摘要:

Ventricular fibrillation is the most important cause of cardiac electrical instability leading to sudden death. Fibrillation is believed to be associated with complex three‐dimensional (3‐D) spatio‐temporal patterns of electrical excitation of the myocardium. However, to this date, such patterns have not been directly observed or characterized, and little is known about their dynamics. In this paper, we present results that strongly support the hypothesis that at least some cases of ventricular fibrillation in the structurally normal heart may be the result of a single 3‐D electrical scroll wave that moves rapidly throughout the ventricles, giving rise to complex patterns of cardiac muscle exc

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.505249000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

We investigated ischaemic and postischaemic mitochondrial and peroxisomal fatty acid oxidation capacity, ATP levels and regional function in 40 anaesthetized open chest cats subjected to 10 or 40 min of regional myocardial ischaemia with or without 3 h of reperfusion (n=10 in each situation). Following 10 min of ischaemia, the mitochondrial fatty acid oxidation capacity measured in tissue extracts from ischaemic tissue (nmol min‐1mg protein‐1) was reduced in both subepi‐ and subendocardium, but was normalized in reperfused tissue extracts from both wall layers (0.29±0.03 and 0.30±0.04 vs. 0.57±0.05 and 0.59±0.05,P<0.05). Peroxisomal fatty acid oxidation capacity in tissue extracts was unaffected by ischaemia and reperfusion. ATP levels and regional function measured in the LAD region was partly restored transmurally. After 40 min of LAD occlusion, mitochondrial fatty acid oxidation capacity was reduced, with higher activity in subepi‐ than in subendocardium (0.27±0.05 vs. 0.19±0.04,P<0.05). Reperfusion did not restore mitochondrial fatty acid oxidation capacity. Peroxisomal fatty acid oxidation capacity was increased in the ischaemic subendocardium compared with levels in non‐ischaemic subendocardium (0.53±0.02 vs. 0.45±0.03,P<0.05), with normalization at the end of reperfusion. ATP levels were non‐uniformly reduced during ischaemia and not repleted during reperfusion. Regional function recovered in circumferential segments but not in longitudinal segments following 40 min of ischaemia. In conclusion fatty acid oxidation enzymes seem to be more resistant to ischaemia in peroxisomes than in mitochondria. Mitochondrial fatty acid oxidation is fully reversible following shortlasting ischaemia, but remains depressed following prolonged ischae

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.498243000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Long‐lasting myocardial ischaemia reduces the density of sarcolemmal L‐type calcium channels (LCC). Ischaemic preconditioning protects the myocardium against development of infarction. The aim of this study was to investigate if ischaemia‐induced loss in LCC is affected by ischaemic preconditioning. Specific (+)‐[3H]isradipine binding to LCC was compared in membranes and homogenates from control and ischaemic regions of non‐preconditioned and ischaemically preconditioned hearts [two 10 min left anterior descending coronary artery (LAD) occlusions, each followed by 30 min reperfusion]. Biopsies were sampled after 60 min mid LAD occlusion from ischaemic and control (supplied by circumflex artery) regions. Sixty min ischaemia reduced binding density of specific (+)‐[3H]isradipine in membranes by 23±11% (n=7,P<0.05) in the non‐preconditioned group and by 20±8% (n=6,P<0.05) in the preconditioned group. Binding density in homogenates was reduced by 36±5% (n=5,P<0.05) in the non‐preconditioned group and by 21±5% (n=5,P<0.05) in the preconditioned group. The reductions in the two groups and reductions in membranes and homogenates were not statistically different. The dissociation constant of binding was similar in the groups. In conclusion, 60 min of ischaemia reduced the binding density of (+)‐[3H]isradipine in membranes and homogenates by 20–36%. The reduction in density of binding sites was not caused by redistribution of sarcolemmal LCC to an intracellular compartment. Ischaemic preconditioning did not affect the decline in binding

