Intersegmental Coordination: Lessons from Modeling Systems of Coupled Non-Linear Oscillators

SYNOPSIS. Intersegmental coordination of both vertebrates andinvertebrates is poorly understood primarily because so littleis known about the substrate of the neural underpinnings andhow the elements interact to produce the complex timing relationshipsrequired by the organism. We describe here a systems approachcombining experimental and theoretical treatment of the lampreylocomotor central pattern generator. The central pattern generatoris viewed as a chain of coupled non-linear oscillators correspondingto segmental burst generators. We analyze various coupling schemesin terms of their ability to produce a stable traveling wavesimilar to that seen in the isolated spinal cord and the intactanimal. The role of long coordinating neurons is particularlydiscussed.     

Stereospecific high-performance liquid chromatographic assay of ibuprofen: improved sensitivity and sample processing efficiency

A high-performance liquid chromatographic (HPLC) assay suitable for the analysis of the enantiomers of the non-steroidal anti-inflammatory drug ibuprofen (IB) in plasma was developed. Following the addition of racemic fenoprofen as internal standard (I.S.), samples are acidified and extracted with a mixture of isooctane—isopropanol (95:5, v/v). After evaporation of the organic layer, the drug and I.S. are derivatized with S-(−)-1(1-naphthyl)ethylamine (S-NEA) after addition of ethyl chloroformate as the coupling reagent. Ethanolamine is added 3 min after the addition of S-NEA to react with the excessive ethyl chloroformate. The resultant diastereomers corresponding to IB and I.S. were chromatographed at ambient temperature on a 100 mm × 4.6 mm I.D. C₁₈ reversed-phase column using acetonitrile—water—acetic acid—triethylamine (60:40:0.1:0.02) as the mobile phase pumped at a flow-rate of 1.2 ml/min. Detection of the fluorescent chromophore was at 280 and 320 nm for excitation and emission, respectively. The suitability of the assay for clinical pharmacokinetic studies of IB was determined by the analysis of plasma samples obtained from a healthy volunteer, following administration of a single 400-mg oral dose of racemic IB.     

Properties of aspartate racemase, a pyridoxal 5'-phosphate-independent amino acid racemase.

Aspartate racemase from Streptococcus thermophilus contains no pyridoxal 5'-phosphate or other cofactors such as FAD, NAD+, and metal ions. It was affected by neither carbonyl reagents such as hydroxylamine nor sodium borohydride but was strongly inhibited by iodoacetamide and other thiol reagents. Aspartate, cysteate, and cysteine sulfinate were the only substrates. The Km values for L- and D-aspartate were 35 and 8.7 mM, respectively. The enzyme catalyzed the exchange of alpha-hydrogen of the substrate with the solvent hydrogen. Racemization of L-aspartate in 2H2O showed an overshooting in the optical rotation of aspartate before the substrate was fully racemized. This shows that the removal of alpha-hydrogen of the substrate is at least partially rate-determining. When L- or D-aspartate was incubated with aspartate racemase in tritiated water, tritium was incorporated preferentially into the product enantiomer. The results strongly suggest that aspartate racemase contains two hydrogen acceptors.     

A novel 145 kd brain cytosolic protein reconstitutes Ca(2+)-regulated secretion in permeable neuroendocrine cells.

The regulated secretory pathway is activated by elevated cytoplasmic Ca2+; however, the components mediating Ca2+ regulation have not been identified. In semi-intact neuroendocrine cells, Ca(2+)-activated secretion is ATP- and cytosol protein-dependent. We have identified a novel brain protein, p145, as a cytosolic factor that reconstitutes Ca(2+)-activated secretion in two neuroendocrine cell types. The protein is a dimer of 145 kd subunits, exhibits Ca(2+)-dependent interaction with a hydrophobic matrix, and binds phospholipid vesicles, suggesting a membrane-associated function. A p145-specific antibody inhibits the reconstitution of Ca(2+)-activated secretion by cytosol, indicating an essential role for p145. The restricted expression of p145 in tissues exhibiting a regulated secretory pathway suggests a key role for this protein in the transduction of Ca2+ signals into vectorial membrane fusion events.     

