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Biomedical subjects

H Kojima

Publications and source records attributed to H Kojima.

At least 379 records · Page 21Linked to original sources
PubMed1995

Modulation of platelet activation in vitro by thrombopoietin.

Effect of human recombinant thrombopoietin (TPO) on platelet activation in vitro was studied. Although TPO itself did not cause platelet aggregation, it upregulated ADP-induced aggregation, especially the second wave of aggregation. This effect was dose-dependent for up to 5 ng/ml of TPO. When platelets were activated by epinephrine, collagen, or alpha-thrombin, similar effect was observed. However, TPO did not affect A23187- or PMA-induced aggregation, suggesting that TPO may have modulated the signal transduction pathway upstream of inositol 1,4,5-trisphosphate and diacylglycerol production. TPO also upregulated thrombin-induced alpha-granule secretion. To clarify the involvement of protein tyrosine phosphorylation, platelets were activated by TPO and/or suboptimal concentration of ADP, then tyrosine phosphorylation was detected by immunoblot analysis, using anti-phosphotyrosine monoclonal antibody. TPO by itself caused significant tyrosine phosphorylation of 146, 130, 122, 108, 97, 94, and 88 kDa proteins. Further, by using antibodies against signal transduction molecules for immunoprecipitation, we observed the significant tyrosine phosphorylation in Jak2 and Tyk2 molecules after TPO-stimulation. The results of the present experiment clearly indicate that TPO directly activated platelets and modulated intracellular signal transduction pathway.

Blood Proteins↗
PubMed1994

Direct measurement of stiffness of single actin filaments with and without tropomyosin by in vitro nanomanipulation.

In order to explain the molecular mechanism of muscle contraction, it is crucial to know the distribution of the sarcomere compliance of active muscle. Here, we directly measure the stiffness of single actin filaments with and without tropomyosin, using a recently developed technique for nanomanipulation of single actin filaments with microneedles. The results show that the stiffness for 1-micron-long actin filaments with and without tropomyosin is 65.3 +/- 6.3 and 43.7 +/- 4.6 pN/nm, respectively. When the distribution of crossbridge forces along the actin filament is taken into account, the elongation of a 1-micron-long thin filament during development of isometric contraction is calculated to be approximately 0.23%. The time constant of force in response to a sudden length change is < 0.2 ms, indicating that the viscoelasticity is negligible in the millisecond time range. These results suggest that approximately 50% of the sarcomere compliance of active muscle is due to extensibility of the thin filaments.

Actins↗
PubMed1994

Comparison of neuronal nicotinic receptors in rat sympathetic neurones with subunit pairs expressed in Xenopus oocytes.

1. The agonist sensitivity of nicotinic acetylcholine receptors in rat superior cervical ganglion (SCG) neurones was compared with that of cloned receptors expressed in Xenopus oocytes by pairwise injections of alpha 3-beta 2 or alpha 3-beta 4 neuronal nicotinic subunit combinations. 2. Agonist responses in rat SCG neurones indicated that cytisine was the most potent agonist and lobeline the least potent (rank order of potency: cytisine > dimethylphenylpiperazinium iodide (DMPP) > nicotine > ACh > carbachol > lobeline). 3. Receptors expressed in oocytes by injection of alpha 3 and beta 2 subunits had a relatively high sensitivity to DMPP and low sensitivity to cytisine (rank order of potency: DMPP > ACh > lobeline > carbachol > nicotine > cytisine), whereas receptors composed of alpha 3 and beta 4 subunits had a high sensitivity to cytisine and low sensitivity to DMPP (rank-order of potency: cytisine > nicotine approximately ACh > DMPP > carbachol > lobeline). 4. With the exception of responses to DMPP, agonist sensitivity measurements suggest that nicotinic receptors in the rat SCG are composed of alpha 3 and beta 4 subunits. The results are discussed in terms of the receptor subunit mRNAs known to be expressed in the rat SCG and previous evidence of functional heterogeneity of rat SCG nicotinic acetylcholine receptors.

Alkaloids↗
PubMed1994

E1A repression of IL-6-induced gene activation by blocking the assembly of IL-6 response element binding complexes.

Some viral products interfere with host antiviral defense mechanisms. Adenovirus E1A represses IFN signal transduction pathways which induces gene activation and an antiviral state. Both IFN and IL-6 activate Jak/Tyk protein tyrosine kinases and the STAT (signal transducer and activator of transcription) family proteins. We showed that 12S E1A repressed IL-6 signals activating the junB promoter and the two IL-6 response elements (REs), JRE-IL6 and type II IL-6 RE (also called acute phase response element), required for IL-6-induced activation of the junB promoter and the type II acute phase reactant genes, respectively, in hepatocytes. Conserved region 1 of the 12S E1A was responsible for the repression. Target molecules of the repression by E1A appeared to be IL-6-inducible DNA-binding proteins acting on the IL-6 REs. In a rat 3Y1 cell line stably expressing E1A, the levels of IL-6-induced IL-6 RE binding proteins were severely reduced compared with those in a parental 3Y1 cell line. Moreover, we found that the levels of the STAT family proteins including Stat1-alpha (p91), Stat1-beta (p84), Stat2 (p113), and Stat3 were decreased by the stable expression of adenovirus E1A. The E1A-induced reduction in the amount of DNA-binding proteins seemed to be partly responsible for the decreased transcriptional activity of the IL-6 RE-driven gene expression in response to IL-6. This repression mechanism may be applicable to the E1A repression of IFN-gamma-induced gene activation.

Adenovirus E1A Proteins↗
PubMed1994

Transcriptional activation of the IL-6 response element in the junB promoter is mediated by multiple Stat family proteins.

IL-6 signals activate an IL-6 response element in the junB promoter, JRE-IL6, in a Ras-independent manner. IL-6 rapidly induced a DNA-binding activity to the Ets binding site of JRE-IL6 (JEBS), one of necessary DNA motifs of the IL-6 response element. The IL-6-induced JEBS-binding activity was indistinguishable from those to acute phase response element (APRE) in both kinetics of induction and its DNA-binding specificity. Purified APRE binding factors (APRFs) from IL-6-stimulated rat liver were found to be composed of multiple Stat3-related proteins and Stat1. Moreover the purified APRFs specifically made a complex with JRE-IL6 with the same mobility as that observed in the crude extracts. These results indicate that an immediate early signal of IL-6 leading to activation of JRE-IL6 is mediated by STAT family transcription factors.

Animals↗
PubMed1994

Single-molecule analysis of the actomyosin motor using nano-manipulation.

The elementary events in energy transduction by the actomyosin motor, driven by ATP hydrolysis, were directly recorded from multiple and single molecules using a recently developed technique for nano-manipulation of single actin filaments by a microneedle. In order to avoid the effects of random orientation of myosin and association of myosin with an artificial substrate in the surface motility assay, we used single myosin-rod cofilaments with various ratios. Distinct actomyosin attachment, force generation (the power stroke) and detachment events were detected at a very low myosin: rod ratio. At high load, one power stroke generated 5-6 pN peak force and 2.3 pN force averaged over the cycle, which were compatible with those deduced from noise analysis of force fluctuations caused by multiple molecules. As the load was reduced, the length of the power stroke increased. At near zero load, the length of a power stroke was approximately 17 nm. The results suggested that an ATPase cycle produces one power stroke at high load and many ones at low load.

Actins↗
PubMed1994

Capillary blood flow velocity measurements in cystoid macular edema with the scanning laser ophthalmoscope.

Using a scanning laser ophthalmoscope, we calculated the velocity of retinal blood flow in a juxta-foveolar capillary during the course of cystoid macular edema after partial central retinal vein occlusion in a 53-year-old woman. The mean velocity of the fluorescent dots in the macular capillary of the right eye with cystoid macular edema was 1.59 +/- 0.08 mm/sec at the initial examination. Despite the systemic administration of indomethacin (75 mg/day for three weeks), best-corrected visual acuity decreased from 20/30 to 20/70, and the velocity became 0.82 +/- 0.13 mm/sec. Prednisolone (30 mg/day orally for one week) improved the cystoid macular edema, and the velocity was 0.96 +/- 0.06 mm/sec 12 days after initiation of the drug. The velocity gradually improved; one year later it was 1.65 +/- 0.17 mm/sec and visual acuity was 20/22. Velocity in the left eye, which did not have cystoid macular edema, was 2.16 +/- 0.16 mm/sec. Thus, scanning laser ophthalmoscopy proved useful for measuring the velocity of retinal blood flow.

Blood Flow Velocity↗
PubMed1994

Mechanism of tracheoesophageal shunt phonation.

OBJECTIVE: To elucidate the phonatory mechanism of tracheoesophageal shunt speech after total laryngectomy, we examined the dynamics and origin of neoglottis in tracheoesophageal shunt speakers. DESIGN: We conducted the videofluoroscopic, strobofiberscopic, and electromyographic studies of the pharyngoesophageal segment in tracheoesophageal shunt photonation. SETTING: Academic referral medical center. PATIENTS: Twenty-five tracheoesophageal shunt speakers were examined. RESULTS: Videofluorescopic and fiberscopic examinations showed two bulges in the pharyngeoesophageal segment. The upper bulge was revealed to be the sound source of tracheoesophageal shunt speech by the stroboscopic examination; anteroposterior and undulating regular movements were observed. Electromyographic study elucidated the contribution of muscle contraction to the two bulges; the upper bulge is formed by the thyropharyngeal muscle, whereas the lower bulge corresponds to the cricopharyngeal muscle. CONCLUSION: The neoglottis was considered to be formed by the stenotic portion due to thyropharyngeal muscle contraction and mucosal vibration due to expiratory airflow. This new understanding of the phonatory mechanism will be indispensable in the treatment of cases with failing shunt speech.

Aged↗
PubMed1994

Cysteinyl leukotrienes in the urine of patients with liver diseases.

The significance of cysteinyl leukotrienes was investigated in patients with liver diseases by measurements of leukotriene E4 and N-acetyl-leukotriene E4 in urine. A marked increase of renal cysteinyl leukotriene excretion was observed in patients with cirrhosis without and with ascites, intrahepatic cholestasis, and obstructive jaundice as compared with healthy subjects (leukotriene E4: means 82, 264, 221 and 142 versus 40 nmol/mol creatinine, respectively; N-acetyl-leukotriene E4: means 25, 64, 61 and 47 versus 13 nmol/mol creatinine, respectively). The urinary concentration of leukotriene E4 was positively correlated with the one of N-acetyl-leukotriene E4 (r = 0.81, p < 0.001). In patients with cirrhosis, the excretion of cysteinyl leukotrienes was strongly increased in patients in Child-Turcotte stage C as compared with those in Child-Turcotte stages A and B. In patients with intrahepatic cholestasis and in those with obstructive jaundice, the excretion of leukotriene E4 plus N-acetyl-leukotriene E4 was positively correlated with total serum bilirubin. In patients with cirrhosis and in those with obstructive jaundice, the cysteinyl leukotrienes in urine were negatively correlated with creatinine clearance. The elevated renal excretion of cysteinyl leukotrienes decreased after biliary drainage in patients with obstructive jaundice. These data support the concept that increased urinary excretion of cysteinyl leukotrienes in patients with cirrhosis is due to a reduced functional liver mass and that in patients with cholestasis it is mainly due to an impaired elimination into the biliary tract that results in a diversion to renal excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