Effects of chemical ischemia on purine nucleotides, free radical generation, lipids peroxidation and intracellular calcium levels in C 2C12 myotube derived from mouse myocytes

To elucidate the mechanisms of ischemia-mediated myopathy using in vitro model, changes of purine nucleotides, membrane lipid peroxidation(TBARS), intracellular calcium ([Ca2+]i)levels, generation of free radicals, and deoxyribonucleic acid (DNA) fragmentation were examined in mouse-derived C2C12 myotubes under the condition with an inhibition of glycolytic and oxidative metabolism as the ischemic condition. In purine nucleotides, intracellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations rapidly and significantly decreased after the treatment with ischemia. No remarkable differences were observed in other purine nucleotides, with the exception of inosine monophosphate (IMP) and extracellular hypoxanthine levels, both of which increased significantly during the ischemia. The lactate dehydrogenase activity in culture supernatant of C2C12 myotubes increased significantly from 2 to 4 hr after the ischemia. On the generation of free radicals, no spectrum was detected in supernatants throughout the observation period, whereas supernatant TBARS concentration increased rapidly and significantly after the ischemia. The relative intensity of [Ca2+]i significantly increased after the ischemia. On the fragmented deoxyribonucleic acid(DNA), no TUNEL positive cells was detected in C2C12 myotubes after 1 hr of the ischemia, however the positive cell percentage subsequently increased. From these results, it was suggested that the ischemic condition induced changes of membrane permeability and increase of [Ca2+]i, both of which lead to cell membrane damage, although a free radical generation was not detected. The ischemic condition also induced the release of substrate hypoxanthine for free radical generation and might initiate the apoptotic pathway in C2C12 myotubes.Facultad de Ciencias Veterinaria

Effects of chemical ischemia on purine nucleotides, free radical generation, lipids peroxidation and intracellular calcium levels in C 2C12 myotube derived from mouse myocytes

To elucidate the mechanisms of ischemia-mediated myopathy using in vitro model, changes of purine nucleotides, membrane lipid peroxidation(TBARS), intracellular calcium ([Ca2+]i)levels, generation of free radicals, and deoxyribonucleic acid (DNA) fragmentation were examined in mouse-derived C2C12 myotubes under the condition with an inhibition of glycolytic and oxidative metabolism as the ischemic condition. In purine nucleotides, intracellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations rapidly and significantly decreased after the treatment with ischemia. No remarkable differences were observed in other purine nucleotides, with the exception of inosine monophosphate (IMP) and extracellular hypoxanthine levels, both of which increased significantly during the ischemia. The lactate dehydrogenase activity in culture supernatant of C2C12 myotubes increased significantly from 2 to 4 hr after the ischemia. On the generation of free radicals, no spectrum was detected in supernatants throughout the observation period, whereas supernatant TBARS concentration increased rapidly and significantly after the ischemia. The relative intensity of [Ca2+]i significantly increased after the ischemia. On the fragmented deoxyribonucleic acid(DNA), no TUNEL positive cells was detected in C2C12 myotubes after 1 hr of the ischemia, however the positive cell percentage subsequently increased. From these results, it was suggested that the ischemic condition induced changes of membrane permeability and increase of [Ca2+]i, both of which lead to cell membrane damage, although a free radical generation was not detected. The ischemic condition also induced the release of substrate hypoxanthine for free radical generation and might initiate the apoptotic pathway in C2C12 myotubes.Facultad de Ciencias Veterinaria

Increase of Na+ gradient-dependent L-glutamate and L-aspartate transport in high K+ dog erythrocytes associated with high activity of (Na+, K+)-ATPase.

