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Biomedical subjects

N K Menon

Publications and source records attributed to N K Menon.

At least 19 recordsLinked to original sources
PubMed1992

Abnormal distribution of desmin and vimentin in myofibers in adult onset myotubular myopathy.

We report, for the first time, muscle immunocytochemical studies in sporadic, adult onset myotubular myopathy (SAOMM), which show intramyofibrillar central, perinuclear desmin and vimentin. This pattern was absent in a normal control and in myofibers with increased internal nuclei associated with denervation and myotonic muscular dystrophy (MyD). These findings resemble those reported in 8- to 15-week-old human fetal myotubes and myofibers of infantile MM, implying a possible regression of intermediate filaments of adult myofibers to an early developmental phase in SAOMM.

Desmin↗
PubMed1992

Calcium, calmodulin and 3',5'-cyclic nucleotide phosphodiesterase activity in human muscular disorders.

3',5'-Cyclic nucleotide phosphodiesterase (PDE) is known to play an important role in the regulation of cyclic nucleotide levels in various tissues including the muscle. Previous studies have estimated the level of this enzyme in several neuromuscular disorders but the results have been variable. Moreover, there was no attempt made to correlate the enzyme levels with the levels of calcium and calmodulin, both of which regulate diverse biological processes including muscle contraction. In the present study we have estimated phosphodiesterase in the muscle of normal controls as well as patients with myotonic (MyD) and Duchenne muscular dystrophy (DMD) and amyotrophic lateral sclerosis (ALS). PDE was found to be increased significantly in all of the diseased muscles as compared to controls (P less than 0.01). But the increase could be coupled with an increase in calcium and calmodulin only in Duchenne dystrophic muscle.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Reduction of biological effluents in purge and trap micro reaction vessels and detection of endothelium-derived nitric oxide (edno) by chemiluminescence.

Various analytical approaches have been used to measure endothelium-derived nitric oxide (NO). We have detected NO in perfusates with a sample size as low as 2 ml after acidification with 4 N HC1 to pH less than 2 at 25 degrees C by using a Nitric Oxide Analyser (Sievers, Colorado). This procedure had the advantage that the detectable level of NO was enhanced by the self-decomposition of HNO2 when the PH less than pKa of NHO2 (pKa = 3.15) and also the reaction temperature of 25 degrees C substantially increased the half-line of NO. Palmer, et al., measured NO released by cultured porcine endothelial cells by chemiluminescence after passing cell effluents continuously at a rate of 5 ml/min into 75 ml of 1% sodium iodide in glacial acetic acid. The larger volumes involved in this method for continuous refluxing, made it less desirable for the detection of endothelium-derived nitric oxide. Feelisch et al. utilized the activation of soluble guanylate cyclase, as well as, the quantitative oxidation of oxyhemoglobin to methemoglobin in aqueous solutions by NO as a means of measuring nitric oxide. We describe here a modification of our earlier micromethod which now enables us to detect NO after complete reduction with glacial acetic acid and sodium iodide. A comparison of the two procedures indicate that while freshly prepared NO standard solutions gave identical chemiluminescence response with and without reduction, effluents from bovine intrapulmonary artery under basal conditions gave substantially higher values upon reduction.

Animals↗
PubMed1991

Mutational analysis and characterization of the Escherichia coli hya operon, which encodes [NiFe] hydrogenase 1.

Deletion mutants of Escherichia coli specific for hydrogenase isoenzyme 1 (HYD1) have been constructed and characterized. The hya operon, which contains genes for the two HYD1 structural subunits and four additional genes, was mapped at 22 min on the E. coli chromosome. The total hydrogenase activities of the HYD1-negative mutant and wild-type strains were similar. However, the formate dehydrogenase activity associated with the formate hydrogen lyase pathway was lower in the mutant. The hya mutant (strain AP1), complemented with only the hydrogenase structural genes (hyaAB), produced antigenically identifiable but inactive HYD1 protein. The first five genes of hya (hyaA to hyaE) were required for the synthesis of active HYD1, but wild-type levels of HYD1 activity were restored only when mutant cells were transformed with all six genes of the operon. When AP1 was complemented with hya carried on a high-copy-number plasmid, the HYD1 structural subunits were overexpressed, but the excess protein was unprocessed and localized in the soluble fraction of the cell. The products of hyaDEF are postulated to be involved in the processing of nascent structural subunits (HYAA and HYAB). This processing takes place only after the subunits are inserted into the cell membrane. It is concluded that the biosynthesis of active HYD1 is a complex biochemical process involving the cellular localization and processing of nascent structural subunits, which are in turn dependent on the insertion of nickel into the nascent HYD1 large subunit.

