Remote reperfusion lung injury is associated with AMP deaminase 3 activation and attenuated by inosine monophosphate.

BACKGROUND: Remote reperfusion lung injury occurs in patients with vascular occlusion and surgical procedures. Inosine monophosphate (IMP) produced by adenosine monophosphate deaminase (AMPD) 3 is involved in the remote reperfusion injury. The purpose of the present study was to identify whether IMP administration attenuated the remote reperfusion lung injury in a skeletal muscle ischemia-reperfusion model. METHODS AND RESULTS: A remote reperfusion lung injury was created using reperfusion after the bilateral ligation of the hind-limb. AMPD activity, myeloperoxidase (MPO) activity, IMP, AMPD3 mRNA and tumor necrosis factor (TNF)-alpha in the lungs before and after reperfusion were analyzed. Furthermore, the effects of IMP on these parameters were examined. AMPD3 mRNA, AMPD activity and IMP production in the lungs significantly increased after ischemia-reperfusion with increases in MPO activity, TNF-alpha level and decreased oxygen saturation (SpO(2)). Histological examination of the lungs demonstrated significant neutrophil infiltration and accumulation. IMP administration significantly reduced MPO activity, TNF-alpha and neutrophil infiltration, with ameliorated SpO(2). CONCLUSIONS: Along with the activation of AMPD3, ischemia-reperfusion-induced lung inflammation is associated with increased MPO activity and TNF-alpha level. IMP significantly decreased the lung injury, MPO activity, TNF-alpha and increased SpO(2). These findings may lead to the development of a new therapeutic strategy for remote reperfusion lung injury.

Introductory remarks on umami taste.

Psychophysical and electrophysiological studies indicated that the umami substances have no enhancing activity on other primary tastes. Experiments using amiloride clearly show that the umami component of canine chorda tympani nerve response to umami substances is independent of the salt component. Single fiber analysis of the responses of the mouse glossopharyngeal nerve and the monkey primary taste cortex neuron show that the responses to umami substances are independent of other primary tastes. A large synergism between monosodium glutamate (MSG) and disodium 5'-inosinate (IMP) or disodium 5'-guanylate (GMP) is observed in dogs and is explained in terms of allosteric effect. The order of intensity of umami taste induced by a mixture of 0.5 mM GMP and 1.5 mM of various agonists for the glutamate receptors was glutamate > ibotenate > DL(+)-2-amino-4-phosphonobutyric acid (DL-AP4)-(+)-1- aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD). Kainate, N-methyl-D-aspartate (NMDA) and (RS)--amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), which are agonists for ionotropic receptors, have no umami taste. It was concluded that the umami receptor is not identical to any of known glutamate receptors, and there seems to be a unique receptor for umami.

Response of compressed skinned skeletal muscle fibers to conditions that simulate fatigue.

During fatigue, muscles become weaker, slower, and more economical at producing tension. Studies of skinned muscle fibers can explain some but not all of these effects, and, in particular, they are less economical in conditions that simulate fatigue. We investigated three factors that may contribute to the different behavior of skinned fibers. 1) Skinned fibers have increased myofilament lattice spacing, which is reversible by osmotic compression. 2) A myosin subunit becomes phosphorylated during fatigue. 3) Inosine 5'-monophosphate (IMP) accumulates during fatigue. We tested the response of phosphorylated and unphosphorylated single skinned fibers (isometric tension, contraction velocity, and adenosinetriphosphatase activity) to changes in lattice spacing (0-5% dextran) and IMP (0-5 mM) in the presence of altered concentrations of P(i) (3-25 mM), H+ (pH 7-6.2), and ADP (0-5 mM). The response of maximally activated skinned fibers to the direct metabolites of ATP hydrolysis is not altered by osmotic compression, phosphorylating myosin subunits, or increasing IMP concentration. These factors, therefore, do not explain the discrepancy between intact and skinned fibers during fatigue.

AMP degradation in the perfused rat heart during 2-deoxy-D-glucose perfusion and anoxia. Part II: The determination of the degradation pathways using an adenosine deaminase inhibitor.

