Relation between extracellular [K+], membrane potential and contraction in rat soleus muscle: modulation by the Na+-K+ pump

An increased extracellular K⁺ concentration ([K⁺]₀) is thought to cause muscle fatigue. We studied the effects of increasing [K⁺]₀ from 4 mM to 8–14 mM on tetanic contractions in isolated bundles of fibres and whole soleus muscles from the rat. Whereas there was little depression of force at a [K⁺]₀ of 8–9 mM, a further small increase in [K⁺]₀ to 11–14 mM resulted in a large reduction of force. Tetanus depression at 11 mM [K⁺]_o was increased when using weaker stimulation pulses and decreased with stronger pulses. Whereas the tetanic force/resting membrane potential (E _M) relation showed only moderate force depression with depolarization from –74 to –62 mV, a large reduction of force occurred whenE _M fell to –53 mV. The implications of these relations to fatigue are discussed. Partial inhibition of the Na⁺-K⁺ pump with ouabain (10^–6 M) caused additional force loss at 11 mM [K⁺]₀. Salbutamol, insulin, or calcitonin gene-related peptide all stimulated the Na⁺-K⁺ pump in muscles exposed to 11 mM [K⁺ ₀] and induced an average 26–33% recovery of tetanic force. When using stimulation pulses of 0.1 ms, instead of the standard 1.0-ms pulses, force recovery with these agents was 41–44% which was significantly greater (P < 0.025). Only salbutamol caused any recovery ofE _M (1.3 mV). The observations suggest that the increased Na⁺ concentration difference across the sarcolemma, following Na⁺-K⁺ pump stimulation, has an important role in restoring excitability and force.     

Interepithelial cells of the oral mucosa in mice

Summary Non-epithelial mesenchymal and neuroectodermal cells occur between the keratinocytes in the stratified squamous epithelium of the oral mucosa. These cells cannot be classified adequately by light microscopy. In the present study the oral mucosa of the lip, cheek and tongue of 50 mice were studied by light and electron microscopy. 3,025 mononuclear interepithelial cells were documented and analysed.Monocytogenic macrophages, plasma cells and mast cells were not found interepithelially and cannot be regarded as a regular constituent of the epithelium. Only a few neuroectodermal cells — in mice these are exclusively Merkel cells, with no melanocytes — were localized in the epithelium. The majority of the interepithelial cell population is made up of lymphocytes (22.8%) and Langerhans cells (56.8%). They are an integral constituent of the epithelium. Lymphocytes with rounded and indented nuclei can be identified. The larger and dendritic Langerhans cells are a specific cell of squamous epithelium and also occur in the oral mucosa. Not all cells which feature the cytological characteristics of Langerhans cells contain Langerhans or Birbeck granules. Accordingly these granules cannot be considered an exclusive identification characteristic. Two types of Langerhans cells can be differentiated. 80.9% have the more or less typical appearance known from the epidermis and were termed macrophagocytoid Langerhans cells. The nuclei are irregularly indented and moderately heterochromatic. 19.1% possessed conspicuous large, spherical, euchromatic nuclei and an electron-lucent cytoplasm. These were termed reticuloid Langerhans cells. About 20% of the interepithelial cell population could not be identified, neither as typical lymphocytes nor as Langerhans cells. These were small to medium sized cells with deeply indented cerebriform strongly heterochromatic nuclei. They are similar to the Sézary cells or mycosis fungoides cells of epidermotropic human T-cell lymphomas. The lymphocytic nature of these cells has been confirmed. It seems likely that differentiation of lymphocytes to cerebriform cells occurs within the epithelium. It is further discussed whether cerebriform cells are precursors of Langerhans cells, a conclusion suggested morphologically by transitional forms. This would imply that Langerhans cells originate from lymphocytes, and that the cerebriform cell is an intermediate step of differentiation. The microenvironment of the squamous epithelium may play a role in the process of differentiation, which could explain the epitheliotropy of lymphocytes. The possibility is considered that Langerhans cells and interdigitating reticulum cells of the T-cell area of lymph nodes are identical. The close functional cooperation of Langerhans cells, lymphocytes, and interdigitating reticulum cells in immunological defenses against external antigens is discussed.The authors wish to express their sincere appreciation to Miss P. Starck and Miss I. Brandt for invaluable technical assistance in this project.     

妊高征患者淋巴细胞β_2－肾上腺素能受体结合量改变及与新生儿体重关系的研究

应用放射配体结合分析，测定４０例正常晚期妊娠妇女及４０例妊高征妇女外周血淋巴细胞β_２－肾上腺素能受体（β_２－ＡＲ）结合量，并测定两组妇女分娩的新生儿体重。结果为：１．正常晚期妊娠妇女外周淋巴细胞β_２－ＡＲ结合量明显降低，妊高征妇女β_２－ＡＲ结合量降低更显著；２．妊高征孕妇组的新生儿出生体重明显低于正常妊娠组的新生儿体重；３．孕妇β_２－ＡＲ结合量与新生儿出生体重呈明显正相关，提示好高征与机体β_２－ＡＲ结合量下降有关，β_２－ＡＲ改变影响胎儿生长发育。     

Celiac vagotomy attenuates the ingestive responses to epinephrine and hypertonic saline but not insulin, 2-deoxy-D-glucose, or polyethylene glycol

The ingestive responses of rats given celiac vagotomy (C), combined celiac and hepatic vagotomy (CH), or low total vagotomy (removal of all tissue from around the esophagus, stomach and duodenum; LT) were compared with sham operated controls (S) in a series of regulatory challenges. The vagotomized groups responded normally to 2-deoxy-D-glucose (2DG; 125, 250, 500 mg/kg, IP), insulin (4, 8, 12 U/kg, IP), and polyethylene glycol (10 ml/kg: 30% w/v, SC), but displayed attenuated responses to epinephrine (40, 80, 120 micrograms/kg, IP) and hypertonic saline (10 ml/kg: 0.25, 0.5, 1.0 M, IP). These results can be interpreted as evidence that the celiac vagus carries a major component of hepatic afferent innervation. Additionally, when considered with other findings they suggest that whereas the anorectic activity of epinephrine is mostly confined to the liver, 2DG hyperphagia involves stimulation of a wider population of peripheral metabolic receptors.     

纳曲酮对移植排异反应的抑制作用

以小鼠心肌组织异位移植和混合淋巴细胞反应为整体和离体模型，观察了阿片受体阻断剂纳曲酮对移植排异反应的影响。结果显示：给动物从术前开始腹腔注射纳曲酮共１０天（每日二次，每次５ｍｇ／ｋｇ）可明显延长移植心肌组织的存活时间；加入纳曲酮（１０－４～１０－８ｍｏｌ／Ｌ）对混合淋巴细胞反应有抑制作用并呈量效关系。同时还观察到，给正常小鼠腹腔注射纳曲酮３天以上，可引起动物脾细胞由ＣｏｎＡ诱导的淋巴细胞转化反应受抑制。以上结果说明纳曲酮可抑制移植排异反应，此作用有可能是通过阻断内源性阿片肽所致。     

Diet selection and metabolic fuels in three models of diabetes mellitus

Dietary self-selection and circulating metabolic fuels (glucose, free fatty acids, ketones) were examined in three forms of experimental diabetes mellitus in rats: pancreatectomy and streptozotocin treatment in adult and neonatal rats. Changes in diet selection resulting from insulin replacement also were examined. Differences were found in diet selection and circulating metabolic fuels between these types of diabetes. Mildly diabetic rats selected large amounts of fat while more severely diabetic rats primarily selected protein. Insulin treatment enhanced carbohydrate intake of diabetic rats and nearly normalized diet selection and circulating metabolic fuels. All diabetic groups exhibited severe glucose intolerance. These results support the observations of the beneficial effects of low-carbohydrate diets, question the generality of the use of high-fat diets, and suggest a more important role for high-protein diets in energy regulation in severely diabetic rats.     

Effect of training on hormonal responses to exercise in competitive swimmers

Summary The effects of 9 weeks of training on responses of plasma hormones to swimming were studied in eight competitive swimmers who had not trained for several months. Two types of swimming tests were used: (1) 200 yd, a high intensity, exhausting type of exercise in which maximal effort was required both before and after training, and (2) 1000 yd, a pace type of exercise in which subjects swam as fast as possible prior to training and at the same rate after training. Plasma levels of glucagon increased and of insulin decreased during 1000 yd of swimming, but were not altered by 200 yd of swimming. No training effects were apparent in responses of plasma insulin and glucagon to these short-term, high intensity exercise tests. During the 1000 yd swim, plasma adrenaline was 0.8 ng/ml before vs. 0.1 ng/ml after training. Plasma noradrenaline response decreased from 3.4 to 1.2 ng/ml as a result of training. In the 200 yd swim, adrenaline, but not noradrenaline, was lower after training.R. C. Hickson and R. K. Conlee were postdoctoral research trainees supported by NIH Training Grant AM-05341.J. M. Hagberg was a postdoctoral research trainee supported by NIH Training Grant HL-07081.     

Dose-response relationship for a positive inotropic effect of insulin on isolated papillary muscle

Summary Beneficial effect of glucose and insulin on the myocardium are still a matter of discussion. The influence of insulin on isometric force of contraction of right ventricular papillary muscles of guinea pigs war studied. The papillary muscles were mounted vertically in a 95% O₂, 5% CO₂ modified Krebs-Hensuleit solution (31.5° C, 5.5 mM glucose) and stimulated 1/s. A positive inotropic effect of insulin was dedectable at a concentration of 5×10^–4 IU/ml insulin, was half maximal (52% above controle force of contraction) at 8×10^–3 IU/ml and maximal at 10^–1 IU/ml. The maximal positive inotropic effect was observed 4.7±0.6 min after addition of insulin. After the maximum there was a decrease to a steady state level of 109.8±8.5% of control (p<0.05) in 14.6±1.3 min. Higher glucose (16.5 mM) only shifted the half maximal positive inotropic effect to 5.5×10^–3 IU/ml insulin (n.s.). Inhibition of glycolysis with hypoxia or jodoacetate (5×10^–5 M) did not prevent the positive inotropic effect as known as 75% of control force was retained. When glucose transport was blocked with phlorizin (5×10^–3 M) or phloritin (5×10^–4 M) no positive inotropic action of insulin was observed. Therefore we conclude that the positive inotropic effect of insulin in isolated papillary muscles is mediated by inhanced glucose transport.     

Cell signalling-mediating insulin increase of mRNA expression for cationic amino acid transporters-1 and -2 and membrane hyperpolarization in human umbilical vein endothelial cells

Insulin induces vasodilatation in human subjects and increases l-arginine transport and NO synthesis in human umbilical vein endothelial cells (HUVEC). Cell signalling events associated with insulin effects on activity and mRNA expression of the human cationic amino acid transporters 1 (hCAT-1) and 2B (hCAT-2B) are unknown. l-Arginine transport and eNOS activity were determined in HUVEC exposed to insulin. mRNA levels for hCAT-1, hCAT-2B and eNOS were quantitated by real time RT-PCR and endothelial NO synthase (eNOS) protein was identified by Western blot analysis. Intracellular Ca²⁺, l-arginine and l-citrulline levels, l-[³H]citrulline formation from l-[³H]arginine, cGMP formation, nitrite level, ATP release and membrane potential were determined. Insulin increased l-arginine transport and the mRNA levels for hCAT-1 and hCAT-2B and eNOS expression and activity. Insulin also induced membrane hyperpolarization and increased intracellular Ca²⁺, l-[³H]citrulline, cGMP and nitrite formation. Insulin-mediated stimulation of the l-arginine/NO pathway is thus associated with increased hCAT-1 and hCAT-2B mRNA, and eNOS expression, via mechanisms involving membrane hyperpolarization, mitogen-activated protein kinases p42 and p44, phosphatidylinositol 3-kinase, NO and protein kinase C. We have characterized a cell signalling pathway by which hyperinsulinaemia could lead to vasodilatation in human subjects, and which could have implications in patients in whom plasma insulin levels are altered, such as in diabetes mellitus.     

Estradiol and insulin: independent effects on eating and body weight in rats.

The effects of ovariectomy and estradiol replacement were determined in streptozotocin-diabetic female rats maintained on daily injections of protamine zinc insulin. Similar changes in food intake and body weight in these animals and in nondiabetic control animals indicate that the effects of estradiol on these measures are probably not dependent on changes in pancreatic insulin secretion. Acute and chronic insulin challenges in ovariectomized rats maintained on estradiol benzoate, nafoxidine or oil were also examined. The effects of insulin were not attenuated by prior estrogen conditioning, and there was no evidence of insulin resistance. These experiments suggest that the effects of estradiol on body weight and food intake in female rats are not dependent upon altered insulin levels nor attenuation of the effects of insulin. Estradiol may exert its influence on eating and body weight via separate and possibly more direct pathways. The data also are consistent with the suggestion that ovariectomy-induced and hypothalamic obesities are separate phenomena.