The mechanism of insulin stimulation of (Na+,K+)-ATPase transport activity in muscle

Since the mechanism underlying the insulin stimulation of (Na+,K+)-ATPase transport activity observed in multiple tissues has remained undetermined, we have examined (Na+,K+)-ATPase transport activity (ouabain-sensitive 86Rb+ uptake) and Na+/H+ exchange transport (amiloride-sensitive 22Na+ influx) in differentiated BC3H-1 cultured myocytes as a model of insulin action in muscle. The active uptake of 86Rb+ was sensitive to physiological insulin concentrations (1 nM), yielding a maximum increase of 60% without any change in 86Rb+ permeability. In order to determine the mechanism of insulin stimulation of (Na+,K+)-ATPase activity, we demonstrated that insulin also stimulates passive 22Na+ influx by Na+/H+ exchange transport (maximal 200% increase) and an 80% increase in intracellular Na+ concentration with an identical time course and dose-response curve as insulin-stimulated (Na+,K+)-ATPase transport activity. Incubation of the cells with high [Na+] (195 mM) significantly potentiated insulin stimulation of ouabain-inhibitable 86Rb+ uptake. The ionophore monensin, which also promotes passive Na+ entry into BC3H-1 cells, mimics the insulin stimulation of ouabain-inhibitable 86Rb+ uptake. In contrast, incubation with amiloride or low [Na+] (10 mM), both of which inhibit Na+/H+ exchange transport, abolished the insulin stimulation of (Na+,K+)-ATPase transport activity. Furthermore, each of these insulin-stimulated transport activities displayed a similar sensitivity to amiloride. These results indicate that insulin stimulates a large increase in Na+/H+ exchange transport and that the resulting Na+ influx increases the intracellular Na+ concentration, thus activating the internal Na+ transport sites of the (Na+,K+)-ATPase. This Na+ influx is, therefore, the mediator of the insulin-induced stimulation of membrane (Na+,K+)-ATPase transport activity classically observed in muscle.     

Temporal Distribution of [3H]-Imipramine Binding in Rat Brain Regions is Not Changed by Chronic Methamphetamine

Specific binding of [³H]-imipramine in the rat suprachiasmatic nuclei, occipital cortex and caudate putamen underwent significant and replicable changes throughout 24 hr under a light-dark cycle or under constant conditions. Daily variations were also found in the medial and dorsal raphe nuclei and the lateral hypothalamus. Methamphetamine, a psychoactive drug with marked effect on circadian rhythms in physiological and hormonal parameters and adrenergic receptors, did not have any significant effect on imipramine binding rhythms in eight discrete brain regions. Thus a drug known to reduce serotoninergic neurotransmission did not change characteristics of the modulatory binding site related to serotonin uptake.     

Presence of glyoxalase II in mitochondria from spinach leaves: comparison with the enzyme from cytosol

Glyoxalase II has been purified from cytosol and mitochondria of spinach leaves. Electrophoresis and isoelectric focussing have resolved cytosolic and mitochondrial glyoxalase II in multiple forms: pl 5.3, 5.8 and 6.2 (cytosol) and pl 4.8 (mitochondria). The enzyme of both localizations is a monomer showing a relative molecular mass of about 26 kDa. The values of kinetic constants using several glutathione thiolesters as substrates, are similar for the enzymes from cytosol and mitochondria. These results extend also to plant the presence in mitochondria of peculiar forms of glyoxalase II, likewise recently demonstrated in mammalians.     

Production of amylase(s) by Schwanniomyces castellii and Endomycopsis fibuligera

Schwanniomyces castellii and Endomycopsis fibuligera Produced extracellular amylase(s) when grown on various carbon sources and at different pH values. Both yeast species showed significant amylase synthesis in the presence of either maltose or soluble starch. On the other substrates tested (glucose, cellobiose, sucrose, trehalose, melezitose, raffinose, ethanol, glycerol) differences were found regarding growth and amylase production. Free glucose in the culture medium apparently inhibited enzyme synthesis. The pH range allowing maximal growth and amylase production was 4.5–6.0 for E. fibuligera and 5.5–7.0 for S. castellii.     

Trisomy 6p22→6pter due to familial t(6;13)(p22;q34 or 33) translocation

Summary 235 cases of Down's syndrome were ascertained in a 10-year study of Down's syndrome in Western Australia. Although cytogenetic studies performed on 222 subjects confirmed that 95% of cases were trisomic due to nondisjunction, 4% were trisomic due to translocation, and 1% were mosaic, the ratio of inherited/sporadic translocations differed from that usually reported. Comparison of the results with those of an earlier Australian survey of Down's syndrome demonstrated a real fall in the incidence of Down's syndrome in Australia but no significant change in maternal age-specific incidences.     

A case of true hermaphroditism with 45X/46XY mosaicism

Summary The authors describe a case of true hermaphroditism of mainly female phenotype, ambiguous external genitalia, and ovotestis. The cytogenetic studies revealed 45X/46XY mosaicism and an absence of Barr bodies.     

