1,000 units/ml) inhibited the reoxygenation-induced increase in permeability at the highest catalase concentration (1,000 units/ml), suggesting a critical role of hydrogen peroxide in mediating the response. We conclude that reoxygenation of endothelial cells causes the generation of oxidants and that this mediates the increase in vascular endothelial permeability occurring during reoxygenation. The loss of endothelial barrier function may contribute to the pathogenesis of reperfusion tissue injury. (Circulation Research1992;70:991–998)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Sarcomeric actin genes, α-cardiac and α-skeletal, are coexpressed in neonatal rodent hearts and are regulated in response to hormonal and hemodynamic stimuli; however, their precise developmental pattern of expression has not been determined, and it is unknown whether they are coexpressed during senescence. We have, therefore, investigated the accumulation of sarcomeric actin transcripts in rat heart during fetal and postnatal development and with senescence by two different techniques: primer extension analysis with an oligonucleotide common to both sarcomeric actins and RNA hybridization with specific cardiac α-actin cRNA probes. We found that at 17–19 days in utero both isogenes are coexpressed and ce-skeletal actin mRNAs represent 28.0 ± 0.8% of the sarcomeric actin mRNA total. Skeletal actin mRNAs increase to 40% of the total 1 week after birth (NS,p=0.15), remain constant for 3 weeks, and decrease to less than 20% of the total in ventricles and atria of 1-month-old rats. The α-skeletal actin transcripts further decline to less than 5% of the total at 2 months of age and do not reaccumulate in senescent animals. There was no significant diflerence between male and female rat ventricles. By comparison with the known accumulations of α- and β-myosin heavy chain mRNAs, our results demonstrate that whatever the developmental stage the kinetics of expression for the sarcomeric myosin and actin multigene families are independent. (Circulation Research1992;70:999–1005)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We have isolated and characterized collagen type VI from murine, canine, and nonhuman primate hearts. In the three species studied, collagen type I was the major collagenous component of the cardiac interstitium (80% of total collagen), whereas collagen type VI represented ∼5% of total collagen. To define the exact distribution of collagen type VI and its possible interactions with other components of the cardiac extracellular matrix, collagen types I, III, IV, and VI, laminin, and fibronectin were localized in the rat myocardium by immunohistochemistry, using monospecific antibodies. In the rat myocardium, collagen type VI was prevalent in the media and adventitia of muscular arteries, in fine connective tissue septa, in the area surrounding capillaries, and in the delicate endomysium in proximity to myocardial cells. When compared with the immunohistochemical localization of collagen types I, III, and IV, laminin, and fibronectin, the continuity and hierarchical organization of the cardiac extracellular matrix became apparent. The matrix forms a continuous network extending from the pericardium to the endocardium. Furthermore, there is an arborescent hierarchy in the system such that collagen type I is more prevalent in the wider septa, collagen type III being more obvious in medium-sized branches, and fibronectin and collagen type VI prevailing in the terminal (pericellular) aspects of the network. In this pericellular location, fibronectin and collagen type VI, by means of specific interactions, may act as anchor components linking the myocardial cell basement membranes not only to the extracellular matrix but also to the cardiac interstitial cells. This continuity, organization, and coupling of the cardiac extracellular matrix appears well suited to integrate and distribute the physical stress generated by the continuous contraction and relaxation of the myocardium. (Circulation Research1992;70:1006–1017)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

High affinity agonist-binding (HAB) sites are formed from specific receptor interaction with guanine nucleotide-binding (Gi) proteins. To determine whether the release of endothelium-derived relaxing factor (EDRF) is regulated by specific receptor-Giprotein coupling, we treated bovine aortic endothelial cells with 100 ng/ml pertussis toxin (PTX) for 16 hours to effect receptor-Giprotein uncoupling. The degree of receptor uncoupling as measured by the loss of HAB sites for the α2-adrenergic receptor and bradykinin receptor was assessed by radioligand binding studies using partially purified bovine aortic endothelial cell membranes. The release of EDRF in response to UK14304 (an α2-adrenergic receptor agonist) and bradykinin stimulation was measured with a bioassay apparatus. The Giprotein isoforms were characterized by Western blotting, and complete ADP-ribosylation of these proteins was confirmed by PTX-catalyzed [32P]NAD ribosylation. PTX produced a greater inhibition of EDRF release via the α2-adrenergic receptor pathway compared with the bradykinin receptor pathway (80% versus 46%,p<0.01). This corresponded to the loss of HAB sites from the α2-adrenergic receptor and bradykinin receptor pathway (72% versus 46%,p<0.01) as compared with complete loss of both HAB sites in the presence of GppNHp (0.1 mM). Since loss of HAB sites from PTX-mediated receptor uncoupling parallels the inhibition of EDRF release, these data suggest that Giproteins contribute to a greater proportion of HAB sites derived from α2-adrenergic receptor rather than bradykinin receptor interaction and that the inhibition of EDRF release by PTX is mainly due to the loss of these HAB sites. The degree of HAB site formation from specific receptor-Giprotein coupling may serve as one mechanism for regulating EDRF release via different cell surface receptors. (Circulation Research1992;70:1018–1026)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Previous studies have demonstrated that endothelin-1 (ET-1) is a potent