As reported previously, some dogs possess red cells characterized by low Na+, high K+ concentrations, and high activity of (Na+, K+)-ATPase, although normal dog red cells contain low K+, high Na+, and lack (Na+, K+)-ATPase. Furthermore, these red cells show increased activities of L-glutamate and L-aspartate transport, resulting in high accumulations of such amino acids in their cells. The present study demonstrated: (i) Na+ gradient-dependent L-glutamate and L-aspartate transport in the high K+ and low K+ red cells were dominated by a saturable component obeying Michaelis-Menten kinetics. Although no difference of the Km values was observed between the high K+ and low K+ cells, the Vmax values for both amino acids' transport in the high K+ cells were about three times those of low ones. (ii) L- and D-aspartate, but not D-glutamate, competitively inhibited L-glutamate transport in both types of the cells. (iii) Ouabain decreased the uptake of the amino acids in the high K+ dog red cells, whereas it was not effective on those in the low K+ cells. (iv) The ATP-treated high K+ cells [(K+]i not equal to [K+]o, [Na+]i greater than [Na+]o) showed a marked decrease of both amino acids' uptake rate, which was almost the same as that of the low K+ cells. (v) Valinomycin stimulated the amino acids' transport in both of the high K+ and the ATP-treated low K+ cells [( K+]i greater than [K+]o, [Na+]o), suggesting that the transport system of L-glutamate and L-aspartate in both types of the cells might be electrogenic. These results indicate that the increased transport activity in the high K+ dog red cells was a secondary consequence of the Na+ concentration gradient created by (Na+, K+)-ATPase

(Na,K)-ATPase and Ouabain binding in reticulocytes from dogs with high K and low K erythrocytes and their changes during maturation.

The present study demonstrated that dog reticulocytes had considerable amounts of (Na,K)-ATPase, but lost it rapidly during maturation into erythrocytes. Furthermore, reticulocytes from dogs possessing erythrocytes characterized with high (Na,K)-ATPase activity and high K, low Na concentrations (HK dogs; Maede, Y., Inaba, M., and Taniguchi, N. (1983) Blood 61,493-499) had more ouabain binding sites than cells from normal dogs (LK dogs). Our results were as follows: i) The maximal binding capacities (Bmax) for ouabain binding at equilibrium were approximately 0 and 1,500 binding sites/cell in LK and HK dog erythrocytes, respectively. ii) Reticulocytes from LK dogs possess approximately 5,700 ouabain binding sites/cell. iii) The Bmax value for ouabain in HK reticulocytes was about 10,000 sites/cell, being 2-fold that in LK reticulocytes. iv) Ouabain-sensitive fluxes of 24Na and 42K in each type of reticulocyte were compatible with the number of ouabain binding sites on the cells. v) Ouabain binding capacity, as well as (Na,K)-ATPase activity, in the reticulocytes from LK dogs fell rapidly to nearly zero during the maturation into erythrocytes. vi) Although reticulocytes from HK dogs also showed a similar regression of (Na,K)-ATPase during maturation, they retained a certain number of ouabain binding sites even after maturation, resulting in the high activity of (Na,K)-ATPase in HK erythrocyte membrane

Na,K-ATPase in dog red cells. Immunological identification and maturation-associated degradation by the proteolytic system.

The Na,K-ATPase of red cells from high K+ and low K+ dogs was studied immunologically by using antibodies raised against dog kidney enzyme. Anti-alpha subunit IgGs, which also recognized alpha (+) from brain enzyme, identified the larger subunit of erythrocyte Na,K-ATPase as a homogeneous polypeptide with Mr = 96,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by immunoblotting. In addition, erythrocyte Na,K-ATPase, purified by immunoaffinity chromatography on a monoclonal antibody-coupled column, showed the identity of its polypeptide composition to that of the renal enzyme. Furthermore, it was shown that reticulocyte lysates from high K+ and low K+ dogs substantially degraded 125I-Bolton-Hunter reagent-labeled Na,K-ATPase. This degradation of the enzyme protein was significantly enhanced by the addition of ATP and Mg2+. These results indicate that dog reticulocytes possess some mechanism for protein breakdown involving an ATP-dependent proteolytic system, resulting in the dramatic breakdown of Na,K-ATPase activity during dog reticulocyte maturation into erythrocytes (Maede, Y., and Inaba, M. (1985) J. Biol. Chem. 260, 3337-3343)

Increase of Na-K-ATPase activity, glutamate, and aspartate uptake in dog erythrocytes associated with hereditary high accumulation of GSH, glutamate, glutamine, and aspartate.

We have found convincing evidence for the presence of Na-K-ATPase and high potassium (K) and low sodium (Na) concentrations in the erythrocytes of some dogs associated with hereditary high concentrations of erythrocyte glutathione and some amino acids, glutamate, glutamine, and aspartate. The Na-K-ATPase activity of the erythrocyte membranes of the dogs was about 3 times that of human erythrocyte membranes, whereas the enzyme activity was not detected in control dogs with a normal level of blood glutathione. The Michaelis constant of the enzyme for ATP (Km ATP) was 6.6 X 10(-3)M in the dogs' erythrocytes and 5.0 X 10(-4)M in the human erythrocytes. The concentration of K in the erythrocytes in the dogs examined was about 11 times that of the controls, whereas the erythrocyte Na concentration in the dogs was about one-third that of the controls. The concentrations of K and Na in the plasma of the dogs were equal to those of the controls. Furthermore, L-3H-glutamate and L-3H-aspartate uptake by those cells with high activity of Na-K-ATPase greatly increased, while L-3H-glutamine uptake was unchanged. It appeared that Na+ and K+ gradients created by Na-K-ATPase across the cell membrane might stimulate glutamate and aspartate uptake by the cells, thus causing the high accumulation of such amino acids in the cells

DETECTION OF EQUINE IMMUNOGLOBULIN-SECRETING CELLS BY A PLAQUE ASSAY

A protein A-hemolytic plaque assay was applied to detect immunoglobulin (Ig)-producing cells in horse peripheral blood, using pokeweed mitogen as a B lymphocyte activator. A maximum number of Ig-secreting cells was obtained when horse peripheral blood lymphocytes were cultured in a medium containing horse serum. The number of Ig-secreting cells in young horses (2 years old) was lower than that in adult horses (6 to 23 years old). In addition, the plaque formation was unchanged from blood samples kept at 4℃ for 24 hours, while blood samples kept for 72 hours did not yield plaques. These results indicate that the plaque assay is a reliable and useful method for detecting Ig-secreting cells in the peripheral blood of the horse

The forced aggresome formation of a bovine anion exchanger 1 (AE1) mutant through association with ΔF508-cystic fibrosis transmembrane conductance regulator upon proteasome inhibition in HEK293 cells

The endoplasmic reticulum (ER)-associated degradation of various polytopic proteins, involving the most common mutant of cystic fibrosis transmembrane-conductance regulator (CFTR), ΔF508-CFTR, involves retrotranslocation of the polypeptide into the cytosol, leading to aggresome formation when the proteasome activity is attenuated. By contrast, an R664X nonsense mutant of the bovine anion exchanger 1 (AE1) is retained in the ER and does not form aggresomes upon proteasome inhibition in transfected HEK293 cells. Here, we report that R664X AE1 formed a large cytoplasmic aggregate when cells co-transfected with enhanced green fluorescence protein (EGFP)-ΔF508-CFTR were exposed to the proteasome inhibitor lactacystin. R664X AE1 and EGFP-ΔF508-CFTR showed co-localization in the aggregates and signals of which coincided with γ-tubulin and were caged by vimentin at the pericentriolar locus, demonstrating aggresome formation. On the other hand, EGFP-AnkN90, consisting of the N-terminal AE1 binding domain of ankyrin, a ytoplasmic protein, also exhibited co-localization with R664X AE1, but was found throughout the ER. Moreover, R664X-mutant protein was specifically immunoprecipitated with EGFP-ΔF508-CFTR from the cells co-expressing these proteins. These findings indicate that R664X AE1 is forcibly extracted from the ER to reside in aggresomes through association with ΔF508-CFTR