Light sensitivity of the ciliate Tetrahymena vorax induced by the fluorescent dye acridine orange

The ciliate Tetrahymena vorax is normally insensitive to light. However, after uptake of acridine orange, blue light evokes instant backward swimming. The dye accumulates mainly in posterior vacuoles, with half-maximal uptake after 1 min. Illumination for 10 s induced a depolarisation of approximately 15 mV lasting less than 2 s, followed by a sustained hyperpolarisation of approximately 20 mV. Deciliated cells displayed a similar response. The hyperpolarisation was linked to reduced membrane resistance, showed a reversal potential of approximately −55 mV and was blocked by 1 mmol l⁻¹ TEA. The rate of rise of electrically evoked Ca²⁺-spikes was reduced during the hyperpolarisation, which is compatible with elevated cytosolic Ca²⁺ concentration. This suggests that the hyperpolarisation may be caused by activation of Ca²⁺-sensitive K⁺ channels. The depolarisation was abolished in Ca²⁺-free medium, whereas the hyperpolarisation was unaffected. Illumination for 2 s, or prolonged stimulation restricted to the anterior part of the cell, induced depolarisation only. Illumination of the posterior part caused delayed hyperpolarisation with no preceding depolarisation. We conclude that the induced backward swimming is associated with Ca²⁺ influx through anterior channels, while Ca²⁺ released from intracellular stores activates K⁺ channels responsible for the delayed hyperpolarisation.     

Controlled gelation of xanthan by trivalent chronic ions

Addition of trivalent chromic ions to xanthan solutions gives rise to gel formation. The dynamic shear storage and loss moduli (0.01 – 10 rad/s) of xanthan solutions with polymer concentrations ranging from 1 to 7 mg/ml and Cr³⁺ concentrations ranging from 0 to 50 m have been studied. It is found that the rate of gel formation is strongly dependent on the Cr³⁺ concentration, but to a much smaller extent on the xanthan concentration. The gelation time is less than 1 h for 50 m Cr³⁺ and about 40 h for 2 m Cr³⁺. It is found that the minimum Cr³⁺ concentration needed to give gelation of 1–7 mg/ml xanthan is 1–2 m .     

Mode of action of recombinant Azotobacter vinelandii mannuronan C-5 epimerases AlgE2 and AlgE4.

The enzymes mannuronan C-5 epimerases catalyze conversion of beta-D-mannuronic acid to alpha-L-guluronic acid in alginates at the polymer level and thereby introduce sequences that have functional properties relevant to gelation. The enzymatic conversion by recombinant mannuronan C-5 epimerases AlgE4 and AlgE2 on alginate type substrates with different degree of polymerization and initial low fraction of alpha-L-guluronic acid was investigated. Essentially no enzymatic activity was found for fractionated mannuronan oligomer substrates with an average degree of polymerization, DP(n), less than or equal 6, whereas increasing the DP(n) yielded increased epimerization activity. This indicates that these enzymes have an active site consisting of binding domains for consecutive residues that requires interaction with 7 or more consecutive residues to show enzymatic activity. The experimentally determined kinetics of the reaction, and the residue sequence arrangement introduced by the epimerization, were modeled using Monte Carlo simulation accounting for the various competing intrachain substrates and assuming either a processive mode of action or preferred attack. The comparison between experimental data and simulation results suggests that epimerization by AlgE4 is best described by a processive mode of action, whereas the mode of action of AlgE2 appears to be more difficult to determine.     

On the role of extracellular Ca2+ for prolactin release and adenosine 3′:5′-monophosphate formation induced by thyroliberin in cultured rat pituitary cells

In cultured rat pituitary tumour cells (GH₃ cells) the absence of extracellular Ca⁺⁺ or addition of NaEGTA reduced spontaneous prolactin (PRL) release and abolished the stimulatory effect of thyroliberin (TRH). Readdition of CaCl₂, but not of equimolar concentrations of MgCl₂ increased spontaneous hormone release, and restored the effect of TRH. The calcium ionophore, A-23187, induced PRL release during normal calcium conditions, but not when an excess NaEGTA was present. TRH increased cyclic AMP accumulation in the presence and the absence of extracellular calcium. The effect of TRH on PRL release and cyclic AMP formation occured concomitantly with an increased efflux of ⁴⁵Ca²⁺. Intracellular electrophysiological recordings from the same single cells before and after TRH activation showed increased frequency and duration of the Ca²⁺ dependent action potentials. We conclude that TRH elevates the Ca²⁺ influx which depends on the depolarizing action current, and this effect is probably linked to formation of cyclic AMP and PRL release.     