Chromosome Deletion↗
PubMed1991

Nitroarginine does not inhibit lysophosphatidylcholine (LPC)-induced vascular relaxation and accumulation of cyclic GMP.

Lysophosphatidylcholine (LPC) is a potent endothelium-dependent vascular smooth muscle relaxant. The possibility that its action is mediated through endothelium-derived nitric oxide (EDNO), although suggestive, has not been proven. Both lysophosphatidylcholine and endothelium-derived nitric oxide relax by activating guanylate cyclase to form cyclic GMP. Based on the finding that EDNO formation is inhibited by NNA (N-omega-nitro-L-arginine), we followed cyclic GMP changes in bovine intrapulmonary arteries with LPC after incubation with NNA. Inhibition of cyclic GMP by LPC following NNA exposure would be suggestive of the production of EDNO by LPC. However, while NNA significantly inhibited accumulation of cyclic GMP after exposure to the calcium ionophore A23187 which releases EDNO, NNA failed to inhibit LPC-induced accumulation of cyclic GMP. The results indicate that LPC relaxes vascular smooth muscle through a non NO-mediated pathway.

Animals↗
PubMed1990

Localization of membrane-associated (NiFe) and (NiFeSe) hydrogenases of Desulfovibrio vulgaris using immunoelectron microscopic procedures.

The intracellular location of membrane-associated (NiFe) and (NiFeSe) hydrogenases of Desulfovibrio vulgaris was determined using pre-embedding and post-embedding immunoelectron microscopic procedures. Polyclonal antisera directed against the purified (NiFe) and (NiFeSe) hydrogenases were raised in rabbits. One-day-old cultures of D. vulgaris, grown on a lactate/sulfate medium, were used for all experiments in these studies. For post-embedding labeling studies cells were fixed with 0.2% glutaraldehyde and 0.3% formaldehyde, dehydrated with methanol, and embedded in the low-temperature resin Lowicryl K4M. Our post-embedding studies using antibody-gold or protein-A-gold as electron-dense markers revealed the location of the two hydrogenases exclusively at the cell periphery; the precise membrane location was then demonstrated by pre-embedding labeling. Spheroplasts were incubated with the polyclonal antisera against (NiFe) and (NiFeSe) hydrogenase followed by ferritin-linked secondary antibodies prior to embedding and sectioning. The observed labeling pattern unequivocally revealed that the antigenic reactive sites of the (NiFe) hydrogenase are located in the near vicinity of the cytoplasmic membrane facing into the periplasmic space, whereas the (NiFeSe) hydrogenase is associated with the cytoplasmic side of the cytoplasmic membrane.

Binding Sites↗
PubMed1990

An analysis of the regions of the myelin basic protein that bind to phosphatidylcholine.

The interactions of phosphatidylcholine (PC) to regions of the myelin basic protein (MBP) was examined. In solid phase binding assays the nature of the binding of unilamellar vesicles of 14C-labeled phosphatidylcholine to bovine 18.5 kDa MBP, its N- and C-terminal peptide fragments, photooxidized 18.5 kDa MBP and the mouse 14 kDa protein, with an internal deletion of residues 117-157, was studied. The data were analyzed by computer-generated Scatchard plots in which non-specific binding was eliminated. Non-cooperative, low affinity binding of PC vesicles to MBP was observed, and this binding found to be sensitive to pH and ionic changes. At an ionic strength of 0.1 and pH 7.4, the binding of PC to the 14 kDa mouse MBP exhibited a Kd similar to that obtained with both the N-terminal and photooxidized 18.5 kDa bovine MBP. The studies indicated that the sites of PC interaction with MBP are located in the N-terminal region of the protein. The C-terminal region appeared to modulate the strength of the interaction slightly. Under similar conditions, lysozyme did not bind PC liposomes, and histone bound them nonspecifically.

