Reduced cold-induced thermogenesis in familial human obesity

Summary It is well known that cold and diet-induced thermogenesis, which is mediated in small rodents by the hypothalamic-noradrenergic fibersbrown adipose tissue axis, is impaired in genetically obese mice. To test whether these adaptive mechanisms are also impaired in obese humans, 12 young males who were otherwise healthy (6 lean and 6 obese) were examined. The obese subjects had an early-onset type of obesity with a strong family history of it as well. Deep body temperature was measured by using a deep body thermometer furnished with three thermocouples. They were respectively placed on the sternum, on the interscapular area immediately under the neck (HIS), and on the 4th intercostal space (LIS) in order to study core temperature as well as heat production where brown adipose tissue could also be present in adults. Both lean and obese subjects were kept in a thermoneutral environment (28° C) until they reached a steady-state body temperature and then rapidly transferred into a cold room (6–8° C) where they remained up to 60 min. Body temperature decreased in both groups, but the decrease was more marked in the obese individuals on the sternum (P<0.01), on HIS (P<0.05) and on LIS (P<0.05) when compared to lean individuals. In conclusion, cold-induced thermogenesis is impaired in familial early-onset human obesity and in genetically obese mice.Abbreviations BAT brown adipose tissue - BMI body mass index - HIS high interscapular area - LIS low interscapular area     

Humoral factors and the sodium-potassium pump in low renin hypertension

Summary Recent studies suggest that sodium dependent low renin hypertension results in part from the release of a ouabain-like factor, perhaps natriuretic hormone, from the brain. This humoral factor inhibits Na⁺, K⁺-ATPase and hence the active pumping of sodium and potassium in the muscle cells of blood vessels and heart. The pump suppression causes increased contractile activity and hence increased arterial blood pressure. In the muscle cells of the blood vessels, the increased contractile activity appears to be related to membrane depolarization.     

Abnormal red-cell calcium pump in patients with idiopathic hypercalciuria

Idiopathic hypercalciuria is a common disorder whose inheritance suggests an enzyme abnormality in calcium transport. We measured calcium-magnesium-ATPase activity in erythrocytes from 38 patients (mean age [+/- SEM], 40 +/- 2.1 years) with idiopathic hypercalciuria (24-hour urinary calcium excretion greater than or equal to 0.1 mmol per kilogram of body weight) and a history of multiple calcium oxalate kidney stones. As compared with 41 healthy controls, the patients with hypercalciuria had increased erythrocyte-membrane calcium-magnesium-ATPase activity (64.2 +/- 2.19 vs. 51.6 +/- 1.91 nmol of ATP split per milligram per minute; P less than 0.01) and increased sodium-potassium pump activity (6866 +/- 233 vs. 6096 +/- 228 mumol of sodium per liter of red cells per hour; P less than 0.05). No significant difference between the two groups was found in erythrocyte sodium-potassium cotransport, sodium-lithium countertransport, or potassium content. In 66 patients with kidney stones (38 with hypercalciuria and 28 with normal calcium excretion), 24-hour urinary calcium excretion correlated with calcium-magnesium-ATPase activity (r = 0.46, P less than 0.001). Erythrocyte calcium-magnesium-ATPase activity remained unchanged in eight subjects studied after four months on a low-calcium diet. A study of 30 healthy families found significant correlations between mean values in parents and those in offspring for calcium-magnesium-ATPase (r = 0.68, P less than 0.001) and urinary calcium excretion (r = 0.45, P less than 0.02), with no significant correlations between parents with respect to these measures (r = 0.27 and r = 0.08, respectively). We conclude that abnormalities in erythrocyte calcium-magnesium-ATPase activity may represent an inherited defect in calcium transport related to the cause of idiopathic hypercalciuria.     

Reduced activity without hyperphagia contributes to obesity in Tubby mutant mice

The Tub gene was originally identified as a spontaneous mutation in C57Bl/6J mice, and associated with adult-onset obesity (Tub MUT mice). Although the original Tub MUT mouse was identified over 15 years ago, there have been few reports on the animal's food intake, body fat percentage or energy expenditure. In this study, we report food intake, body weight from 5-20 weeks, body fat, body temperature and three different measures of physical activity behavior. Tub MUT mice display reduced food intake, uncharacteristic of many obese mouse models, and reduced voluntary wheel running with normal home cage ambulatory behavior. We conclude that motivation for food and exercise is an underlying defect in TUB MUT mice.     

The interaction of lithium ions with the sodium-potassium pump in frog skeletal muscle.

1. The effects of external Li on Na and K efflux as well as those on K influx were studied in high Na muscles from Rana pipiens. 2. In the absence of external Ba, substitution of K-free Li for K-free Mg resulted in an increase of both Na and K efflux. The additional of ouabain produced an inhibition of Na efflux and at the same time a marked increase in the efflux of K. 3. K permeability was greatly reduced by adding 2 mM-Ba to the incubation solutions. Under these conditions, Li gave rise to a ouabain sensitive Na efflux which was 57% of that in the absence of Ba. On the other hand, the efflux of K was only slightly increased and was not affected further by ouabain. 4. The activation curves of Na efflux against the stimulating cation concentration in Na-free Mg-Ba Ringer followed a more or less hyperbolic function for both K and Li. While half-maximal activation was attained at higher concentrations of Li than of K, the maximal efflux in Li was smaller than in K. 5. The extra Na efflux produced by K was increased when Li was added to the media. This increment was not a simple additive effect and was independent of the Li concentration. In addition, at some concentrations Li increased the ouabain-sensitive K influx, whereas at others it reduced it. 6. Reversible changes in membrane permeability to monovalent cations were accomplished by incubating the muscles in the presence of Nystatin, 50 mug/ml. When internal K was reduced to values around 1-2 mumole/g (using Li as a replacement), thus minimizing the possibility of K leaking out of the cells, both Ko and Lio were able to promote a ouabain-sensitive extra efflux of Na. 7. The residual Na efflux in (K+Na)-free solutions was not affected by the removal of Ca from the media in either Mg or Li solutions, both in the absence and the presence of Ba. On the other hand, the values for the residual efflux were higher in Mg (0-00228 min-1) than in Li (0.00135 min-1). 8. These results fully support the notion that Li ions have a K-like activating action on the Na pump in muscles. In addition, they suggest that some other kind of interaction may exist between Li and the Na-K pump.     

Effects of adrenaline on excitation-induced stimulation of the sodium-potassium pump in rat skeletal muscle

Experiments were performed on isolated rat soleus and extensor digitorum longus (EDL) muscles of 4-week-old rats. In the soleus, direct electrical stimulation for 10 min induced a frequency-dependent increase in the ouabain-suppressible 86Rb+ uptake, which was maximal (+110%) at a frequency of 2 Hz. In the EDL this frequency only induced a 31% increase. A supramaximal concentration of adrenaline (10 mumol l-1) stimulated ouabain-suppressible 86Rb+ uptake by 80% and 27% in soleus and EDL, respectively. The combined effect of stimulation at 2 Hz and adrenaline was not significantly larger than each of the interventions alone in either of the muscles. The fractional loss of 22Na+ from soleus muscle was increased by around 50% by the exposure to adrenaline, electrical stimulation at 2 Hz or a combination of both. The effect of electrical stimulation on 22Na+ efflux was not prevented by addition of propranolol (1 or 10 mumol l-1). The results indicate that the stimulation of active Na+-K+ transport induced by adrenaline or electrical stimulation is much more pronounced in soleus (slow-twitch) muscle than in EDL (fast-twitch) muscle. Since it has been suggested that an accumulation of K+ ions in the extracellular space may play a role in the development of fatigue (Bigland-Ritchie 1984), our findings might be related to the fact that slow-twitch muscles have a much higher resistance to fatigue than fast-twitch muscles (Burke et al. 1971).     

Reduced expression of SM22 is correlated with low autophagy activity in human colorectal cancer

Colorectal cancer (CRC) is a common malignancy with a high incidence and mortality rate. Recent studies have pointed to deregulation of autophagy as a novel pathogenesis of human malignancy. SM22 is considered as a tumor suppressor. The aim of the present study was to evaluate the correlation of the SM22 expression level with the autophagy activity and the clinical characteristics in human CRC tissues. The expressions of SM22 and p62, a biomarker of autophagy activity, in paired tumor and adjacent non-tumor tissues from 43 patients with colorectal cancer were detected by western blot and immunohistochemical staining, respectively. The results showed that the SM22 level decreased significantly in 81.4% CRC tissues, while the expression of p62 increased in 79.1% cases. There was a negative correlation between p62 and SM22 expressions in colorectal cancer tissues (p = 0.004). Similarly, the negative correlation between SM22 and p62 was verified in human CRC cell lines. The data suggest that the autophagy activity decreased in human CRC, which was associated with reduction in SM22 expression. However, the expression of SM22 was not associated with the gender, tumor site and Duke's stage of the patients. In conclusion, our findings suggest that the disruption of SM22 may be involved in tumorigenesis in CRC. The autophagic activity may be suppressed in human CRC, and SM22 may act as a positive regulator in the processes of autophagy.     

