Structure of the musculature of the chicken small intestine

Summary The small intestine of the chicken was studied by light and electron microscopy. The musculature, measuring about 180 m in thickness in the distended intestine, consists of four layers (outer longitudinal, outer circular, inner circular and inner longitudinal) which are directly apposed to one another. There is no layer of connective tissue equivalent to the submucosa of mammalian intestine, and the intestinal glands lie close to the inner longitudinal muscle. Mucosal folds are not formed during isotonic contraction of the intestine. The muscle cells of the chicken small intestine are characterized by large, numerous and sharply outlined dense bodies, by the presence of an extremely thin basal lamina, by prominent dense bands at the cell surface but relatively few intermediate junctions. There are many areas of direct apposition between cell membranes of adjacent cells and little collagen between the muscle cells. The four muscle layers have each distinctive structural features. Gap junctions between muscle cells occur only in the outer circular layer. The outer circular and outer longitudinal layers are closely apposed and numerous junctions of the adherens type link cells of the two layers. Intramuscular blood capillaries are rare and are found virtually only in the outer circular layer; their endothelial cells are joined by tight junctions. In the outer circular layer (but not in the other layers) there are two further cell types, fibroblasts and interstitial cells, which can be clearly distinguished from one another. The latter cells are intimately related to nerve bundles and are connected by gap junctions to some muscle cells.     

Effects of polyamines on contractility of guinea-pig gastric smooth muscle

This study was designed to investigate the effects of polyamines on mechanical contraction and voltage-dependent calcium current (VDCC) of guinea-pig gastric smooth muscle. Mechanical contraction and calcium channel current I(Ba) were recorded by isometric tension recording and whole-cell patch clamp technique. Spermine, spermidine and putrescine inhibited spontaneous contraction of the gastric smooth muscle in a concentration-dependent manner. Spermine (2 mM) reduced high K+ (50 mM)-induced contraction to 16+/-6.4% of the control (n=9), and significantly inhibited I(Ba) in a reversible manner (p<0.05; IC50=0.8 mM). Pre- and post-treatment of tissue with spermine (2-5 mM, n=10) also inhibited acetylcholine (10 microM)-induced phasic contraction to 5+/-6.4% of the control. Inhibitory effect of spermine on I(Ba) was observed at a wide range of test potentials of current/voltage (I/V) relationship (p<0.05), and steady-state activation of I(Ba) was shifted to the right by spermine (p<0.05). Spermidine and putrescine (1 mM each) also inhibited I(Ba) to 51+/-5.7% and 81+/-5.3% of the control, respectively. And putrescine (1 mM) inhibited I(Ba) at whole tested potentials (p<0.05) without significant change of kinetics (p<0.05). Finally, 5 mM putrescine also inhibited high K+-induced contraction to 53+/-7.1% of the control (n=4). These findings suggest that polyamines inhibit contractions of guinea-pig gastric smooth muscle via inhibition of VDCC.     

Time series analysis of guinea-pig taenia coli spontaneous activity

Summary Spontaneous tension changes of isolated strips of guinea-pig taenia coli were studied in using the time series analysis (evaluation of autocorrelation functions and power spectra). The results indicated three typical power spectral maxima with frequencies of 0.02–0.03 Hz, 0.06–0.07 Hz, and 0.1–0.14 Hz. These smooth muscle oscillation components were compared with the vascular autooscillations which previously were measured in the isolated rat kidney.This work was supported by Grant TAG-229 of Turkish Scientific and Technical Research Council (T.B.T.A.K.).     