vasoconstrictor that decreases cardiac output and increases hematocrit. The present study was designed to determine if the rise in hematocrit and decrease in cardiac output are in part due to shifts of plasma from the vascular space to the interstitial space. Red blood cell volume and plasma volume were determined by using chromium-51-labeled erythrocytes and iodine-125-labeled albumin, respectively, in anesthetized, nephrectomized, splenectomized rats. The present study demonstrates that ET-1 increases mean arterial pressure and hematocrit. This effect is associated with an increase in total-body albumin escape, which is reflected by a marked reduction in whole-body plasma volume. ET-1 enhanced albumin escape primarily in the liver, lung, and heart at low doses. At high doses, albumin escape increased primarily in the liver, heart, and gastrointestinal tract but not the lung. The present study demonstrates that ET-1 increases hematocrit independent of splenic contraction or renal losses by enhancing loss of plasma volume to the interstitial space without affecting red blood cell volume. Because of the profound pressor effects of ET-1, it is likely that the plasma loss results from increased capillary hydrostatic pressure. (Circulation Research1992;70:1027–1034)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Previously, we have reported on the selective accumulation of an atrial-like myosin light chain-1 (ALC1) in different forms of human ventricular hypertrophy. The present study involves the determination of ALC1content in a control group and in patients with aortic stenosis or insufficiency before and 56 ± 23 months after valve replacement and compares the hemodynamic and angiographic parameters. ALC1was quantified densitometrically after two-dimensional electrophoretic resolution of biopsy specimens from the left ventricle and was expressed in percent of total ventricular light chain-l. The mean ALC1content was 11.2 ± 9.2% in preoperative aortic stenosis and 4.5 ± 1.4% in aortic insufficiency, both being significantly (p<0.001) higher than the control value of 0.3 ± 0.3%. After valve replacement, mean ALC1content was lower than before, 4.2 ± 3.3% (p<0.05) in stenosis and 3.4 ± 3.1% (p=NS) in insufficiency. Left ventricular systolic pressure yields a significant (p<0.01) linear correlation (r=0.45) with the ALC1content in all preoperative and postoperative patients. Patient group averages of ALC1content correlate directly with left ventricular systolic and end-diastolic pressure and wall thickness (r=0.94–0.98) and, in an exponential fashion, with peak systolic circumferential wall stress (r=0.98) but not with muscle mass or any other parameter. The ventricular ALC1binds to myosin in proportion to its occurrence in the myocardium. The content of the endogenous ventricular light chain-1 did not change under pathological hemodynamics. The response in expression of the ALC1to pressure and volume overload suggests an adaptational process. This seems to be confirmed by its lower content in the postoperative patient groups with improved hemodynamic parameters. (Circulation Research1992;70:1035–1043)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We evaluated dynamic effects of the carotid sinus baroreflex on ventriculoarterial coupling. In seven anesthetized, vagotomized dogs, we bilaterally isolated carotid sinuses and randomly changed carotid sinus pressure while measuring aortic pressure, aortic flow, and left ventricular pressure. Estimating left ventricular end-systolic elastance (Ees) and effective arterial elastance (Ea) on a beat-to-beat basis, we determined transfer functions from the carotid sinus pressure to Ees(HEes) and from the carotid sinus pressure to Ea(HEs) over the frequency range spanning 0.002–0.25 Hz. Both HEes, and HEaexhibited characteristics of a second-order low-pass filter. The gains of HEesand HEawere 0.085 ± 0.065 (mean ± SD) and 0.081 ± 0.049 mm Hg/ml/mm Hg, respectively. There were no significant differences in natural frequencies (0.039 ± 0.013 versus 0.039 ± 0.007 Hz) or damping ratios (0.65 ± 0.11 versus 0.64 ± 0.24). The results indicated that the carotid sinus baroreflex dynamically altered Eesand Eato the same extent in the process of stabilizing arterial pressure. Because the arterial system extracts maximal external work from a given heart when Eaequals Ees, the carotid sinus baroreflex appeared to be designed to regulate the ventricular and arterial properties to optimize the energy transmission from the left ventricle to the arterial system in anesthetized, vagotomized dogs. (Circulation Research1992;70:1044–1053)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Effects of ER-001533 (ER), a newly synthesized vasorelaxant, on the membrane currents were examined in single ventricular cells of guinea pigs. The patch-clamp technique was used in the “whole-cell” and “inside-out” patch configurations. In the whole-cell clamp condition, ER induced a time-independent K+-dominant current, which was inhibited by glibenclamide (1–3 μM), suggesting that ER activated the cardiac ATP-sensitive K+channel (KATP). To elucidate the mechanism of ER-mediated KATPchannel activation, the drug was applied to the inside-out patches before and after channel “run-down.” Since nucleotide diphosphates could induce the channel openings after complete run-down, effects of the drug on the nucleotide diphosphate-induced channel openings were also examined. Before run-down, ER activated the KATPchannel only in the presence of ATP. ER shifted the relation between [ATP]1and the channel activity to the right in a concentration-dependent fashion without a significant alteration of the slope. After channel run-down, ER did not affect the channel openings either in the absence or in the presence of UDP. However, ER could relieve the ATP-γ-S inhibition of the UDP-induced channel openings. Thus, we conclude that ER antagonizes the inhibitory effect of ATP on the KATPchannel in a competitive manner, thereby enhancing the channel openings. (Circulation Research1992;70:1054–1061)

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID