Effects of diabetes and of injury on muscle protein in the mouse,and their interaction

Summary The effects of a 20% dorsal scald injury and of different severities of streptozotocin diabetes on hindquarter muscle protein have been studied in the mouse. Ten days after scald injury muscle protein contents were generally unaffected, whereas moderate diabetes (200 mg streptozotocin/kg body weight; plasma glucose concentrations 17–46 mmol/l; normal 11 mmol/l) led to net loss of muscle protein. Production of scald injury in the moderately diabetic mouse caused significant additional loss of muscle protein, especially from the extensor digitorum longus. Milder diabetes (maximum plasma glucose concentration 15 mmol/l) did not lead to loss of muscle protein. However, scald injury in the mildly diabetic mouse caused significant loss of protein from all muscles studied. The effects of diabetes and of injury on loss of muscle protein were at least additive and in some muscles probably synergistic.     

Prolongation of tension on reoxygenation following myocardial hypoxia: a possible role for mitochondria in muscle relaxation.

The mechanism for tension prolongation during reoxygenation following myocardial hypoxia was investigated. It was found that prior addition of isoproterenol, reserpine, quinidine, lidocaine and insulin or a change in pH, temperature, stimulation rate, preload or duration of hypoxia did not qualitatively alter the appearance of the phenomenon. On reoxygenating hypoxic preparations in the presence of 5, 10 or 20% oxygen, tension prolongation was clearly present when little increase in isometric tension was evident. Inhibition of glycolysis by iodoacetate did not alter the appearance of the phenomenon during reoxygenation. Three respiratory inhibitors, antimycin A, rotenone and cyanide, at concentrations which did not prevent an increase in isometric tension during recovery from myocardial hypoxia, all completely prevented the appearance of tension prolongation. Two uncouplers of oxidative phosphorylation, 2–4 dinitrophenol and carbonyl cyanide m-chlorophenyl hydrazone at concentrations large enough to lead to mechanical deterioration despite the presence of oxygen, failed to prevent the appearance of tension prolongation upon reoxygenation. It is concluded that myocardial respiratory activity, independent of ability to generate high energy phosphate, appears capable of altering the duration of mechanical events during reoxygenation of hypoxic heart muscle.     

葛根素诱导血管平滑肌细胞凋亡的实验研究

目的：观察葛根素促进人脐动脉血管平滑肌细胞凋亡的作用，探讨葛根素抑制平滑肌细胞增殖的机制。方法：分离培养人脐动脉平滑肌细胞，不同浓度葛根素与细胞孵育，TUNEL检测葛根素诱导细胞凋亡，rt-PCR实验检测促凋亡基因Bax和抗凋亡基因Bcl-XL。结果：随着葛根素浓度升高，细胞生长受抑制，TUNEL阳性细胞显著增加。rt-PCR实验发现促凋亡基因Bax随药物浓度和作用时间的增加而上升，而且Bax、Bcl-XL基因表达比例有一定升高。结论：葛根素通过调节经典的Bax、Bcl-XL通路对血管平滑肌细胞凋亡有一定诱导作用。     

Acute infarction of the left ventricular papillary muscle: Electrocardiographic pattern and recognition of its location

Background and hypothesis: ST-segment depression during acute myocardial infarction (AMI) is known to herald serious hemodynamic complications. Since the mechanism of this dependence is not clear, we reinvestigated the old concept of papillary muscle infarction (PMI) as a cause of marked ST depression. Methods: Autopsies and morpho-electrocardiographic correlations were performed in 53 patients with AMI involving one or both left ventricular papillary muscles, and in 10 patients with AMI, but without acute PMI. Results: ST-segment depression ≥l mm in at least two leads (mean 3.6 ± 2.2 mm) was found in 46 (86.8%) patients with, and in one without acute PMI. Thus, the sensitivity and specificity in selecting patients with acute PMI from among those with AMI were 86.8 and 90%, respectively, with an overall accuracy of diagnosis of acute PMI in the course of AMI of 87.3%. Among 26 patients with ST elevation consistent with diagnosis of AMI, ST depression, recorded in 22 patients, was insignificantly greater than in 24 of 27 patients without ST elevation: 4.1 ± 2.9 versus 3.1 ± 1.2 mm. Localization of ST depression in the limb leads allowed recognition of which papillary muscle suffered from acute infarction: ST depression in the inferior leads was seen only in patients with anterolateral PMI, whereas in leads I and/or aVL it was seen only in cases with posteromedial PMI. This rule was also valid in patients without concomitant ST elevation. Conclusion: Patients with acute PMI show marked ST-segment depression. Its location in the limb leads allows recognition of which papillary muscle has undergone necrosis. This cause of marked ST depression in patients with AMI may explain the high mortality in this particular group.     

GLP-1(7-36)amide binding in skeletal muscle membranes from streptozotocin diabetic rats

A higher specific binding of GLP-1(7–36)amide is found in skeletal muscle plasma membranes from adult streptozotocin (STZ)-treated rats (insulin-dependent diabetes mellitus model) and from neonatal STZ-treated rats (non insulin-dependent diabetes mellitus model), as compared to that in normal controls; no apparent change in the affinity was observed, that indicating the presence in both diabetic models of an increased number of high affinity binding sites for the peptide. The maximal specific GLP-1(7–16)amide binding in the non insulin-dependent diabetes mellitus model was found to be significantly higher than that in the insulin-dependent diabetes mellitus model. As GLP-1(7–36)amide exerts a glycogenic effect in the rat skeletal muscle, the present data suggest that the action of the peptide in the muscle glucose metabolism may be increased in states of insulin deficiency accompanied or not by insulin resistance.     

L-Cysteine Increases Glucose Uptake in Mouse Soleus Muscle and SH-SY5Y Cells

Previous investigation demonstrated the potential of L-cysteine (L-Cys) at high concentrations to cause hypoglycemia in mice totally deprived of insulin. For further elucidation of the glucose-lowering mechanism, glucose uptake and quantity of glucose transporters (GLUTs 3 and 4) in mouse soleus muscle and C2C12 muscle cells, as well as in human SH-SY5Y neuroblastoma cells, were investigated. A marked enhancement of glucose uptake was demonstrated, peaking at 5.0 mM L-Cys in soleus muscle (P < 0.05) and SH-SY5Y cells (P < 0.001), respectively. In contrast, glucose uptake was not affected in the C2C12 muscle cells. Kinetic analysis of the SH-SY5Y glucose uptake showed a 2.5-fold increase in maximum transport velocity compared with controls (P < 0.001). In addition, both GLUT3 and GLUT4 levels were increased following exposure to L-Cys. Our findings point to a possible hypoglycemic effect of L-Cys.     

Regulation of VEGF and bFGF mRNA expression and other proliferative compounds in skeletal muscle cells

The role of muscle contraction, prostanoids, nitric oxide and adenosine in the regulation of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and endothelial cell proliferative compounds in skeletal muscle cell cultures was examined. VEGF and bFGF mRNA, protein release as well as the proliferative effect of extracellular medium was determined in non-stimulated and electro-stimulated rat and human skeletal muscle cells. In rat skeletal muscle cells these aspects were also determined after treatment with inhibitors and/or donors of nitric oxide (NO), prostanoids and adenosine. Electro-stimulation caused an elevation in the VEGF and bFGF mRNA levels of rat muscle cells by 33% and 43% (P < 0.05), respectively, and in human muscle cells VEGF mRNA was elevated by 24%. Medium from electro-stimulated human, but not rat muscle cells induced a 126% higher (P < 0.05) endothelial cell proliferation than medium from non-stimulated cells. Cyclooxygenase inhibition of rat muscle cells induced a 172% increase (P < 0.05) in VEGF mRNA and a 104% increase in the basal VEGF release. Treatment with the NO donor SNAP (0.5 M) decreased (P < 0.05) VEGF and bFGF mRNA by 42 and 38%, respectively. Medium from SNAP treated muscle cells induced a 45% lower (P < 0.05) proliferation of endothelial cells than control medium. Adenosine enhanced the basal VEGF release from muscle cells by 75% compared to control. The present data demonstrate that contractile activity, NO, adenosine and products of cyclooxygenase regulate the expression of VEGF and bFGF mRNA in skeletal muscle cells and that contractile activity and NO regulate endothelial cell proliferative compounds in muscle extracellular fluid.     

The necessity of using two parameters to describe isotonic shortening velocity of muscle tissues: the effect of various interventions upon initial shortening velocity (vi) and curvature (b)

Summary In skinned skeletal muscle fibers and skinned preparations of myocardium or smooth muscle, for all conditions studied, the length traces during isotonic shortening are always found to be significantly curved. It is demonstrated that the observed curvature is not simply due to inhomogeneities on the sarcomere level in striated muscle, damaged ends of the preparations, double overlap and collision of filaments, or depletion of MgATP during the period of isotonic shortening. It is shown that the velocity of shortening can be described by an exponential function: v=v_i exp (-b[SL_i-SL]) with SL_i: sarcomere length at the start of the release; SL: sarcomere length during isotonic shortening. Thus, instantaneous shortening velocity (v) is determined by two parameters: v_i, the initial shortening velocity for SL=SL_i, and b, a constant characterizing the decrease in velocity during isotonic shortening. Factors which affect isotonic shortening can do this by affecting v_i, or by changing b, or both. Therefore, when analysing the effects of interventions which affect instantaneous shortening velocity, these two possibilities have to be distinguished. Since curvature of the length traces might be caused by noncrossbridge components, only v_i, the initial speed of shortening, is a parameter which directly reflects kinetics of the cross-bridge cycle while instantaneous speed of shortening might also be affected by noncrossbridge factors.Analysing isotonic shortening in terms of v_i and b, the effects of ionic strength, free Ca⁺⁺ concentration, MgATP/MgADP ratio and temperature on unloaded isotonic shortening have been studied. For the conditions used, it can be shown that ionic strength and free Ca⁺⁺ concentration only affect b without significant effect on v_i, whereas MgATP/MgADP ratio and temperature affect both v_i and b. This means that of these factors only MgATP/MgADP ratio and temperature affect the crossbridge kinetics which determine the maximum speed of shortening while ionic strength and free Ca⁺⁺ concentration have no such effect within the experimental error.Dedicated to Prof. R. Jacob on the occasion of his 60th birthday.Supported by the Deutsche Forschungsgemeinschaft: Br 849/1-1.     

Myocardial injury following endogenous catecholamine release in rabbits

Catecholamines (CAT) given in large doses produce cardiomyopathic changes in several animal species. This study was designed to determine if endogenous release can also induce cardiac injury. Rabbits were infused with doses of tyramine (TYR), ranging from 200 to 500 micrograms/min/kg, i.v. for 90 min. Arterial pressure and heart rate were measured, as were total CAT concentrations, blood gases, pH and glucose. Two days later the animals were killed and cardiac injury assessed using a histological scoring system. All data were compared with controls given saline. Initial CAT averaged 452 pg/ml, rose to 2890 pg/ml after starting TYR, 500 micrograms/min/kg, and remained elevated for the duration of infusion. Circulating CAT levels were a function of TYR dose, and bore a linear relationship to the histological score (P less than 0.001). Development of lesions was unaltered by beta 1 blockade with practolol, but sharply reduced by alpha blockade with phentolamine (P less than 0.01). Pretreatment with insulin also reduced lesion formation, but diabetic (alloxan) rabbits showed no greater CAT injury. It is concluded that endogenous release of CAT induces myocardial injury in the rabbit in a dose-dependent manner. This is unrelated to myocardial O2 demand, and microvascular pathology was absent. Activation of alpha adrenergic pathways is likely the dominant or exclusive mechanism.     

Functional assessment of neuronal cannabinoid receptors in the muscular layers of human ileum and colon

BACKGROUND & AIMS: The notion that specific receptors account for the ability of natural and synthetic cannabinoids to alter physiological functions, prompted this study aimed at assessing their functional presence in the human gut. METHODS: The effects have been studied of cannabinoids and selective antagonists of their receptors on chemically or electrically evoked contractions in preparations of human intestinal smooth muscle in vitro. RESULTS: Atropine prevented the contractions of longitudinal and circular muscle strips of ileum and colon induced by carbachol or electrical field stimulation; tetrodotoxin abolished only the latter which suggests they do involve activation of cholinergic neurons. The synthetic cannabinoid (+)WIN 55,212-2 had no effect on carbachol contractions, but in a concentration-dependent fashion prevented those elicited by electrical field stimulation - which were insensitive to the putative endogenous cannabinoid anandamide - more potently in longitudinal than in circular strips. The selective CB1 receptor antagonist SR141716, which had no effect in the absence of (+)WIN 55,212-2, competitively antagonised its inhibition of electrical field stimulation contractions, unlike the selective CB2 antagonist SR144528. CONCLUSIONS: Cannabinoid CB1 receptors are functionally present in the human ileum and colon; their pharmacological activation apparently results in inhibition of excitatory cholinergic pathways subserving smooth muscle contraction.