Laying characteristics of one- and two-year old pheasants (Phasianus colchicus, L.)

The aim ofthe study was to assess laying traits, the weight of eggs and characters ofthe laying rhythm of pheasants in the first and second years of reproduction. Pheasants (10 cockerels and 50 hens) were kept in aviaries. Daily, individual control of laying was performed beginning with the day of the first laying and ending with the last egg. The following parameters were evaluated: age at first laying, length of the laying period, number of laid eggs and the average weight of the egg in the 8th week of laying. The laying rhythm was also assessed and comprised: the number of egg clutches, the number of eggs in a clutch, the number of eggs in the longest clutch, the number of intervals, the length of intervals and the longest interval between clutches. During the first period of reproduction, in comparison with the second, pheasants laid slightly more eggs of similar average weight. The first laying period was longer than the second and was characterised by a greater number of egg clutches and greater number of intervals between clutches. The greatest number of eggs was laid in 10-egg and longer clutches, although the l-egg clutches were the most numerous. A positive correlation was found between the number of eggs and the number of clutches, the greatest number of eggs in a clutch and the number of intervals between clutches. The similar values of the reproductive characters of one- and two-year old pheasants point to the possibility of longer utilization of these birds than only for one laying period. On the other hand, the considerable variability between the experimental hens with regard to the number and the length of egg clutches, as well as the intervals between them, indicate the possibility to carry out selection taking into account traits characterising the laying rhythm.     

On the mechanism of drug-induced acceleration of phospholipid translocation in the human erythrocyte membrane

Small amphiphilic compounds (M(r)<200 Da) such as anaesthetics and hexane derivatives with different polar groups produced a concentration-dependent acceleration of the slow passive transbilayer movement of NBD-labelled phosphatidylcholine in the human erythrocyte membrane. Above a threshold concentration characteristic for each compound, the flip rate gradually increased at increasing concentrations in the medium. For compound concentrations required to produce a defined flip acceleration, corresponding membrane concentrations were estimated using reported octanol/water partition coefficients. The effective threshold membrane concentrations (50-150 mmol l(-1)) varied in the order: hexylamine>isoflurane=hexanoic acid>hexanol=chloroform>hexanethiol=1,1,2,2-tetrachloroethane>chlorohexane. Apolar hexane, which mainly distributes in the apolar membrane core, was much less effective and supersaturating concentrations were required to enhance flip. Localization of the drug at the lipid-water interface seems to be required for flip acceleration. Such a localization may increase the lateral pressure in this region and the bilayer curvature stress with concomitant decrease of order and rigidity at the interface. This unspecific bilayer perturbation is proposed to enhance the probability of formation of hydrophobic defects in the bilayer, facilitating penetration of the polar head group of the phospholipid into the apolar membrane core.     

Increased acetylcholinesterase activities in specimens of Sparus auratus exposed to sublethal copper concentrations

The present study looks at possible changes in the activity of acetylcholinesterase (AChE) in tissues (brain and white muscle) of the Mediterranean bony fish Sparus auratus after a 20 days exposure to sublethal concentrations (0.1 or 0.5 ppm) of copper in the marine water and on control untreated animals. The trials also included measurements of Cu concentration in the tissues to evaluate possible metal accumulation. Moreover, sedimentation analysis as well as V(max) and K(m) determination were carried out in tissue extracts of Cu-exposed or control animals. V(max) and K(m) were also determined with or without addition of Cu(2+) in the assay. No Cu accumulation occurred in brain and muscle after Cu exposure. AChE showed in both tissues a molecular polymorphism with putative globular (G) and asymmetric (A) forms. Cu exposition led to an increased specific activity and improved catalytic efficiency of AChE in brain and muscle, seemingly regarding G forms. The increase in catalytic efficiency also resulted from the in vitro assay with tissue extracts and Cu(2+) addition. The higher AChE activity and catalytic efficiency in both tissues after Cu exposition and without metal accumulation, suggests an increase of free Cu aliquot into the cells, likely due to mechanisms of metal homeostasis.     

Increase of Cerebral Phosphocreatine in Normal Rats after Intracerebroventricular Administration of Creatine

Intracerebroventricular (ICV) administration of creatine increased cerebral phosphocreatine in normal rats by 67%, the highest increase so far reported in an in vivo model. We used osmotic minipumps (Alzet, Palo Alto, CA, USA) to administer creatine, 0.5mM, to the lateral ventricle at the rate of 10 l/h for 3 days. Brain phosphocreatine in saline-treated controls was 33 ± 17 M/g protein (mean ± SD, N = 9). In creatine-treated rats (0.5 mM for 3 days) such content was 55 ± 17 M/g protein (mean ± SD, N = 7). This difference is statistically significant (p = 0.02, t-test). The increase we found in cerebral phosphocreatine is of an order of magnitude comparable to the increase previously found in in vitro experiments, and may be effective in protecting brain tissue from ischemic damage.