Biomedical subjects
Y Kijima
Publications and source records attributed to Y Kijima.
A cardiac clathrin assembly protein forms a potassium channel in planar lipid bilayers.
A novel clathrin assembly protein (designated cardiac AP-3) has been isolated from dog heart which forms a K+ channel in planar lipid bilayers. AP-3 facilitated the in vitro formation of clathrin cages, which is diagnostic for clathrin assembly proteins. AP-3 consists mainly of 100-, 97-, and 55-kDa bands. A GTP-binding protein of approximately 25 kDa also co-purifies. The 100-kDa band was recognized by a monoclonal antibody to the gamma-adaptin of bovine brain clathrin assembly protein AP-1. A polyclonal antibody to the approximately 100-kDa doublet (alpha- and beta-adaptins) of bovine brain AP-2 did not cross-react with the purified protein. Western blot analysis of cardiac subcellular fractions showed that anti-AP-1 immunoreactivity was strongest in a sarcolemma-enriched fraction. Little immunoreactivity was detected in other cardiac subfractions, including sarcoplasmic reticulum, intercalated discs, and mitochondria. When reconstituted into planar lipid bilayers, AP-3 displays ion channel activity. Permeability ratios were PK/PCl approximately 16 and PK/PNa approximately 3, indicating a cation-selective channel somewhat selective for K+ versus Na+. The K+ channel displays several subconductance states (9 and 12 picosiemens in the main) and was blocked by CaCl2 (mM), inositol 1,3,4,5-tetrakisphosphate (20 microM), inositol 1,4,5-trisphosphate) (40 microM), and guanosine 5'-O-(3-thiotrisphosphate) (mM). Thus, the cardiac AP-3 appears to act as a K+ channel modulated by inositol polyphosphates and a small GTP-binding protein.
Different intracellular localization of inositol 1,4,5-trisphosphate and ryanodine receptors in cardiomyocytes.
The ryanodine and inositol 1,4,5-trisphosphate (IP3) receptors have previously been found to be intracellular Ca2+ release channels characterized by their large size and 4-fold symmetry. In this study, cardiomyocytes are found to have a different intracellular localization for the two receptors. At the level of light microscopy, the IP3 receptor is immunolocalized in rat ventricular cardiomyocytes at the region of the intercalated discs. By contrast, immunoreactivity of the ryanodine receptor is observed as transverse bands throughout the length of the cardiomyocyte, coincident with the triad junction at the I-bands. At the level of electron microscopy, immunogold particles directed to the IP3 receptor specifically decorate the intercalated discs of rat ventricular and atrial cardiomyocytes, preferentially at the fascia adherens. Binding of [3H] IP3 and [3H]ryanodine were measured in cardiac subcellular fractions. IP3 binding is enriched in a fraction containing intercalated discs. Little or no IP3 binding was detected in longitudinal sarcoplasmic reticulum (SR), junctional SR, sarcolemma, mitochondria, and submitochondrial vesicles. Ryanodine binding is the highest in junctional SR. We conclude that the IP3 receptor is present in ventricular and atrial cardiomyocytes and localized at the region of the intercalated discs. These results suggest a possible role of the IP3 receptor in Ca2+ entry through intercalated discs and/or intercellular signaling between cardiomyocytes.
Two types of inositol trisphosphate binding in cardiac microsomes.
Two distinct types of [3H]IP3 binding were found in canine cardiac microsomes with high (Kd = 21 nM, Bmax = 0.66 pmol/mg) and low affinity (Kd = 230 nM, Bmax = 2.9 pmol/mg). Also found were low affinity [3H]IP4 binding (Kd = 190 nM, Bmax = 4.5 pmol/mg) and high affinity [3H]IP6 binding (Kd = 10 nM, Bmax = 4.9 pmol/mg). The rank order of potency to displace these radioligands indicates that binding of IP3 and IP6 is ligand-specific. Sucrose gradient centrifugation of the detergent-solubilized cardiac microsomes indicates that the molecular size of the cardiac high affinity IP3 receptor is similar to that of the aortic smooth muscle IP3 receptor and smaller than that of the ryanodine receptor which migrates more rapidly. The IP4 and IP6 binding migrates more slowly than the IP3 receptor.
[Report of a case with aortic regurgitation in progressive systemic sclerosis].
Aortic valve lesions in progressive systemic sclerosis (PSS) are very uncommon. To our knowledge, aortic regurgitation (AR) associated with PSS has not been reported previously. We would like to report the case of a 58-year-old woman who had PSS with AR due to Raynaud's symptom, fever, positive ANA, accelerated ESR, and diastolic blowing murmur along the left sternal border. After treatment with adreno-cortico steroid and an immunosuppressive agent, the patient improved serologically and symptomatically. However, she was later admitted to our hospital again due to heart failure with progressive AR. She died of refractory heart failure with severe AR and tricuspid regurgitation (TR). The former was caused by aortic cusp lesions and the latter by pulmonary hypertension. An autopsy confirmed the diagnosis of PSS, which was found to have involved the heart, lungs and pancreas. Vasculitis with infiltration and fibrotic changes were noted in these organs. Moreover, there were fibrotic thickenings and shortenings in the aortic cusps with cell infiltration. There were no indications of rheumatic disease. These results suggest that the cause of our patient's aortic valve disease may have been PSS vasculitis.
Drug action of thapsigargin on the Ca2+ pump protein of sarcoplasmic reticulum.
Thapsigargin is found to be a potent inhibitor of the intracellular Ca2+ pump proteins from skeletal muscle sarcoplasmic reticulum (SR), cardiac SR, and brain microsomes. For skeletal muscle SR, the molar ratio of thapsigargin to Ca2+ pump protein for complete inhibition (MRc) of the Ca2+ loading rate, Ca(2+)-dependent ATPase activity, and formation of phosphorylated intermediate (EP) was approximately 1. When the Ca2+ pump protein of low affinity to Ca2+ (E2 state) was pretreated with thapsigargin, ATP and Ca2+ binding to the Ca2+ pump protein was completely inhibited. In the presence of Ca2+ (E1 state), Ca2+ pump protein was protected from inactivation by thapsigargin with respect to Ca2+ binding and EP formation. The MRc for brain microsomes, which mediate Ca2+ uptake into intracellular (inositol 1,4,5-trisphosphate-releasable) Ca2+ pools, is likewise stoichiometric. Approximately 30% of Ca2+ loading activity of brain microsomes was insensitive to thapsigargin, indicating the presence of other Ca2+ pumping system(s). The MRc for heart is 3.8, indicating that the Ca2+ pump of cardiac SR is less sensitive to thapsigargin. Phosphorylation of cardiac SR with protein kinase A increased the sensitivity to thapsigargin to MRc of 2.8. In summary, we find that: 1) thapsigargin is the most effective inhibitor of the Ca2+ pump protein of intracellular membranes (SR and endoplasmic reticulum); 2) its primary inhibitory action appears to inactivate the E2 form of the enzyme preferentially; 3) cardiac SR shows lesser sensitivity to thapsigargin than skeletal muscle SR and brain microsomes; protein kinase A treatment of cardiac SR enhances the sensitivity to the drug.
Effects of monoclonal antibody against phospholamban on calcium pump ATPase of cardiac sarcoplasmic reticulum.
A monoclonal antibody against phospholamban has been reported to increase Ca2+ uptake by cardiac sarcoplasmic reticulum. We compared the effect of this antibody on Ca2+ pump ATPase activity of cardiac sarcoplasmic reticulum vesicles to the effect of cAMP-dependent phosphorylation of phospholamban. The antibody markedly stimulated the Ca(2+)-dependent ATPase activity in parallel to the increase in Ca2+ uptake by cardiac sarcoplasmic reticulum. When the Ca(2+)-dependent profile of the ATPase activity was compared, the KCa was shifted from 1.24 to 0.62 microM by the antibody, whereas cAMP-dependent phosphorylation of phospholamban shifted the KCa to 0.84 microM. When cardiac sarcoplasmic reticulum vesicles were treated with both cAMP-dependent protein kinase and the antibody, the stimulation was the same as that with the antibody alone. Thus, the Ca2+ pump ATPase seems to be fully activated by the antibody. The stoichiometry between Ca2+ uptake and ATPase rate was around 1 and no significant change was observed by the treatment with the antibody. Therefore, the stimulation of Ca2+ uptake of cardiac sarcoplasmic reticulum by the antibody occurred by the stimulation of Ca2+ pump ATPase, not by other mechanisms such as channel activity of phospholamban. These results indicate that the binding of the antibody to phospholamban produces essentially the same mode of action on Ca2+ pump ATPase as that of phospholamban phosphorylation. The antibody and phospholamban phosphorylation appear to release the inhibitory action of phospholamban on Ca2+ pump ATPase, resulting in the stimulation of Ca2+ pump.
Molecular weight determination of phospholamban oligomer in the presence of sodium dodecyl sulfate: application of low-angle laser light scattering photometry.
The number of polypeptides constituting the oligomeric structure of canine phospholamban (a putative regulator of Ca(2+)-ATPase of cardiac sarcoplasmic reticulum) stable even in the presence of sodium dodecyl sulfate was estimated through determination of the molecular weight of the oligomer. Owing to the small molecular size, the low UV-absorptivity and the limited availability, the molecular weight determination required very sophisticated application of the following technique, used as the only recourse: low-angle laser light scattering measurement combined with high-performance gel chromatography. The molecular weight of phospholamban oligomer was found to be 30,400 and the number of subunits was concluded to be five after correction for the dependence of the apparent molecular weights on the protein concentration.
[Acute renal cortical necrosis and renal papillary necrosis].
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Human liver manganese superoxide dismutase. Purification and crystallization, subunit association and sulfhydryl reactivity.
Manganese superoxide dismutase (Mn-SOD) has been purified with a high yield (320 mg) from human liver (2 kg) and crystallized. Low-angle laser light scattering of the enzyme has shown that native enzyme is a tetrametic form. Four of the eight cysteine residues in the tetramer reacted with 5,5'-dithiobis(2-nitrobenzoic acid) or with iodoacetamide. The others were only reactive in protein heated with SDS or urea after reduction with dithiothreitol or 2-mercaptoethanol. The reactive sulfhydryl group was found to be located at Cys196 by amino acid sequence analysis of Nbs2-reactive peptides isolated by activated thiol-Sepharose covalent chromatography. Incubation of Mn-SOD in 1% SDS for 2 or 3 days at 25 degrees C or 5 min at 100 degrees C gave material showing two prominent components on polyacrylamide gel electrophoresis in the presence of 0.1% SDS. The major component had a molecular mass of 23 kDa; the other, 25 kDa. Reduction of the protein by dithiothreitol or 2-mercaptoethanol heated in SDS produced only the 25-kDa monomer species. Essentially, no thiol groups were detected in the 23-kDa form, in which two cysteine residues appear to have been oxidized to form an intrasubunit disulfide. This indicates that Cys196 has a reactive sulfhydryl and appears to be a likely candidate for a mixed disulfide formation in vivo.
Protein-protein interaction of detergent-solubilized Ca2(+)-ATPase during ATP hydrolysis analyzed by low-angle laser light scattering photometry coupled with high-performance gel chromatography.
Protein-protein interaction of detergent-solubilized Ca2(+)-ATPase was examined, employing low-angle laser light scattering photometry coupled with high-performance gel chromatography. When solubilized with octa(ethylene glycol) mono-n-dodecyl ether (C12E8) and chromatographed in the presence of 0.3 mg/ml C12E8, the Ca2(+)-ATPase emerged as a single peak with an intermediate molecular weight between the monomer and the dimer, showing a dissociation-association equilibrium of the two components. In the presence of 50 micrograms/ml phosphatidylcholine and 0.3 mg/ml C12E8 at 0 degrees C, the Ca2(+)-ATPase (0.8 mg) emerged as the two distinct components with molecular weights of 125,000 +/- 2100 (n = 3) and 211 300 +/- 7300 (n = 3), indicating that there was no rapid interconversion between the monomer and the dimer. Under the latter conditions, addition of ATP induced fusion of two components. The apparent molecular weight of the fused peak shifted from the monomer to the dimer as the amount of protein increased. Addition of ADP or adenosine 5'-(beta, gamma-methylene triphosphate), however, did not induce such fusion of the peaks. The ATP-induced fusion of the peaks was not observed either in 5 mM CaCl2, the conditions in which the rate of ATP hydrolysis was extremely slow. Thus, the solubilized Ca2(+)-ATPase underwent a rapid interconversion between the monomer and the dimer during ATP hydrolysis. These results suggest that the protein-protein interaction during ATP hydrolysis is an intrinsic nature of Ca2(+)-ATPase and that such interaction may be important for Ca2+ transport by Ca2(+)-ATPase in the sarcoplasmic reticulum membranes.
Molecular structure and function of phospholamban: the regulatory protein of calcium pump in cardiac sarcoplasmic reticulum.
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The endoscopic intratumor administration of OK-432 in gastric cancer unsuitable for surgery.
In eleven patients with gastric cancer who could not be operated on because of advanced age, refusal of surgery, or the presence of complications, the streptococcal preparation OK-432 was administered, both intradermally and by direct injection into the tumor under endoscopic guidance. Via gastric x-ray and endoscopic examinations, the tumor was observed to disappear in two cases-one advanced cancer and one early gastric cancer endoscopically. Particularly in the latter case repeated biopsies revealed no evidence of cancer cells. All patients developed fever after intratumor injection, but in no case was it necessary to discontinue administration, and no other serious side effects were noted. The endoscopic injection of OK-432 appears to be a safe and useful form of therapy for gastric cancer unsuitable for surgery.
[A case of virilizing Leydig cell tumor of the accessory adrenal].
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Anabolic steroid-associated hypogonadism in male hemodialysis patients.
Hypogonadism in male hemodialysis patients has been previously reported. However, its precise pathogenesis has not yet been clarified. Mepitiostane and nandrolone decanoate are anabolic steroids prescribed for uremic anemia, and those may possibly exacerbate uremic gonadal damage. We studied the influences of these steroids on male gonadal function. Seventy-six hemodialysis patients were selected and examined for levels of luteinizing hormone (LH), follicular stimulating hormone (FSH), total testosterone, and prolactin. Twenty-three patients who received anabolic steroids showed lower testosterone values (205.2 +/- 35.6 ng/dl) than did patients without these steroids (449.7 +/- 21.3 ng/dl). Gonadotropins and prolactin showed no significant differences between the patients with and without the steroids. The testosterone values of three patients with mepitiostane increased after they stopped taking steroids. One patient suffering from complete aspermia recovered (sperm count: 0/ml to 1300 x 10(4)/ml) after discontinuation of mepitiostane and administration of human chorionic gonadotropin (HCG). This clinical study suggests that some anabolic steroids play a role in uremic hypogonadism; thus mepitiostane or its analogues should be carefully prescribed for young male patients.
[The role of phospholamban in cardiac sarcoplasmic reticulum].
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Comparison of binding characteristics of human and bovine serum albumins with benzoates over a wide range of concentration.
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