Epidermal cell kinetics in the nude mouse

The epidermal cell kinetics in nude mice is investigated by determining the mitotic rate and the mitotic count, the H3Tdr labelling index, and the proportion of basal cells in the different cell cycle phases by flow cytometry. The mitotic duration was calculated. The parameter values of the epidermal cell kinetics of the nude mouse are largely similar to those of the hairless mouse.     

Older adults have unstable gait kinematics during weight transfer

The present article investigates gait stability of healthy older persons during weight transfer. Ten healthy older persons and ten younger persons walked 10 min each on a treadmill at 3 different gait speeds. The intra-stride change in gait stability was defined by the local divergence exponent λ(t) estimated by a newly developed method. The intra-stride changes in λ(t) during weight transfer were identified by separating each stride into a single and double support phase. The intra-stride changes in λ(t) were also compared to changes in the variation of the gait kinematics, i.e., SD(t). The healthy older persons walked at the same preferred walking speed as the younger persons. However, they exhibited significantly larger λ(t) (p<0.001) during weight transfer in the double support phase. Local divergence was closely related to intra-stride changes in SD(t) of the feet in the anterior-posterior direction. Furthermore, a high correlation was found between local divergence and the variation in step length and step width for both older (R>0.67, p<0.05) and younger persons (R>0.67, p<0.05). The present results indicate that the gait kinematics of older adults are more dynamical unstable during the weight transfer compared to younger persons. Furthermore, a close relationship exists between intra-stride changes in dynamical stability and variation in step length and step width. Further work will validate the results of the present study using real-life perturbations of the gait kinematics of both younger and older adults.     

Characterization In Vitro and In Vivo of Pandemic (H1N1) 2009 Influenza Viruses Isolated from Patients

The first influenza pandemic of the 21st century was caused by novel H1N1 viruses that emerged in early 2009. Molecular evolutionary analyses of the 2009 pandemic influenza A H1N1 [A(H1N1)pdm09] virus revealed two major clusters, cluster I and cluster II. Although the pathogenicity of viruses belonging to cluster I, which became extinct by the end of 2009, has been examined in a nonhuman primate model, the pathogenic potential of viruses belonging to cluster II, which has spread more widely in the world, has not been studied in this animal model. Here, we characterized two Norwegian isolates belonging to cluster II, namely, A/Norway/3568/2009 (Norway3568) and A/Norway/3487-2/2009 (Norway3487), which caused distinct clinical symptoms, despite their genetic similarity. We observed more efficient replication in cultured cells and delayed virus clearance from ferret respiratory organs for Norway3487 virus, which was isolated from a severe case, compared with the efficiency of replication and time of clearance of Norway3568 virus, which was isolated from a mild case. Moreover, Norway3487 virus to some extent caused more severe lung damage in nonhuman primates than did Norway3568 virus. Our data suggest that the distinct replicative and pathogenic potentials of these two viruses may result from differences in their biological properties (e.g., the receptor-binding specificity of hemagglutinin and viral polymerase activity).     

Chronic acetyl-L-carnitine alters brain energy metabolism and increases noradrenaline and serotonin content in healthy mice

Acetyl-L-carnitine (ALCAR), the short-chain ester of carnitine, is a common dietary supplement readily available in health food stores, claimed to improve energy levels and muscle strength. ALCAR has numerous effects on brain and muscle metabolism, protects against neurotoxic insults and may be an effective treatment for certain forms of depression. However, little is known about the effect of chronic ALCAR supplementation on the brain metabolism of healthy mice. Here, we investigated ALCAR's effect on cerebral energy and neurotransmitter metabolism after supplementing the drinking water of mice with ALCAR for 25 days, providing a daily dose of about 0.5 g/kg. Thereafter the animals were injected with [1-(13)C]glucose, and (13)C incorporation into and levels of various metabolites were quantified in extracts of the hippocampal formation (HF) and cortex using (1)H- and (13)C-nuclear magnetic resonance (NMR) spectroscopy and high performance liquid chromatography (HPLC). Increased glucose levels were detected in both regions together with a decreased amount of [3-(13)C]lactate, but no alterations in incorporation of (13)C derived from [1-(13)C]glucose into the amino acids glutamate, GABA and glutamine. These findings are consistent with decreased metabolism of glucose to lactate but not via the TCA cycle. Higher amounts of the sum of adenosine nucleotides, phosphocreatine and the phosphocreatine/creatine ratio found in the cortex of ALCAR-treated mice are indicative of increased energy levels. Furthermore, ALCAR supplementation increased the levels of the neurotransmitters noradrenaline in the HF and serotonin in cortex, consistent with ALCAR's potential efficacy for depressive symptoms. Other ALCAR-induced changes observed included reduced amounts of GABA in the HF and increased myo-inositol. In conclusion, chronic ALCAR supplementation decreased glucose metabolism to lactate, resulted in increased energy metabolite and altered monoamine neurotransmitter levels in the mouse brain.