Using the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), we determine the contribution of the adenosine pathway to the abundant purine release of two Langendroff-perfused rat heart models which differ particularly in inorganic phosphate (Pi) content: the 2-deoxy-D-glucose (2DG) perfused heart and the anoxic heart. We measure the release of coronary purines by high performance liquid chromatography, and the content of myocardial metabolites by 31P nuclear magnetic resonance spectroscopy. In the 2DG-perfused heart (2 mM for 45 min), the release of inosine [130 nmol/(min.gww)] is much larger than that of adenosine, and EHNA (50 microM) has little effect, showing that the pathway of inosine monophosphate (IMP) accounts for 97% of purine catabolism. In the anoxic heart (100% N2 for 45 min), where inosine and adenosine release are comparable in the absence of EHNA, the inhibitor reduces the release of inosine and catabolites from 50 to 20 nmol/(min.gww) and increases that of adenosine [from 30 to 55 nmol/(min.gww)], showing that the contributions of the IMP and adenosine pathways are 23 and 77%. The difference between the two models has been ascribed to the inhibition of AMP deaminase by Pi in the anoxic heart (Chen W, et al., 1996). We discuss the physiological significance of this heart-specific duality of degradation pathways.

Neuronal responses of the nucleus tractus solitarius to oral stimulation with umami substances.

In order to investigate coding mechanisms of special taste modality (umami), responses of neurons within the nucleus tractus solitarius (NTS) to oral stimulation with monosodium glutamate, disodium 5'-inosinate (IMP) or their mixture were recorded in the conventional electrophysiological method. Results obtained were as follows: Neither MSG-best nor IMP-best neuron was recorded within the NTS as in the primary taste afferents. Some of the sucrose-best neurons, NaCl-best neurons and HCl-best neurons responded to oral stimulation with MSG or IMP. A remarkable synergistic effect was observed in all of the sucrose-best neurons and in some of the NaCl-best neurons but not in all of the HCl-best neurons, when the mixed solution of MSG and IMP was applied into the oral cavity. As to the sucrose-best neurons, potency of the synergism was positively correlated with the responsiveness to sucrose. No correlation was recognized between them in the case of NaCl-best neurons. These results suggest a view that the sucrose-best neurons and the NaCl-best neurons which show the synergism may participate in coding umami taste.

Taste of glutamate salts in young and elderly subjects: role of inosine 5'-monophosphate and ions.

Taste sensitivity to five glutamate salts (sodium glutamate, potassium glutamate, ammonium glutamate, calcium diglutamate, and magnesium diglutamate) were determined in sixteen young (mean age 25.58 years) and eighteen elderly (mean age 86.89 years) subjects. The effect of inosine 5'-monophosphate (IMP) and ions on taste perception of glutamate compounds was also investigated. The detection thresholds for glutamate salts were 5.04 times higher in elderly subjects than in young subjects; the recognition thresholds were 3.84 times higher. For young subjects, 0.1 mM IMP lowered detection and recognition thresholds for all 5 salts. A stronger concentration of IMP (1 mM) had this effect in both young and elderly groups. Elderly subjects perceived suprathreshold concentrations as less intense than young subjects. Chloride and acetate salts of sodium, potassium, and calcium reduced the detection and recognition thresholds of L-glutamic acid but had no effect sodium glutamate thresholds.

Glycogenolysis during recovery from muscular work. The time course of phosphorylase activity is dependent on Pi concentration in the abdominal muscle of the shrimp Crangon crangon.

1) Glycogen is degraded in the abdominal muscle of the shrimp Crangon crangon (Decapoda, Crustacea) during the recovery period following work. The regulation of post-exercise glycogen breakdown and the properties of glycogen phosphorylase (EC 2.4.1.1) have been studied: 2) Glycogen phosphorylase exists as unphosphorylated b-form and phosphorylated a-form, the latter contains 1 molecule phosphate/subunit. Both forms of phosphorylase are dimers, isoenzymes have not been detected. 3) The purified b-form is inactive in absence of AMP and has very low affinities for AMP and Pi. For half-maximum activation 0.33 +/- 0.04 mM AMP is necessary, and the Km-value for Pi at 1 mM AMP is 48 +/- 5 mM. IMP does not affect the activity of the b-form. 4) The a-form is active without effectors, its Km-value for Pi is 5.3 +/- 1.5 mM. The proportion of phosphorylase a increases in vivo, from about 25% at rest, to approximately 90% upon work and remains at this high level during the first minutes of recovery. 5) It is concluded that the glycogenolytic flux in the abdominal muscle of the shrimp even during post-exercise periods depends on the level of the a-form the activity of which is restricted in time and extent by the cytoplasmic Pi concentration (Kamp, G. & Juretschke, H. P. (1987) Biochim. Biophys. Acta 929, 121-127).