吗啡对离体兔小肠平滑肌电变化及环肌和纵肌收缩活动的影响

本实验同时观察吗啡对离体兔十二指肠平滑肌电活动,肠腔内压变化以及纵肌收缩活动三方面的影响。结果显示:吗啡可使离体兔十二指肠节律性环肌收缩加强,纵肌收缩减弱,以及平滑肌峰电位幅度,数量和峰电位发生率增加。吗啡的小肠兴奋作用可被纳洛酮或阿托品阻断。吗啡对纵肌的抑制作用不被心得安阻断,但可被酚妥拉明减弱。实验结果表明吗啡对兔小肠环肌和纵肌作用相反,它兴奋环肌,抑制纵肌。吗啡是通过肠道阿片受体起作用的。乙酰胆碱参与了吗啡对小肠的作用。     

An effect of the electrogenic sodium pump on the membrane potential in beating guinea-pig atria

Summary The membrane potential of guinea-pig atria was measured in different media before, during and after electrical stimulation of various durations. The stimulus duration and frequency (3 pulses/sec) were kept constant.During short stimulation (<1 min) in Tyrode solution at 35°C the membrane potential depolarized first quickly and later on more slowly. Following cessation of the stimulus train the membrane potential repolarized to the resting value within 1–2 min.Prolonged stimulation (1–7 min) in Tyrode solution at 35°C likewise caused an initial depolarization of membrane potential. Thereafter, the membrane potential repolarized although stimulation continued. After the end of the stimulation period the membrane potential hyperpolarized beyond the resting potential for several minutes. Maximum hyperpolarization was achieved ca. 1 min after the end of the stimulus train.In Tyrode solution at 25°C both the repolarization of the membrane potential during long stimulation and the hyperpolarization after it were diminished. The same effect was observed in Na poor fluids, which contained only 50 or 33% of the Na concentrations in Tyrode solution.Digitoxigenine (3·10^–6 g/ml), when added to Tyrode solution at 35°C, also reduced the repolarization of membrane potential during, and the hyperpolarization after, a long stimulus train.Compared to the resting value the membrane resistance was essentially unchanged 1–3 min after a 2 min stimulation period.From these results it is concluded, that an active, electrogenic Na pump contributes to the membrane potential of beating guinea-pig auricles.     

Juxtaglomerular granules in subcellular fractions of guinea-pig kidney

Summary The preparation of a subcellular fraction of renin-containing juxtaglomerular granules of guinea-pig kidney is described. Two separate preparations had a 8.4 and 15 times higher pressor activity [3] per mg protein than the respective homogenate. Electron microscopy showed mitochondria, non-specific and specific juxtaglomerular granules in the granular fraction. It is concluded, that the concept of adult guinea-pig kidney as an agranular model for the investigation of production and release of renin has to be modified.We thank Dr. W. G. Forssmann for help and discussion.     

The action of lanthanum and D600 on the calcium exchange in the smooth muscle cells of the guinea-pig taenia coli

Summary The calcium distribution in smooth muscle cells of the taenia coli has been studied with a method based on the action of lanthanum ions. La³⁺-ions make it possible to separate the extracellular calcium from the cellular calcium by their high affinity for extracellular calcium binding sites and by their blocking action on the transmembrane calcium movements. Using this method the cellular calcium content and its exchangeable fraction have been determined. In spontaneously active tissues the exchange of the cellular calcium reaches a maximal value of 108 M/kg wet wt or 1/6 of the total cellular calcium, while in quiescent tissues (treated with D600) this maximal value is 80 M/kg wet wt.During K depolarization a large amount of extracellular calcium penetrates in the cellular compartment. This entry and the corresponding tension development are inhibited by D600.These results are interpreted by assuming that even during spike discharge the Ca-permeability of the membrane is very small and that this entering calcium could function as a trigger, releasing intracellularly localized calcium. This physiological mechanism should be distinguished from the important uptake of calcium occurring during K-depolarization.     

Serrated neoplasia of the gastro-intestinal tract

Serrated neoplasia of the gastro-intestinal tract have peculiar microscopic and molecular features that are still incompletely described. Some serrated polyps seem to be involved in a new carcinogenic pathway in the colon: the serrated neoplasia pathway, with hypermethylation of the cytosine-guanine dinucleotides, located in the promoter of some genes such as h-MLH1, BRAF and MGMT. The natural history of the serrated polyps and their risk for progression to malignancy are still unclear. There is no official guideline for the management of serrated polyps. The aim of this article is to describe the epidemiological, morphological, immunohistochemical and molecular characteristics of the serrated neoplasia of the gastrointestinal tract: hyperplastic polyps, "traditional" serrated adenomas, mixed hyperplastic and adenomatous polyps, sessile serrated adenomas, hyperplastic polyposis and serrated adenocarcinomas.     