Reduced GABA transaminase activity in the Huntington's disease putamen

GABA transaminase activity is reduced in autopsied putamen samples from patients dying with Huntington's disease. Its activity is also reduced in the striatum of rats previously lesioned with kainic acid. In both cases, the reduction in GABA transaminase activity is comparable with the reduction in glutamate decarboxylase activity, supporting the suspected localization of this enzyme to GABA neurones within the basal ganglia.     

Reduced activity in rats with induced phenylketonuria

Hypoactivity was observed in the open field performance of 28 rats fed a diet containing 3% excess L-phenylalanine and .12% p-chlorophenylalanine between 21–51 days of age (PKU group) compared to both pair-fed and ad lib control groups. Open field testing was conducted 4–11 days following termination of the phenylalanine, p-chlorophenylalanine diet. While on the diet serum phenylalanine levels of the PKU group ranged between 16.6–38.0 mg%. Twenty-four to 48 hours following termination of the PKU diet serum phenylalanine levels had returned to normal (i.e., 2–10 days prior to open field testing). The reduced open field activity of the PKU group is not attributable to differences in food consumption or weight at the time of testing. Hypoactivity is consistent with previous investigations administering chronic doses of phenylalanine, but employing different induction techniques, treatment durations, and activity measures.     

Distribution of sodium-potassium ATPase in the rat testis and epididymis

Sodium-potassium ATPase (Na⁺ K⁺-ATPase) is a ubiquitous plasma membrane enzyme which uses the hydrolysis of ATP to regulate cellular Na⁺ and K⁺ levels and fluid volume. This ion pumping action is also thought to be involved in fluid movement across certain epithelia. There are several different genes for this enzyme, some of which are tissue specific. Using an antibody specific for the catalytic subunit of canine kidney Na⁺ K⁺-ATPase, we have localized immunoreactivity in the seminiferous and epididymal epithelium of rats of various ages. There was no specific staining of 10-day-old rat testis. Faint staining was detected at 13 days and appeared to be associated with the borders of Sertoli cells. At 16 days prominent apical and lateral staining but no basal staining of Sertoli cell membranes was observed. This type of distribution continued until spermatids were present in the epithelium. In the adult rat testis, specific staining was detected in Sertoli cell crypts associated with elongating spermatids, and on the apical and lateral Sertoli cell membrane. In some instances immunoreactivity was concentrated at presumed sites of junctional specializations. In the excurrent ducts of immature and mature rats, Na⁺ K⁺-ATPase staining was heavy in the efferent ducts and somewhat lighter in the epididymis. In all regions, the staining was basolateral although there were variations in intensity among the different parts of the epididymis. These results show (1) that rat testis and epididymal Na⁺ K⁺-ATPase share some immunological determinants with the canine enzyme; (2) that the epididymal enzyme is located in the conventional basolateral position; and (3) that the distribution of Sertoli cell Na⁺ K⁺-ATPase is probably apical and lateral rather than basal.     

Reduced apoptosis rates in human schwannomas

Schwannomas, tumors originating from Schwann cells, represent a frequent neurological tumor and can occur both in a genetic disorder called neurofibromatosis type 2 (NF2) and sporadically. In both cases the genetic background is identical as all schwannomas are caused by biallelic mutations in the tumor suppressor gene NF2 coding for merlin. Mutations in this gene have also been found to be responsible for 50% to 60% of spontaneous and 100% of the NF2 associated meningiomas. The NF2 gene product, merlin, links transmembrane proteins to the cytoskeleton and is involved in intracellular signaling processes. It has previously been shown that reexpression of wild-type merlin in primary human schwannoma cells leads to an increase in the number of apoptotic cells. Here, we report in vivo and in vitro evidence that the basal apoptosis rate of primary human schwannoma cells is reduced in comparison to that of normal Schwann cells, supporting the idea that in this benign tumor type, apoptosis has a role in tumorigenesis.     

Undershoots of intracellular sodium and the strength of contraction when the sodium-potassium pump of isolated sheep Purkinje fibres is reactivated by potassium.

