Characteristics of brain Kv1 channels tailored to mimic native counterparts by tandem linkage of alpha subunits: implications for K+ channelopathies

Most neuronal Kv1 channels contain Kv1.1, Kv1.2 alpha, and Kvbeta2.1 subunits, yet the influences of their stoichiometries on properties of the (alpha)(4)(beta)(4) variants remain undefined. cDNAs were engineered to contain 0, 1, 2, or 4 copies of Kv1.1 with the requisite number of Kv1.2 and co-expressed in mammalian cells with Kvbeta2.1 to achieve "native-like" hetero-oligomers. The monomeric (Kv1.1 or 1.2), dimeric (Kv1.1-1.2 or 1.2-1.2), and tetrameric (Kv1.1-(1.2)(3)) constructs produced proteins of M(r) approximately 62,000, 120,000, and 240,000, which assembled into (alpha)(4)(beta)(4) complexes. Each alpha cRNA yielded a distinct K(+) current in oocytes, with voltage dependence of activation being shifted negatively as the Kv1.1 content in tetramers was increased. Channels containing 1, 2, or 4 copies of Kv1.1 were blocked by dendrotoxin k (DTX)(k) with similarly high potencies, whereas Kv(1.2)(4) proved nonsusceptible. Accordingly, Kv1.2/beta2.1 expressed in baby hamster kidney cells failed to bind DTX(k); in contrast, oligomers containing only one Kv1.1 subunit in a tetramer exhibited high affinity, with additional copies causing modest increases. Thus, one Kv1.1 subunit largely confers high affinity for DTX(k), whereas channel electrophysiological properties are tailored by the content of Kv1.1 relative to Kv1.2. This notable advance could explain the diversity of symptoms of human episodic ataxia I, which is often accompanied by myokymia, due to mutated Kv1.1 being assembled in different combinations with wild-type and Kv1.2.     

Differential steric effects in the axial ligation of pyridine and imidazole to α- and β-alkylcobinamides

One subclass of B₁₂-requiring enzymes is now known to bind their B₁₂ coenzymes “base-off,” with a histidine residue from the protein supplying an imidazole ligand to the cobalt center. Recent results from Sirovatka and Finke (J.M. Sirovatka and R.G. Finke, J.Am. Chem. Soc. 119, (1997) 3057) show that imidazole has an extraordinary trans effect on the mode of carbon–cobalt bond cleavage in coenzyme B₁₂ analogs, compared to pyridine or the natural 5,6-dimethylbenzimidazole ligand, and it was suggested that a differential steric effect could, in part, account for the uniqueness of the imidazole ligand. Such a differential steric effect for imidazole and pyridine is now demonstrated by studies of the thermodynamics of ligation of these ligands to the α and β diastereomers of two alkylcobinamides (RCbi⁺s, derivatives of cobalamins which lack the normal axial nucleotide) based on the known differences in steric crowding of the α (“lower”) and β (“upper”) axial ligand positions of cobalt corrinoids. Imidazole binds more tightly than pyridine to both diastereomers of NCCH₂Cbi⁺ and CF₃Cbi⁺, in all cases due to a more favorable entropy change, which is the result of lowered steric interference with corrin side chain thermal motions.     

Studies on the protective effect of dietary fish oil on uranyl-nitrate-induced nephrotoxicity and oxidative damage in rat kidney

Human and animal exposure demonstrates that uranium is nephrotoxic. However, attempts to reduce it were not found suitable for clinical use. Dietary fish oil (FO) enriched in ω-3 fatty acids reduces the severity of cardiovascular and renal diseases. Present study investigates the protective effect of FO on uranyl nitrate (UN)-induced renal damage. Rats prefed with experimental diets for 15 days, given single nephrotoxic dose of UN (0.5 mg/kg body weight) intraperitoneally. After 5 d of UN treatment, serum/urine parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM), oxidative stress and phosphate transport were analyzed in rat kidney. UN nephrotoxicity was characterized by increased serum creatinine and blood urea nitrogen. UN increased the activity of lactate dehydrogenase and NADP-malic enzyme whereas decreased malate, isocitrate and glucose-6-phophate dehydrogenases; glucose-6-phophatase, fructose-1, 6-bisphosphatase and BBM enzyme activities. UN caused oxidant/antioxidant imbalances as reflected by increased lipid peroxidation, activities of superoxide dismutase, glutathione peroxidase and decreased catalase activity. Feeding FO alone increased activities of enzymes of glucose metabolism, BBM, oxidative stress and Pi transport. UN-elicited alterations were prevented by FO feeding. However, corn oil had no such effects and was not similarly effective. In conclusion, FO appears to protect against UN-induced nephrotoxicity by improving energy metabolism and antioxidant defense mechanism.     