Animals↗
PubMed1990

A model to study physiological activation of phospholipase A2 and vasorelaxation by lysophosphatidylcholine.

Earlier we demonstrated that micellar solutions of LPC caused endothelium-dependent relaxation of rabbit thoracic aorta and bovine intrapulmonary artery and vein through a cyclic GMP-dependent mechanism. The availability of LPC for vasorelaxation depends on its production by deacylation of PC by PLA2. We assessed the possible activation of PLA2 by commonly used vasorelaxants such as acetylcholine, bradykinin, calcium ionophore A23187 and thrombin and vasoconstrictors like histamine and phenylephrine in the presence of indomethacin in a model system where 14C PC was incorporated into bovine intrapulmonary arterial segments. Taking the ratio of 14C PC:LPC formed by exogenous PLA2 as an index of deacylation, we found that while all the agents relaxed the strips in an endothelium-dependent manner, only thrombin caused relaxation followed by an increase in 14C LPC and a concomittant decrease in 14C PC indicating activation of PLA2. Our data show that PC/PLA2 system can be activated to generate LPC for vascular relaxation under specific physiological conditions. This model system can be used to monitor PLA2 activity and LPC production to compensate flow and pressure induced changes in arteries.

Acetylcholine↗
PubMed1990

Cloning and sequencing of a putative Escherichia coli [NiFe] hydrogenase-1 operon containing six open reading frames.

DNA encompassing the structural genes of an Escherichia coli [NiFe] hydrogenase has been cloned and sequenced. The genes were identified as those encoding the large and small subunits of hydrogenase isozyme 1 based on NH2-terminal sequences of purified subunits (kindly provided by K. Francis and K. T. Shanmugam). The structural genes formed part of a putative operon that contained four additional open reading frames. We have designated the operon hya and the six open reading frames hyaA through F. hyaA and hyaB encode the small and large structural subunits, respectively. The nucleotide-derived amino acid sequence of hyaC has a calculated molecular mass of 27.6 kilodaltons, contains 20% aromatic residues, and has four potential membrane-spanning regions. Open reading frames hyaD through F could encode polypeptides of 21.5, 14.9, and 31.5 kilodaltons, respectively. These putative peptides have no homology to other reported protein sequences, and their functions are unknown.

Amino Acid Sequence↗
PubMed1989

Effect of lysophosphatidylcholine on atherosclerotic rabbit arteries.

We report here on the effect of an endothelium-dependent vascular smooth muscle relaxant, lysophosphatidylcholine (LPC) on rabbit aortic strips and on hemodynamic changes by LPC in atherosclerotic animals. Cyclic GMP changes induced by LPC in atherosclerotic vessels were also determined. Atherosclerosis was produced by feeding a high cholesterol and saturated fatty acid diet. LPC was injected into the left atrium and coronary flow was measured by radioactive microspheres; in vitro, relaxation of precontracted aortic strips by lysophosphatidylcholine was also recorded. LPC failed to increase coronary flow in the presence of atherosclerosis. In isolated aortic strips, dose-response curves with acetylcholine and LPC showed diminished relaxation in atherosclerotic preparations, and cyclic GMP production following LPC was reduced. The results demonstrate that vascular relaxation by LPC, together with its ability to activate guanylate cyclase is dependent on the functional and morphological integrity of the vascular wall.

Animals↗
PubMed1989

Correlation of lysophosphatidylcholine-induced vs spontaneous relaxation to cyclic GMP levels in rabbit thoracic aorta.

We demonstrated previously that 10(-5)M micellar solution of lysophosphatidylcholine (LPC) produced relaxation of rabbit thoracic aorta in a dose-dependent manner. It was also noticed that histamine (HA)-precontracted strips relaxed spontaneously in the absence of LPC. We now measured the cyclic GMP changes during these two types of relaxation. Results indicate that while LPC-induced relaxation was mediated through cyclic GMP, spontaneous relaxation was not. The vasodilating effect of LPC was not due to its interference with cellular viability by solubilizing the membrane, because repeated additions of LPC produced identical degrees of relaxation and after three consecutive additions of LPC, the strips continued to relax to the same degree with acetylcholine (Ach) demonstrating the functional integrity of the endothelium. LPC/Cholesterol dispersions (1:0.5 mole percent) relaxed the strips to the same extent as the micellar solution of LPC, while 1:1 mole percent did not. The results stress the role of cyclic GMP in LPC-induced relaxation. They further suggest that LPC/Cholesterol ratio may determine the availability of LPC and regulate LPC-mediated processes.