Taste effects of 'umami' substances in hamsters as studied by electrophysiological and conditioned taste aversion techniques.

Behavioral and electrophysiological experiments were performed to examine whether or not the taste of 'umami' substances such as monosodium glutamate (MSG), disodium 5'-inosinate (IMP), and disodium 5'-guanilate (GMP) is really unique in hamsters. When the animals were conditioned to avoid ingestion of MSG (or IMP) or their mixture by pairing its ingestion with an i.p. injection of LiCl, suppression of drinking generalized to IMP (or MSG), GMP, NaCl, and other sodium salts. Suppression of drinking after conditioning to NaCl generalized to MSG, IMP, GMP, and inorganic sodium salts. These learned aversions to umami substances and sodium salts were abolished by bilateral deafferentation of the chorda tympani, but were not affected by destruction of the bilateral glossopharyngeal nerves. The integrated whole-nerve responses of the chorda tympani to MSG, IMP, and NaCl were similar to each other, consisting of the initial dynamic phase and the following tonic phase. Synergism of chorda tympani responses to a mixture of MSG and IMP was not observed. Across-fiber response patterns of the chorda tympani for MSG, IMP, or their mixture were very similar to that for NaCl. Even the high concentrations of umami substances (0.3 M MSG, 0.3 M IMP, and the mixture) did not elicit any detectable responses in the glossopharyngeal nerve. These results suggest that the taste of umami substances is not unique in the hamster, but is similar to that of sodium salts, and is mediated exclusively via the chorda tympani.

Role of inosine 5'-phosphate in activating glucose-bisphosphatase.

Glucose-bisphosphate (G1c-1,6-P2) phosphatase has been purified greater than 200-fold from the cytosol of mouse brain. As reported earlier, the enzyme requires inosine monophosphate (IMP) and Mg2+ for activity [Guha, S.K., & Rose, Z. B. (1982) J. Biol. Chem. 257, 6634-6637]. Kinetic parameters and the role of IMP have been further investigated. When Glc-1,6-P2 and IMP are both varied, double-reciprocal plots of the data form a parallel line pattern. With 2 mM Mg2+, the Km obtained for G1c-1,6-P2 is 20 microM and the Ka for IMP is 9 microM. Co2+, Mn2+, and Ni2+ activate less effectively than Mg2+. The apparent Ka for Mg2+ decreases with increasing G1c-1,6-P2, and the observed Km of G1c-1,6-P2 decreases with increasing Mg2+. The extrapolated value of the Ka of Mg2+ at infinite substrate is 86 microM. Mg2+ does not affect the Ka of IMP. The phosphatase activity is optimal at pH 7. The phosphatase is not completely specific since mannose 1,6-bisphosphate is hydrolyzed and guanosine monophosphate activates. However, fructose 1,6-bisphosphate is no more than a poor inhibitor, and adenine nucleotides are neither activators nor inhibitors. The products of the reaction are glucose-1-P and glucose-6-P, in a ratio of 2:3, and Pi. Both glucose-P's are competitive inhibitors with respect to IMP [Ki(glucose-1-P) = 5 microM; Ki(glucose-6-P) = 18 microM]. Neither glucose-P competes with G1c-1,6-P2. The demonstration of an exchange reaction between G1c-1,6-P2 and glucose-6-P is evidence for the phosphorylation of the enzyme by the substrate. The exchange reaction requires Mg2+ and is inhibited by IMP. The observation of the exchange reaction and its elimination by IMP indicates that the low level of phosphoglucomutase activity that remains with the phosphatase throughout purification is an inherent property of the phosphatase. The requirement of glucose-bisphosphatase for the nucleotide IMP is consistent with possible roles for both G1c-1,6-P2 and IMP in the control of the ATP level in the brain.