Kinetics of Nitrosomonas europaea at extreme substrate,product and salt concentrations

Summary Nitrification of ammonia in concentrated waste streams is gaining a lot of attention nowadays. Nitrosomonas europaea is the predominant ammonia-oxidizing species in these environments. Prediction of the behaviour of a pure culture of N. europaea (ATCC 19718) under conditions prevailing in concentrated waste streams was the aim of this study. The initial oxygen consumption rate of a concentrated cell suspension was used as a rapid assay to measure the effects on N. europaea under various conditions. Several relationships, based on Michaelis-Menten kinetics, were derived. They describe the behaviour of N. europaea at substrate (NH₄ ⁺), product (NO₂ ^– and K⁺, Na⁺, SO _inf4 ^sup2– , NO₃ ^–, Cl^–) concentrations up to 500 mol/m³ and pHs ranging from 6.5 to 8.5. High concentrations of ions inhibited N. europaea but specific substrate inhibition was not observed. Product inhibition was strongly pH-dependent and severe inhibition was found at pH 6.5. Correspondence to: J. H. Hunik     

Merkel cell tumor of the back detected during pregnancy

Merkel cell tumor is an unusual, aggressive malignancy of skin that has been considered to be derived from cutaneous Merkel cells. We are reporting a case of Merkel cell tumor overlying the left scapula with metastases to the thoracic spine and pleura. The tumor was found incidentally in a 23-year-old pregnant black woman. The tumor recurred locally 5 months after initial wide excision. Subsequently, a second wide excision of the recurrent tumor with ipsilateral axillary dissection was performed. The course of the disease was complicated by local recurrence and formation of distant metastases to pleura and spine. At the end-stage of the disease, the patient was found to have a cardiac murmur, and echocardiography revealed a mass in the anterior wall of the right ventricle that was suspicious for a metastatic lesion. The patient expired from extensive distant metastases 23 months after diagnosis.     

Formation of 20-oxoleukotriene B4 by an alcohol dehydrogenase isolated from human neutrophils

When 20-hydroxyleukotriene B4 (20-OH-LTB4) is incubated at pH 10.5 in the presence of NAD+ with an alcohol dehydrogenase isolated from human neutrophils, a polar product is formed as detected on reverse-phase high-performance liquid chromatography (RP-HPLC). The product is identified as 20-oxo-LTB4 (20-CHO-LTB4) on the basis of its co-elution with the authentic compound on HPLC, ultraviolet spectrometry and gas chromatography-mass spectrometry. The 20-CHO-LTB4-forming activity requires NAD+, but NADP+ scarcely replaces NAD+. The apparent Km for 20-OH-LTB4 is 83 microM and the Vmax is 2.04 mumol/min per mg of protein. The activity is inhibited by omega-hydroxy fatty acids such as 12-hydroxylauric acid, 16-hydroxypalmitic acid and 12(S), 20-dihydroxyeicosatetraenoic acid, but not by 4-methylpyrazole. At pH 7.0 with NADH, the purified dehydrogenase catalyzes the reverse reaction, the reduction of 20-CHO-LTB4 to 20-OH-LTB4.     

Effects of hypoxia and fatty acids on the distribution of metabolites in rat heart

The effects of exogenous fatty acids and hypoxia on cardiac energy metabolism were studied by measuring mitochondrial and cytosolic adenine nucleotides as well as CoA and carnitine esters using a tissue fractionation technique in non-aqueous solvents. During normoxia, the administration of 0.5 mM palmitate caused a considerable increase in acyl-CoA and acylcarnitine, particularly in mitochondria. High-energy phosphates, however, were only slightly altered. A 90 min low-flow hypoxia caused a dramatic increase in mitochondrial acyl esters. The mitochondrial ATP content decreased significantly, while the cytosolic concentration was only slightly diminished, suggesting an inhibition of mitochondrial adenine nucleotide translocation by long-chain acyl-CoA. Addition of palmitate during hypoxia amplified hypoxic damage and reduced adenine nucleotides in both compartments considerably, while fatty acid metabolites were only slightly affected. In presence of an inhibitor of fatty acid oxidation (BM 42.304), the fatty-acid-induced acceleration of cardiac injury was prevented. Since BM 42.304 decreased mitochondrial acylcarnitine and increased the cytosolic concentration significantly, BM 42.304 was presumed to inhibit mitochondrial acylcarnitine translocase. However, a causal relationship between lipid metabolites and ischemic damage seemed unlikely.