The effects of CO2 and pH on the spontaneous activity of the taenia coli of guinea-pig

Summary Mechanical and electrical activity of the isolated guinea-pig taenia coli were recorded in bicarbonate-, Tris- or phosphate-buffered test solutions. In normal solution (pCO₂ 5%, pH 7.4), typical minute-rhythmical fluctuations of activity occurred, whereby activity was present for approximately 40% of the total time (active time), the other 60% being activity-free intervals. At constant extracellular pH, low CO₂ content increased active time, high CO₂ content reduced it. Extracellular alkalinization at constantpCO₂ also diminished active time, even in CO₂-free medium, whereas acidification raised it, sometimes causing continuous activity. At constant bicarbonate-buffer, changes of CO₂ content, i.e. accompanied by corresponding changes in pH, affected the active time much less than did CO₂ alterations in an isohydric medium. The test solutions had no major effect on frequency of synchronized spike discharges, in contrast to their actions on the minuterhythmical activity. Since CO₂ can pass through the cell membrane more easily than ions regulating intra- and extracellular pH, the observed effects are best explained by changes in the transmembrane pH-gradient. A drop in active time would be due to a relative intracellular acidification; continuous activity, on the other hand, due to an opposite change in transmembrane pH-gradient, i.e. a relative intracellular alkalinization.This work was supported by the Deutsche Forschungsgemeinschaft     

The role of the antigravity musculature during quiet standing in man

Summary The view that postural regulation is achieved by controlling the destabilising effects of gravity through myotatic reflex activity was examined using surface electromyography. Forty seconds of recordings were made of myograms from eighteen muscles in each of a sample of nine young adults. It was observed that antigravity muscular activity in standing is generally low and often absent, and that the myograms from the muscles of the right and left sides of the body differed appreciably, the two sides rarely working together. Some sudden and united bursts of antigravity muscle activity could be observed. These might well have been stretch reflex induced, but they were transient and rare. It is concluded that the view that postural control in quiet standing is continuously mediated in a simple way by stretch reflex mechanisms is probably not valid, and that other mechanisms for controlling posture remain to be identified.This work was carried out with the support of the Science Research Council     

Heat production in the gastro-intestinal tract of the dog

1. Mean temperature from the lumen of the dog duodenum was 0.6 degrees C hotter than aorta. Ileum, stomach and large intestine were slightly cooler but still about 0.5 degrees C hotter than aorta.2. Portal vein averaged 0.35 degrees C hotter than the aorta.3. From portal blood flow data and aortic-portal temperature differentials heat production was calculated for the 10 kg dog as 3.4 kcal/hr.Evidence is adduced to show in these experiments that the gastro-intestinal tract produced 60% more heat than the liver.Total splanchnic heat production was about 33% of the total bodily heat production.4. The following procedures were carried out: adrenergic neurone blockade, atropine administration, vagotomy, prior starvation, bowel sterilization. All were without effect. It was concluded that smooth muscle activity, active transport or microbiological activity were unlikely to be sufficient to account for the high level of heat production.5. It was suggested that mucosal activity was the most likely source of heat. The possible involvement of unidentified metabolic pathways was discussed but oxidative mechanisms alone were shown not to be sufficient explanation.6. Since the rectal temperature was not significantly different from aortic it was concluded that the rectum was metabolically inactive and usually passively assumed the temperature of its blood supply.     

Neuronal composition of the intramural ganglia of the gastro-intestinal tract

The neuronal composition of the intramural plexuses of the gastro-intestinal tract in cats was studied by luminescence microscopy. The intramural ganglia were found to contain three populations of neurons. The neurons of the first population showed no specific catecholamine fluorescence. Those of the second population had fluorescence of the perikaryon and processes. The perikarya of the third neuron population were not fluorescent but adrenergic synapses were seen on their surface. Intraperitoneal injection of exogenous noradrenalin (1 mg) led to an increase in the number of neurons of the third population with specific fluorescence. On this basis it was concluded that as well as parasympathetic intramural neurons the intramural ganglia of the gastro-intestinal tract also contain sympathetic cells, most of which exhibit specific fluorescence only after their mediator content has been artificially increased.     