Differential protein expression profile in the liver of pikeperch (Sander lucioperca) larvae fed with increasing levels of phospholipids

A comparative proteomic approach was used to assess the protein expression profile in the liver of 34 days old pikeperch larvae fed from day 10 post hatching, with three isoproteic and isolipidic formulated diets varying by their phospholipid (PL) contents (% dry diet weight): 1.4% (PL1), 4.7% (PL5) and 9.5% (PL9). Using 2D-DIGE minimal labelling of liver extracts, we were able to show 56 protein spots with a differential intensity (p < 0.05) depending on the dietary PL content. Among these spots, 11 proteins were unambiguously identified using nanoLC-MS/MS tandem mass spectrometry. In the PL9 larvae, our results indicate that the glycolytic pathway could be down-regulated due to the under-expression of the fructose biphosphate aldolase B and the phosphoglucomutase 1. Meanwhile, propionyl coenzyme A carboxylase (a gluconeogenic enzyme) was under-expressed. In addition, another gluconeogenic and lipogenic enzyme, pyruvate carboxylase, was identified in 3 different spots as being under-expressed in fish fed with the intermediate PL level (PL5). A high PL content increased the expression of sarcosine dehydrogenase, an enzyme involved in methionine metabolism, along with vinculin, a structural protein. Moreover, several stress proteins (glutathione S-transferase M, glucose regulated protein 75 and peroxiredoxin-1) were modulated in response to the dietary PL level and fatty acid composition. In the larvae fed with the lowest dietary PL content (PL1), over-expression of both GSTM and GRP75 might indicate a cellular stress in this experimental treatment, while the under-expression of Prx1 might indicate a lower defence against oxidative stress. In conclusion, this nutriproteomic approach showed significant modifications of protein expression in the liver of pikeperch larvae fed different PL contents, highlighting the importance of these nutrients and their influence on metabolism processes and on stress response.     

SHER: A Colored Petri Net Based Random Mobility Model for Wireless Communications

In wireless network research, simulation is the most imperative technique to investigate the network’s behavior and validation. Wireless networks typically consist of mobile hosts; therefore, the degree of validation is influenced by the underlying mobility model, and synthetic models are implemented in simulators because real life traces are not widely available. In wireless communications, mobility is an integral part while the key role of a mobility model is to mimic the real life traveling patterns to study. The performance of routing protocols and mobility management strategies e.g. paging, registration and handoff is highly dependent to the selected mobility model. In this paper, we devise and evaluate the Show Home and Exclusive Regions (SHER), a novel two-dimensional (2-D) Colored Petri net (CPN) based formal random mobility model, which exhibits sociological behavior of a user. The model captures hotspots where a user frequently visits and spends time. Our solution eliminates six key issues of the random mobility models, i.e., sudden stops, memoryless movements, border effect, temporal dependency of velocity, pause time dependency, and speed decay in a single model. The proposed model is able to predict the future location of a mobile user and ultimately improves the performance of wireless communication networks. The model follows a uniform nodal distribution and is a mini simulator, which exhibits interesting mobility patterns. The model is also helpful to those who are not familiar with the formal modeling, and users can extract meaningful information with a single mouse-click. It is noteworthy that capturing dynamic mobility patterns through CPN is the most challenging and virulent activity of the presented research. Statistical and reachability analysis techniques are presented to elucidate and validate the performance of our proposed mobility model. The state space methods allow us to algorithmically derive the system behavior and rectify the errors of our proposed model.     

Molecular determinants of the binding specificity of BH3 ligands to BclXL apoptotic repressor

B‐cell lymphoma extra‐large protein (BclXL) serves as an apoptotic repressor by virtue of its ability to recognize and bind to BH3 domains found within a diverse array of proapoptotic regulators. Herein, we investigate the molecular basis of the specificity of the binding of proapoptotic BH3 ligands to BclXL. Our data reveal that while the BH3 ligands harboring the LXXX[A/S]D and [R/Q]XLXXXGD motif bind to BclXL with high affinity in the submicromolar range, those with the LXXXGD motif afford weak interactions. This suggests that the presence of a glycine at the fourth position (G+4)—relative to the N‐terminal leucine (L0) within the LXXXGD motif—mitigates binding, unless the LXXXGD motif also contains arginine/glutamine at the ?2 position. Of particular note is the observation that the residues at the +4 and ?2 positions within the LXXX[A/S]D and [R/Q]XLXXXGD motifs appear to be energetically coupled—replacement of either [A/S]+4 or [R/Q]‐2 with other residues has little bearing on the binding affinity of BH3 ligands harboring one of these motifs. Collectively, our study lends new molecular insights into understanding the binding specificity of BH3 ligands to BclXL with important consequences on the design of novel anticancer drugs. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 573–582, 2014.     

Anaesthetic considerations of adults with Morquio's syndrome - a case report

Background

Base deficit (BD) is commonly used in the operating room (OR) as an endpoint of resuscitation. BD is used as a surrogate marker for the accumulation of lactic acid(Lac). However, the BD can be affected by large amounts of saline.

Methods

We conducted a survey of anesthesiologists regarding the use of BD. We also studied the reliability of BD to determine the presence of hyperlactatemia (HL). Patients undergoing general anesthesia were eligible for enrollment if they were receiving an arterial line as part of their routine care. If an arterial blood gas was drawn by the operative team as part of the routine care, the remainder of the unused blood was also used to measure Lac.

Results

Survey: 73 staff anesthesiologists were surveyed. Over 70% of respondents used BD as an endpoint of resuscitation. Base Deficit Study: 35 patients were enrolled resulting in 88 arterial blood gases with corresponding Lac. Mean age was 61.4 ± 14.3 years, 43% were male. Mean pH was 7.39 ± 0.05, the mean bicarbonate was 23.0 ± 2.3 meq/L, the mean BD 1.34 ± 2.3, and the mean Lac was 1.58 ± 0.71 mmol/L. Mean ASA risk score was 3.16 ± 0.71. ROC area under the curve for base deficit to detect HL was 0.58.

Conclusion

BD can often mislead the clinician as to the actual Lac. Lac can now be measured in the OR in real time. Therefore, if clinicians in the operative setting want to know the Lac, it should be measured directly.