We have recorded changes of membrane current, intracellular Na+ activity (aiNa), intracellular pH (pHi) and the strength of contraction in voltage-clamped sheep Purkinje fibres during and after inhibition of the Na(+)-K+ pump. The pump was inhibited by the removal of K+ from the bathing solution and this resulted in a rise in aiNa. On return of K+ to the bathing medium to reactivate the Na(+)-K+ pump there was a fall of aiNa to below its control value after which aiNa slowly returned to its control value over the next 20 min. This 'undershoot' of aiNa was seen in 69% of contracting fibres and 78% of quiescent fibres, and the mean (+/- S.D.) values of the undershoot in contracting and quiescent fibres were 0.66 +/- 0.15 and 0.9 +/- 0.35 mM, respectively. The undershoot of aiNa was observed regardless of whether the Na(+)-K+ pump was reactivated with Rb+ or K+. It was not voltage dependent over the potential range studied (-95 to -45 mV) and was not accompanied by a change of intracellular pH. The undershoot of aiNa could be the result of a long-lasting increase in Na+ efflux or a long-lasting decrease in Na+ influx. Zero [K+]o resulted in the loss of one Na+ current, the pacemaker current i(f), but when K+ was returned to the bathing medium i(f) recovered rapidly and is therefore unlikely to be responsible for the long-lasting undershoot of aiNa. This conclusion was confirmed by the use of Cs+: although Cs+ blocked i(f), it did not block the undershoot of aiNa. The undershoot of aiNa was accompanied by (and, via Na(+)-Ca2+ exchange, was presumably the cause of) an undershoot of the force of contraction. Undershoots are not only seen after reactivation of the Na(+)-K+ pump: in a variety of different preparations, similar undershoots in aiNa and twitch force have been reported after a decrease in the frequency of stimulation. The undershoot of aiNa may be the result of novel feedback mechanism for the control of aiNa: the control of Na+ influx by aiNa.     

Reduced rate of fat oxidation: A metabolic pathway to obesity in the developing nations

The purpose of this article is to document the metabolic and environmental factors associated with the increased frequency of obesity in the developing nations. While the prevalence of obesity in the developed countries is caused by the increased consumption of calorie‐dense foods, in the developing nations, because obesity coexists with undernutrition, additional factors are necessary to account for it. The evidence suggests that an important contributing factor for obesity in the developing nations is a reduced fat oxidation and increased metabolism of carbohydrate that has been brought about by the chronic undernutrition experienced during prenatal and postnatal growth. This shift toward a preferential metabolic use of carbohydrate rather than of fat results in an increased deposition of body fat. This tendency, along with the general decrease of energy expenditure in physical activity associated with urbanization, and the culturally mediated acceptance of fatness leads to obesity among populations from the developing nations. A joint effect of these factors is that in the developing nations obesity is associated with short stature resulting from developmental undernutrition, while in the developed countries obesity is associated with tall stature. It is hoped that future research will address the mechanisms whereby undernutrition increases the tendency toward obesity. Understanding how to modify fat oxidation could affect our ability to prevent weight gain among undernourished populations of the developing nations. Therefore, future research on the interaction of undernutrition and the development of obesity is of prime importance for anthropology concerned with the origins of human variability. Am. J. Hum. Biol. 15:522–532, 2003. © 2003 Wiley‐Liss, Inc.     

The venous pump of the human foot

Pressures in the flexor digitorum muscle, posterior tibial and anterior tibial muscles and subcutaneous pressure in the lower leg were recorded in 18 volunteers with a non-infusion technique. The venous plexus of the sole of the foot was compressed by a pneumatic foot pump. Activation of this device creates oscillations of intramuscular and subcutaneous interstitial fluid hydrostatic pressure in the lower leg. The mechanism for this is explained by intermittent passive muscle stretch. The interstitial fluid pressure decreased following active muscle contractions during venous stasis of the limb, but not following activation of the pneumatic pump. Although the pneumatic foot pump may on theoretical grounds be useful in early treatment of postoperative and post-traumatic oedema of the leg, complementary studies are necessary to establish its effectiveness.     

Contribution of immunochemical methods to the study of human red-cell membrane proteins (author's transl)

Together with the classical technics of biochemical analysis, immunological methods have led to differentiate, characterize the main red-cell membrane. proteins and to better understand their organization. Immunological methods were particularly involved in the study of: 1) the membrane skeletal proteins, specially spectrin which localization in the membrane, structure and functions have been specified; 2) the principal integral proteins, glycophorin and protein band 3, the transmembrane orientation of which has been corroborated by topographic immunological mapping of their cytoplasmic domain; 3) the anchor chain protein, linking membrane skeleton to the transmembrane proteins. These methods could further help to a better understanding of the membrane structure. Two kinds of work can be considered using monoclonal antibodies provided by the hybridoma method : 1) the purification by immunoadsorbent technics, of quantitatively minor membrane proteins, would allow to study their structure and functions ; 2) an immunological mapping with monoclonal antibodies specific against each of the skeleton proteins, of membrane preparations observed in electronic microscopy, would permit to visualize the real architecture of these different proteins in the red-cell membrane