Retinol influences contractile function and exerts an anti-proliferative effect on vascular smooth muscle cells through an endothelium-dependent mechanism

 Rat aortic rings maintained in organ culture for as little as 24 h show significant loss of contractile responsiveness to different agonists. Smooth muscle cells (SMC) in culture quickly de differentiate into a non-contractile phenotype with a marked capacity for proliferation. Rat aortic ring segments cultured in retinol supplemented (10^–6 M) medium showed significantly increased active tension development in response to 80 mM K⁺ depolarization compared with 7-day cultured control rings. The improvement of contractile performance of the cultured aorta segments in retinol-supplemented media was lost when rings were denuded of endothelium prior to culture, suggesting the endothelial cell layer as the mediator of this effect. Retinol at concentrations up to 10^–5 M was found to have no direct effect on proliferation of cells of the A7r5 SMC. However, retinol was found to augment significantly the growth inhibition of A7r5 cells grown in co-culture with bovine aortic endothelial cells (BAEC). It was further observed that media conditioned with BAEC treated with 10^–6 M retinol expressed SMC growth inhibitory properties compared with media conditioned by untreated BAEC cells or unconditioned media. Examination of cultured rat aortic ring segments by electron microscopy and BAEC cells with phase contrast microscopy revealed that retinol had obvious effects on endothelial cell morphology and ultrastructure. These results indicate that retinol exerts its effects primarily on the endothelium, which in turn secretes stable factors that directly affect SMC proliferation and contractility. Received: 12 December 1996 / Received after revision: 14 April 1997 / Accepted: 7 July 1997     

悬吊大鼠后肢骨骼肌等长收缩功能变化的动态特征

目的观测模拟失重1、2和4周大鼠比目鱼肌与趾长伸肌收缩性能的变化,并分析萎缩比目鱼肌收缩性能变化的可能机制.方法采用离体骨骼肌肌条灌流技术,观测比目鱼肌与趾长伸肌的等长收缩功能.结果悬吊1周大鼠比目鱼肌即出现萎缩,悬吊2周与4周进一步萎缩,在各时间点两组的差别均具有显著性或非常显著性意义.比目鱼肌等长收缩的最大张力在悬吊第1周仅呈降低趋势[对照组(1.76±0.18)g/mm2,悬吊组(1.46±0.26)g/mm2,P＞0.05],第2周的降低具有显著性意义[(1.25±0.09)g/mm2,P＜0.05],第4周则进一步降低[(0.90±0.06)g/mm2,P＜0.01].悬吊1周组大鼠趾长伸肌的最大张力未改变,2周与4周组的降低具有非常显著性意义(P＜0.01).悬吊1、2和4周组大鼠比目鱼肌等长收缩达到最大张力一半的时间与同步对照组相比,两组间的差别均无显著性意义(P＞0.05),但是,悬吊1与2周组达到最大张力的时间与从张力峰值到舒张75%的时间缩短(P＜0.05),悬吊4周组则进一步缩短(P＜0.01).与同步对照组相比,悬吊组趾长伸肌的时间参数均未发生改变(P＞0.05).结论由于比目鱼肌最大张力的降低与其萎缩在发生时间上不同步,而等长收缩的时间参数却较早发生改变,提示模拟失重萎缩比目鱼肌中调节性收缩蛋白可能较早发生改变,进而影响收缩性能.     

Cardiac modifications occurring in the ascitic rat with biliary cirrhosis are nitric oxide related

Background/Aims: Although the cardiac output is increased in liver cirrhosis, some degree of cardiac failure could coexist as suggested by human investigations showing cardiac enlargement in cirrhosis and by animal studies describing a limited response to fluid loading in the cirrhotic rat. Endotoxemia induces similar hemodynamic changes during the septic shock. This septic cardiomyopathy has been attributed to an increased secretion of nitric oxide by the myocytes. In this study, we aimed to verify if cirrhotic cardiomyopathy was present in the rat with biliary cirrhosis, and if it could be related to abnormal nitric oxide secretion.Methods: We therefore compared the coronary pressure, the systolic ventricular pressure and the peak rate of rise of the left ventricular pressure obtained from isolated hearts perfused with a modified Langedorff apparatus in control rats and in cirrhotic rats obtained by bile duct ligation. The variations occurring after inhibition of nitric oxide synthesis by the addition of N^g monomethyl-L-arginine (10⁻⁶M) to the perfusing Krebs-Ringer solution wee also studied in both groups.Results: We found that the coronary pressure and the contractility of the cirrhotic hearts decreased significantly when compared to the controls. Inhibition of the nitric oxide synthesis increased those values significantly when the hearts were obtained from cirrhotic animals. This was not observed in the control group.Conclusion: Our data suggest that the cardiac modifications induced by the cirrhosis in the studied parameters are related to nitric oxide.     

Protopine对肠鼠心乳头肌动作电位和收缩力的影响

采用常规微电极技术,用离体肠鼠心乳头肌观察了Protopine对正常心肌细胞动作电位和收缩力的影响。结果表明:Protopine产生浓度依赖性负性肌力作用。Vmax也呈现浓度依赖性降低,APD20、APD50、APD90不呈现浓度依赖性变化,但ERP随Protopine的浓度增加不断延长。提示Protopine的抗心律失常作用可能与ERP的延长有关。     

Pre-ejection Period: Measuring Beta-adrenergic Influences Upon the Heart

Increasing interest among psychophysiologists in sympathetic (beta-adrenergic) influences upon the heart has created the need for noninvasive techniques for assessing these influences. The validity of pre-ejection period (PEP), a systolic time interval, as a measure of beta-adrenergic influences upon myocardial contractility is evaluated. Details of a procedure for determining PEP using a polygraph and digital computer are presented. This methodology is then applied to an experiment in which the intracardiac (PEP) and arterial subintervals of pulse transmission time (PTT) are measured during biofeedback-assisted control of PTT in order to evaluate the relative contribution of changes in PEP to PTT control.     

Effects of contrast media used in angiocardiography on the mechanical performance and the relaxation of normal and ischaemic myocardium

The aim of this study was to investigate the mechanisms of thecardiodepressive action of ionic and non-ionic contrast mediacurrently used in coronary arteriography. Experiments carried out on isolated preparations of cat papillarymuscle, treated with increasing concentrations of Telebrix 39,Radioselectan, Hexabrix and Iopamidol 370 and 300, on the onehand and, on the other hand, a pre- determined dose of Telebrixand Iopamidol 300 during hypoxia and subsequent reoxygenation,showed that, at constant Ca²⁺ concentrations: (1) The cardiodepressive effects of contrast media are correlatedwith the hyperosmolality that they induce. When osmolality washigher than 400 mOsm, all the products caused a reduction ofthe peak force (PF: 40–49±5–15 %), the maximumvelocity of contraction (V_max: 39-85±3–66 %) andof the peak velocity of relaxation (V_relax: 23-30±2-20%) (P<0-01). The time to peak force (TPF), on the other hand,remained constant, whereas the half-relaxation time (THR) wasincreased. No significant differences were observed betweenthese effects and those induced by control iso-osmolar solutionswhen the same osmolality was induced. In practice, however, the critical hyperosmolality value of400 mOsm is never reached when using non-ionic contrast mediasuch as Hexabrix and Iopamidol 300. This could explain the excellenttolerance to these substances. (2) During hypoxia and reoxygenation, the effect ofhyperosmolalityis more marked. Thus, the non-ionic contrast medium, Iopamidol300 (340 mOsm), reduces the hypoxic contractility depression(PF: 53-10±2-60% compared to the control values of47-60±5-00%,P<0-01), whereas, at the same dose, the ionic medium Telebrixis hyperosmolar (440 mOsm) and induces a more pronounced hypoxicdepression of contractility (P<0-01). The critical hyperosmolality is never reached during ventriculography(320 mOsm), whatever the medium used, but it can be observedduring coronary arteriography. It is, therefore, important touse non-ionic contrast media in the investigation of unstableangina and of acute myocardium infarction.     

Regulation of the smooth muscle contractile phenotype by nonmuscle myosin

The contractile phenotype of a smooth muscle can broadly be classified as phasic or tonic. Following activation, phasic smooth muscle exhibits an initial period of rapid force activation, following which force falls to a lower steady state level. In contrast, force generated by tonic smooth muscle rises slowly to a sustained steady state. The differences in contractile patterns cannot be explained by the time course of either the Ca(2+) transient or phosphorylation of the 20-kDa regulatory myosin light chain (MLC(20)). Therefore, a molecular marker that defines tonic and phasic smooth muscle contractile properties remains elusive. Further, smooth muscle can maintain force at low levels of MLC(20) phosphorylation; often referred to as the latch state. The mechanism for the latch state is unknown and has been hypothesized to be due to a number of mechanisms including the formation of slowly cycling dephosphorylated or latch cross-bridges (Hai and Murphy, Am J Physiol 253:H1365-H1371, 1988). This review will focus evidence suggesting that nonmuscle myosin IIB (NMIIB) are the latch cross-bridges in smooth muscle and NMIIB content could define the tonic contractile phenotype.     

血管环模型的研究进展

血管环模型在新药筛选和病理生理基础研究中占有重要地位。目前血管环的研究类型主要包括两大类:血管收缩活性研究和血管生成活性研究。血管收缩活性研究涉及的疾病领域宽广,包括高血压、脑供血不足、充血性心力衰竭等。血管生成活性研究则主要集中在抗肿瘤研究和动静脉吻合的研究上。随着新技术和新思路的引进,血管环实验在相关领域的新药研发、基础研究等方面发挥着重要的作用。     

Effects of bone marrow mesenchymal stem cells in a rat model of myocardial infarction

Aim

Infusion of bone marrow mesenchymal stem cells (MSCs) improves myocardial function following myocardial infarction (MI). The mechanisms, however, remain controversial. This study was to investigate changes of MSCs in vivo after administration into myocardial infarcted rats. Our hypothesis was that MSCs might differentiate into contractile myocytes and improve myocardial function in vivo.

Methods

MI was induced in 21 Sprague–Dawley rats by ligation of the left anterior descending artery. One week after ligation, 18 rats were randomized to receive MSCs labeled with PKH26 in a phosphate buffer solution (PBS) by direct injection into the infarcted myocardium. The remaining 3 rats received PBS alone as placebo. An additional 3 non-ligated rats served as a normal group to obtain normal myocytes.

Results

Every week for 6 weeks, hearts from 3 rats injected with MSCs were harvested to observe single cardiomyocytes. Although each week numerous round MSCs were found in the hearts of animals treated with MSCs, beating cardiomyocyte-like cells labeled with PKH26 were observed at the sixth week. The contractility of cardiomyocyte-like cells was the same to that of the unlabeled contractile native cardiomyocytes at the sixth week and that of the normal group (10.71 ± 1.59 vs. 11.09 ± 3.42 vs. 11.21 ± 2.16, p > 0.05). The contractility of cardiomyocyte-like cells was greater than cells both from the first week (10.71 ± 1.59 vs. 7.37 ± 3.47, p < 0.01) and the second week (10.71 ± 1.59 vs. 8.08 ± 3.11, p < 0.05) which was associated with significantly increased ejection fraction.

Conclusions

MSCs can differentiate into beating cardiomyocytes in a rat model of MI and improve myocardial function.     

Effect of muscle dimensions on trabecular contractile performance under physiological conditions

Multicellular cardiac muscles are widely used to study cardiac (patho-)physiology in vitro. One of the potential pitfalls of such experiments is that muscles with a large diameter have a larger diffusion barrier for transport of oxygen and waste products and can thus potentially form a hypoxic core. Although a sufficiently small muscle size is critical for obtaining unambiguous data, the relationship between muscle diameter and contractile performance specifically under near-physiological conditions remains unknown. Small uniform trabeculae of various diameters isolated from LBNF1 rats were stimulated at different temperatures (27.5–37.5°C) and frequencies (1–8 Hz). Twitch contractions and rapid cooling contractures were used to assess contractile performance and SR Ca²⁺ load, respectively. We observed that at physiological frequencies and temperatures, contractile performance was clearly diminished in muscles with diameter >150 m, likely due to the decreased rates of oxygen supply and waste removal. At room temperature slower contractions allow sufficient time for oxygen diffusion into the muscle core, and as a result the difference in contractile performance between the thin and thick muscles was less. Thus, in order to exclude adverse effects on contractile performance in multicellular myocardium under physiological conditions, it is essential that the preparations are of sufficient small diameter (<0.15 mm).