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.494229000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The aim was to study the passive biomechanical wall properties in the isolated duodenum, jejunum and ileum of the rat. The organ bath contained a Krebs–Ringer solution with 10‐2mMgCl2to abolish smooth muscle contractile activity. Stepwise inflation of an intraluminal balloon, in which the cross‐sectional area (CSA) was measured, provided the distension stimulus. The circumferential wall stress–strain distributions were computed from steady‐state values of these measurements and the unstressed wall thickness was measured in order to evaluate the passive elastic properties. The CSAs measured increased from duodenum to jejunum and to ileum (P<0.001). At the highest applied pressure load the CSA was 16.64±0.46 mm2for the duodenum, 18.70±0.53 mm2for the jejunum and 21.73±0.49 mm2for the ileum. The wall thickness was 0.19±0.01, 0.25±0.01 and 0.28±0.02 mm, in duodenum, jejunum and ileum, respectively (P<0.01). All segments showed stress–strain distributions that were exponential by nature. Applying the functionY=exp(a+bX) gave a median determination coefficient of 0.98 (quartiles 0.96–0.99). The duodenum was significantly stiffer than the two other segments. The values ofaandbwere 2.03±0.11 and 14.82±1.81, 1.39±0.20 and 13.15±1.42, and 1.13±0.13 and 10.69±0.65 for the duodenum, jejunum and ileum, respectively. Theadiffered between the duodenum and the other segments (P<0.001), whereas thebdiffered only between the duodenum and ileum (P<0.005). In conclusion, differences in the luminal CSA, wall thickness and elastic properties were found between the du

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.503248000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of substance P (SP) and the naturally occurring met‐enkephalin and the synthetic μ‐specific opioid agonist, DAGO (Tyr‐d‐Ala‐Gly‐N‐Methy‐Phe‐Gly‐ol) and the δ‐specific opioid agonist DADL (Tyr‐d‐Ala‐Gly‐Phe‐d‐Leu) on basal ventilation were investigated in halothane‐anaesthetized rats. Local injections of SP (0.75–1.5 nmol) in the ventrolateral medulla oblongata (VLM), e.g. nucleus paragigantocellularis, and nucleus reticularis lateralis increased ventilation because of an elevation of tidal volume. Met‐enkephalin induced a short‐lasting ventilatory depression mainly because of a depression of tidal volume. Activation of δ‐ and μ‐opioid receptors in the VLM by local application of DADL and DAGO, respectively, induced ventilatory depression, which was later in onset and more long‐lasting. Local administration of met‐enkephalin into the VLM also produced a long‐lasting inhibition of the SP‐induced ventilatory excitation. A similar blockade of the SP‐induced excitatory ventilatory response could be elicited by DADL but not by DAGO. This antagonistic effect was attenuated by local application of the δ‐opioid receptor antagonist ICI 154.129. We conclude that the naturally occurring met‐enkephalin as well as synthetic μ‐ and δ‐specific enkephalin analogues (DAGO and DADL, respectively) in VLM depress basal ventilation by an effect on inspiratory drive. There is a functional antagonism between activation of δ‐opioid rec

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.485232000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Quadriceps muscle and fibre cross‐sectional areas (CSA), torque and neural activation were studied in seven healthy males during 6 months of weight training on alternate days with six series of eight unilateral leg extensions at 80% of one repetition maximum. After training, the quadriceps cross‐sectional area increased by 18.8±7.2% (P<0.001) and 19.3±6.7% (P<0.001) in the distal and proximal regions respectively, and by 13.0±7.2% (P<0.001) in the central region of the muscle. Hypertrophy was significantly different between and within the four constituents of the quadriceps. Biopsies of the vastus lateralis at mid‐thigh did not show any increase in mean fibre cross‐sectional area. Maximum isometric voluntary torque increased by 29.6±7.9%–21.1±8.6% (P<0.01‐0.05) between 100° and 160° of knee extension, but no change in the optimum angle (110°‐120°) for torque generation was found. A 12.0±10.8% (P<0.02) increase in torque per unit area together with a right shift in the IEMG‐torque relation and no change in maximum IEMG were observed. Time to peak isometric torque decreased by 45.8% (P<0.03) but no change in time to maximum IEMG was observed. In conclusion, strength training of the quadriceps results in a variable hypertrophy of its components without affecting its angle‐torque relation. The increase in torque per unit area, in the absence of changes in IEMG, may indicate changes in muscle architecture. An increase in muscle‐tendon stiffness may account for the de

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.483230000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

This study was conducted to test the hypothesis that inhibitory reflexes from respiratory centres in the brain or respiratory muscles limit the central motor drive to limb muscles during exhaustive exercise in chronic hypoxia. Experiments were performed on five members of an expedition to the Himalayas, following 56–81 days at altitudes of 5200–7500 m. During the last minute of exhaustive maximal two‐legged cycling with and without 4% CO2inhalation performed on different days, repeated maximal voluntary handgrip contractions (MVC) over 60 s (5 s contraction, 5 s rest; ×6) were performed at rest and exhaustive exercise. MVC or rate of decay of MVC was unaffected by simultaneous engagement of a major fraction of the muscle mass (leg muscles) and a very high pulmonary ventilation. With 4% CO2, peak pulmonary ventilation during the exhaustive exercise increased further by 41 L min‐1(140–181 L min‐1;P<0.05) without affecting the handgrip strength. These findings suggest that during exhaustive exercise of large muscle groups in chronic hypoxia, both maximal voluntary contraction force and dynamic muscle contractile force are not limited by extreme activation of respiratory centre