Animals↗
PubMed1989

Severe hypokalemic rhabdomyolysis due to ingestion of liquorice during Ramadan.

A 62-year-old man was admitted with severe hypokalemia following ingestion of a modest amount of liquorice during the Islamic holy month of Ramadan. Hypokalemia was associated with typical electrocardiographic changes, marked acid-base disturbance and complicated by rhabdomyolysis. All abnormalities improved with normalisation of serum potassium. The serum creatine kinase isoenzymes (CK-total and MB) returned to normal over a prolonged period. The potential danger of ingesting liquorice even in small amounts over short periods, and the role of concomitant diuretic therapy with the additional factor of fasting during Ramadan in precipitating hypokalemia during liquorice ingestion are discussed.

Carbonated Beverages↗
PubMed1989

Analysis and comparison of nucleotide sequences encoding the genes for [NiFe] and [NiFeSe] hydrogenases from Desulfovibrio gigas and Desulfovibrio baculatus.

The nucleotide sequences encoding the [NiFe] hydrogenase from Desulfovibrio gigas and the [NiFeSe] hydrogenase from Desulfovibrio baculatus (N.K. Menon, H.D. Peck, Jr., J. LeGall, and A.E. Przybyla, J. Bacteriol. 169:5401-5407, 1987; C. Li, H.D. Peck, Jr., J. LeGall, and A.E. Przybyla, DNA 6:539-551, 1987) were analyzed by the codon usage method of Staden and McLachlan. The reported reading frames were found to contain regions of low codon probability which are matched by more probable sequences in other frames. Renewed nucleotide sequencing showed the probable frames to be correct. The corrected sequences of the two small and large subunits share a significant degree of sequence homology. The small subunit, which contains 10 conserved cysteine residues, is likely to coordinate at least 2 iron-sulfur clusters, while the finding of a selenocysteine codon (TGA) near the 3' end of the [NiFeSe] large-subunit gene matched by a regular cysteine codon (TGC) in the [NiFe] large-subunit gene indicates the presence of some of the ligands to the active-site nickel in the large subunit.

Amino Acid Sequence↗
PubMed1989

An improved chemiluminescence assay suggests non nitric oxide-mediated action of lysophosphatidylcholine and acetylcholine.

Using a new nitric oxide analyser, we have developed a sensitive chemiluminescence assay to detect trace quantities of NO in aqueous solutions. This improved technique in combination with the bioassay has been employed to verify the theory that NO released by vascular endothelium, accounts for the relaxation produced by acetylcholine, lysophosphatidylcholine and calcium ionophore A23187. Our results show that while calcium ionophore A23187 continuously released NO, acetylcholine and lysophosphatidylcholine relaxed vascular strips without releasing NO over the basal level.

Acetylcholine↗
PubMed1988

Lysolecithins as endothelium-dependent vascular smooth muscle relaxants that differ from endothelium-derived relaxing factor (nitric oxide)

The effects of lysolecithin (lysophosphatidylcholine) derived from egg yolk as well as of synthetic lysolecithins with different aliphatic chain lengths on tension development of rabbit aortic strips were investigated. Lysolecithins caused slowly progressing, dose-dependent relaxation that was inhibited by hemoglobin, methylene blue, and nordihydroguiaretic acid. Indomethacin caused no inhibition of relaxation. The degree of relaxation was endothelium-dependent and appeared to be related to the activation of guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2]. Superoxide dismutase failed to influence relaxation. Lysolecithins with the longest aliphatic chain were the most potent relaxants of aortic strips. The experiments suggest a role of lysolecithins through their weak detergent action on membrane dynamics of endothelial cells, resulting in the production of cyclic GMP and the relaxation of arterial smooth muscle. Lysolecithins differ in several respects from endothelium-derived relaxing factor. Endothelium-derived relaxing factor is an unstable humoral substance released from endothelium and is identical to nitric oxide, itself a labile substance causing vascular relaxation and cyclic GMP accumulation. Lysolecithins may represent a different type of endothelium-dependent muscle relaxant.

Acetylcholine↗