Gastric fundic inhibition of sugar transport across the intestinal mucosa of guinea-pig

A low molecular weight peptide designated gastric fundic factor (GFF), extracted from porcine fundic mucosa and administered to the serosal surface of mucosal sheets from guinea-pig intestine, decreased the transport of luminal glucose across the sheets by up to 70%. The results show that gastric fundic inhibition of glucose absorption observed in different animal models in vivo can be reproduced in vitro, and suggest that the intestinal mucosa itself is the target for peptide hormone(s) released by the gastric fundic mucosa. Simultaneous transport of -aminoisobutyric acid, a nonmetabolisable amino acid, through the jejunal mucosa was unaffected as was paracellular permeation by inulin. However, amino acid transport was also reduced when GFF was administered to sheets of ileal mucosa. The intestinal mucosal sheet in vitro is a sensitive and convenient model with which to follow the purification of GFF to homogeneity.     

The macrophage population of the gastro-intestinal tract of the rat

The macrophage population of the gastro-intestinal tract of the rat was studied by using a set of three monoclonal antibodies (ED1, ED2 and ED3) directed against rat macrophages, an anti-Ia monoclonal antibody and by performing an acid phosphatase reaction. The lamina propria of the whole gastro-intestinal tract comprised quite high numbers of macrophages. This macrophage population was heterogeneous. The Ia-positivity and the acid phosphatase activity of the macrophages were higher in the intestines than in the stomach and esophagus. ED1-positive macrophages were also quite numerous in the intestines; their number was relatively low in the esophagus and stomach. ED2-positive macrophages were found equally dispersed along the gastro-intestinal tract; ED3-positive cells were hardly found. The functional implications of the present findings are discussed.     

Mechanical characteristics of chemically skinned guinea-pig taenia coli

Strips of intact and chemically skinned (Triton X-100) taenia coli were mounted for isometric and quick-release experiments at 23°C. Active force increased in repeated high-K⁺ induced contractures in the intact muscle. Stable maximal force was 313±24 mN/mm² (n=6). The skinned preparations activated by Ca²⁺, at 2 mM Mg²⁺, 3.2 mM MgATP and ionic strength 0.085 M, gave half maximal force atpCa=5.62±0.4 and a maximal force (63±8 mN/mm²) atpCa=4.5 (20–25 of the control K⁺-responses prior to skinning but about 60% of the first K⁺-response). Force-velocity relations were obtained from intact muscles and from the same muscles chemically skinned and activated at optimal Ca²⁺. Maximal shortening velocity (V _max) was unaltered in the skinned preparation compared to the intact muscle (0.138±0.011 vs 0.140±0.006 L/s) indicating similar kinetics of actomyosin interaction. In the intact muscle a decrease inV _max was found when the Ca²⁺ concentration was reduced. Calmodulin (1M) increased Ca²⁺ sensitivity (by about 0.6 log units) of the skinned preparation but at optimal Ca²⁺ caused no alteration in isometric force orV _max Apreliminary report of some of the results presented here was given at the Scandinavian Physiology Society Meeting in Århus, November 1981. Arner A, Hellstrand P (1982) Acta Physiol Scand (Abstract) 114: 38 A.     

缺氧内皮细胞培养液对肺动脉平滑肌细胞表型的影响

用细胞培养和形态定量分析方法观察缺氧对肺动脉平滑肌细胞表型的影响。结果显示，缺氧性内皮细胞条件培养液组肺动脉平滑肌细胞的二倍体细胞和α－ｓｍ－ａｃｔｉｎ含量均少于常氧性内皮细胞条件培养液组（Ｐ＜０．０５），尤以肌丝成份减少最明显；粗面内质网和线粒体却显著增多。而直接缺氧组与常氧组无明显差异。提示：缺氧可促使内皮细胞产生和释放某种促平滑肌细胞表型转化的物质或因子，从而改变了肺动脉管壁细胞之间的正常调控关系，导致平滑肌细胞肥大，合成细胞外基质增多。