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.493234000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The present study investigated the effect of 7 days of strenuous exercise on the quantity of xanthine oxidase and IGF‐I in muscle. Fifteen male military trainees performed 1 week of terrain marching and warfare exercises. Muscle biopsies and blood samples were obtained prior to and after the week. After the week, the number of xanthine oxidase immunoreactive cells, identified as capillary endothelial cells and leucocytes, and the number of IGF‐I immunoreactive cells, mainly vascular cells but also cells tentatively identified as satellite cells, were higher in the muscle (P<0.05). Plasma creatine kinase activity was 650% higher after the week (P<0.001) and the muscle content of hydroxyproline was elevated by 160% 2 months post‐exercise (P<0.05), both findings implying injury to the muscle. The present data provide a first observation of an elevated level of xanthine oxidase and IGF‐I in human skeletal muscle after exercise. It is proposed that both substances increased as a result of cellular damage: xanthine oxidase because of the influence of immunomodulators, and IGF‐I in association with regenerative processes. The increased expression of IGF‐I in the muscle could, however, also reflect cellular growth in response to an elevated load on the muscle and the v

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.492235000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of reduced Na+,K+pump capacity on contractile endurance and excitation‐induced changes in intracellular Na+content were investigated in isolated rat soleus and extensor digitorum longus muscles. Pre‐incubation with 10‐5mouabain increased the rate of force decline measured over the first 5–20 s of tetanic contraction from 0.32 to 0.94% s‐1and 1.4 to 4.6% s‐1in soleus and extensor digitorum longus muscles, respectively. Soleus muscles from K+‐deficient rats exhibited 54% reduction in the concentration of Na+,K+pumps and the force decline during 30 s of 60 Hz stimulation was increased from 0.53 to 1.15% s‐1. A similar change was induced in control muscles when a comparable reduction in the concentration of functional Na+,K+pumps was elicited by pre‐incubation with ouabain (10‐6‐2×10‐6m). In soleus, the force decline during 60 s of 60 Hz stimulation showed linear correlation to the increase in intracellular Na+content. In extensor digitorum longus, force decline and increase in Na+content during 60 Hz stimulation were both four times faster than in soleus as measured over 15 s of excitation. These results indicate that during maximal contractions the Na+,K+pump capacity is one of the determinants for the contractile endurance in skeletal muscle. Furthermore, the maintenance of contractile force seems to be a function of the rate of Na+‐influx and this relationship may account for the difference in endurance between slow‐tw

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.d01-748.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Skeletal muscle buffering capacity (βmtitr) was determined in soleus (type I) and superficial vastus (type II) muscles of 16 Long–Evans rats with differing levels of spontaneous activity and in 11 sedentary control rats. βmtitrwas 24% higher (P<0.001) in superficial vastus muscle than in soleus muscle (268±50 vs. 216±30 μmol H+g muscle dry wt‐1pH unit‐1) (mean±SD). There was no relationship between βmtitrand mean weekly running distance amongst spontaneously running rats, nor was βmtitrany greater in these rats than in a group of sedentary control rats. Protein to wet wt ratio was 31% higher (P<0.0001) in the superficial vastus muscle when compared with soleus muscle (22.04±3.74 vs. 16.77±3.00 mg protein, 100 mg wet wt muscle‐1), but there was no relationship between protein to wet wt ratio and running distance. Initial muscle homogenate pH (pHi) was lower in superficial vastus muscle compared with soleus muscle (6.36±0.25 vs. 6.63±0.16). Running rats had a significantly lower pHiin both soleus and superficial vastus than sedentary controls. There was an exponential relationship between weekly running distance and pHiin both the superficial vastus muscle (r=‐0.86,P<0.001) and the soleus muscle (r=‐0.73,P<0.01). Citrate synthase activity correlated with weekly running distance in superficial vastus muscle (r=0.66,P<0.01) but not in soleus muscle. The results confirm a higher βmtitrin the type II superficial vastus muscle when compared with the predominantly type I soleus muscle. We suggest that this may be partly the result of a higher protein concentration in type II muscle. Future studies measuring βmtitrin mixed muscle (e.g. human vastus lateralis) should repo

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.488225000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY