Biomedical subjects

J Kawahara

Publications and source records attributed to J Kawahara.

At least 19 recordsLinked to original sources

PubMed2000

Retinoblastoma protein phosphorylation via PI 3-kinase and mTOR pathway regulates adipocyte differentiation.

In the early phase of adipocyte differentiation, transient increase of DNA synthesis, called clonal expansion, and transient hyperphosphorylation of retinoblastoma protein (Rb) are observed. We investigated the role of these phenomena in insulin-induced adipocyte differentiation of 3T3-L1 cells. Insulin-induced clonal expansion, Rb phosphorylation and adipocyte differentiation were all inhibited by the PI 3-kinase inhibitors and rapamycin, but not the MEK inhibitor, whereas the MEK inhibitor, but not PI 3-kinase inhibitors or rapamycin, decreased c-fos induction. We conclude that insulin induces hyperphosphorylation of Rb via PI 3-kinase and mTOR dependent pathway, which promotes clonal expansion and adipocyte differentiation of 3T3-L1 cells.

1-Methyl-3-isobutylxanthine↗

PubMed2000

Pseudogap formation in the intermetallic compounds (Fe1-xVx)3Al

Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0</=x</=0.33) reveal that their density of states around the Fermi energy ( E(F)) is strongly reduced as x is increased. In particular, Fe2VAl ( x = 0.33) has a deep, well-developed pseudogap of 0.1-0.2 eV at E(F) and a small density ( approximately 5x10(20) cm(-3)) of carriers, which is highly unusual for intermetallic compounds. It is shown that the pseudogap results from the band structure of Fe2VAl, rather than from temperature-dependent correlation effects. Based on the present results, we propose a simple model that consistently explains both the semiconductorlike transport and the metallic photoemission results previously observed for Fe2VAl.

Journal Article↗

PubMed2000

A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1.

Insulin receptor substrate-1 (IRS-1) is a major substrate of the insulin receptor and acts as a docking protein for Src homology 2 domain containing signaling molecules that mediate many of the pleiotropic actions of insulin. Insulin stimulation elicits serine/threonine phosphorylation of IRS-1, which produces a mobility shift on SDS-PAGE, followed by degradation of IRS-1 after prolonged stimulation. We investigated the molecular mechanisms and the functional consequences of these phenomena in 3T3-L1 adipocytes. PI 3-kinase inhibitors or rapamycin, but not the MEK inhibitor, blocked both the insulin-induced electrophoretic mobility shift and degradation of IRS-1. Adenovirus-mediated expression of a membrane-targeted form of the p110 subunit of phosphatidylinositol (PI) 3-kinase (p110CAAX) induced a mobility shift and degradation of IRS-1, both of which were inhibited by rapamycin. Lactacystin, a specific proteasome inhibitor, inhibited insulin-induced degradation of IRS-1 without any effect on its electrophoretic mobility. Inhibition of the mobility shift did not significantly affect tyrosine phosphorylation of IRS-1 or downstream insulin signaling. In contrast, blockade of IRS-1 degradation resulted in sustained activation of Akt, p70 S6 kinase, and mitogen-activated protein (MAP) kinase during prolonged insulin treatment. These results indicate that insulin-induced serine/threonine phosphorylation and degradation of IRS-1 are mediated by a rapamycin-sensitive pathway, which is downstream of PI 3-kinase and independent of ras/MAP kinase. The pathway leads to degradation of IRS-1 by the proteasome, which plays a major role in down-regulation of certain insulin actions during prolonged stimulation.

3T3 Cells↗

PubMed2000

Effects of pegylated recombinant human megakaryocyte growth and development factor on 5-fluorouracil-induced thrombocytopenia in balloon-injured rats.

We examined whether pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) affected 5-fluorouracil-induced thrombocytopenia without inducing more severe intimal thickening after injury to rat carotid arteries. Rat carotid arteries were injured using a balloon catheter on day 0. 5-Fluorouracil (100 mg kg(-1)) or vehicle was intravenously administered on day 1 in balloon-injured rats. PEG-rHuMGDF (100 microg kg(-1)) or vehicle was intravenously administered once a day on days 1-5 to balloon-injured rats given 5-fluorouracil or vehicle. 5-Fluorouracil (100 mg kg(-1), i.v.) caused a significant decrease in the platelet count from day 3 and peaked on days 7-9 in balloon-injured rats. PEG-rHuMGDF (100 microg kg(-1), i.v.) reduced this decrease on days 9 and 11. The administration of PEG-rHuMGDF did not accelerate the intimal thickening of balloon-injured arteries in rats treated with 5-fluorouracil compared with control balloon-injured rats. PEG-rHuMGDF did not increase plasma tumour growth factor-beta1 (TGF-beta1) from days 0-9 in balloon-injured rats compared with control balloon-injured rats. These results suggest that PEG-rHuMGDF ameliorated 5-fluorouracil-induced thrombocytopenia without accelerating the intimal thickening of balloon-injured arteries.

Animals↗

PubMed1999

Antihypertensive properties of KRN4884, a novel long-lasting potassium channel opener.

The antihypertensive action of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine ), a newly synthesized 3-pyridine derivative was examined in conscious spontaneously hypertensive rats (SHRs). A single administration of KRN4884 (0.5, 1.5 mg/kg, p.o.) produced a dose-dependent and long-lasting antihypertensive effect. The 7-day repeated administration of KRN4884 (0.5, 1.5 mg/kg, p.o.) did not diminish antihypertensive activity during the treatment period or induce rebound hypertension after the discontinuation of treatment. To examine the mechanism of the antihypertensive effect of KRN4884, we studied its vasorelaxing effects in rat isolated aortae precontracted with 25 mM KCl. Single application of KRN4884 showed a slower onset of inhibitory action than that of levcromakalim. KRN4884 was approximately 26-fold more potent than levcromakalim and 10-fold less potent than nilvadipine. KRN4884- and levcromakalim-induced vasorelaxation were antagonized by glibenclamide. Furthermore, we observed the recovery of the contraction inhibited by these drugs after repeated washing. The inhibitory effect of KRN4884 was restored only after four washes, whereas that of levcromakalim was completely restored after one wash. The nilvadipine-induced inhibitory effect was the most resistant to washing among these drugs. These results suggest that KRN4884 shows a long-lasting antihypertensive effect based on its potent potassium channel-opening action. The long-lasting action may be due to a slow association/dissociation with/from the binding sites on vascular smooth muscle.

Animals↗

PubMed1999

A mild transient decrease of peripheral red blood cell counts induced by a suprapharmacological dose of pegylated human megakaryocyte growth and development factor in rats.

Previous studies have shown that pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) at suprapharmacological dose induces a mild transient decrease of red blood cell counts according to thrombopoiesis in normal mice. To unravel the mechanism underlying this mild transient decrease of red blood cells, we have studied the effect of PEG-rHuMGDF on the circulating plasma and blood volume, and the serum biochemical parameters of anaemia and splenectomy. Also, we have performed histological studies of the bone marrow and the spleen of PEG-rHuMGDF-treated rats. PEG-rHuMGDF (300 microg kg(-1)]) or vehicle was subcutaneously administered to rats once a day for up to five days. From day 6 after the start of PEG-rHuMGDF administration, the platelet counts and plateletcrit levels were significantly increased, reaching peak values on day 10, and recovering to normal by day 20. The red blood cell counts and the haematocrit levels were significantly decreased on day 6 to 13. The decreases in red blood cell levels and haematocrit produced by PEG-rHuMGDF treatment were mild and had recovered by day 15. The plasma and blood volumes were significantly increased on day 10 in PEG-rHuMGDF-treated rats. No alteration of the serum biochemical parameters for anaemia, iron or total bilirubin, were observed on day 10. The histological examination on day 10 revealed a marked increase in megakaryocytes and a slight decrease in erythropoiesis in the bone marrow of rats that received PEG-rHuMGDF (300 microg kg(-1)). There was also a slight increase in splenic megakaryocytes and erythropoiesis. The decrease of red blood cells by PEG-rHuMGDF was not affected by splenectomy. These results suggest that the mild transient decrease of red blood cells induced by PEG-rHuMGDF treatment for up to five days is based mainly on the increases in the plasma and blood volume. These events are secondary changes due to the regulation of the excess production of megakaryocytes in the marrow and the peripheral platelets.

Anemia↗

PubMed1998

Acylamino acid-releasing enzyme from the thermophilic archaeon Pyrococcus horikoshii.

When the genome of the thermophilic archaeon Pyrococcus horikoshii was sequenced, a gene homologous to the mammalian gene for an acylamino acid-releasing enzyme (EC 3.4.19.1) was found in which the enzyme's proposed active residues were conserved. The P. horikoshii gene comprised an open reading frame of 1,896 base pairs with an ATG initiation codon and a TAG termination codon, encoding a 72,390-Da protein of 632 amino acid residues. This gene was overexpressed in Escherichia coli with the pET vector system, and the resulting enzyme showed the anticipated amino-terminal sequence and high hydrolytic activity for acylpeptides. This enzyme was concluded to be the first acylamino acid-releasing enzyme from an organism other than a eukaryotic cell. The existence of the enzyme in archaea suggests that the mechanisms of protein degradation or initiation of protein synthesis or both in archaea may be similar to those in eukaryotes. The enzyme was stable at 90 degreesC, with its optimum temperature over 90 degreesC. The specific activity of the enzyme increased 7-14-fold with heat treatment, suggesting the modification of the enzyme's structure for optimal hydrolytic activity by heating. This enzyme is expected to be useful for the removal of Nalpha-acylated residues in short peptide sequence analysis at high temperatures.

Amino Acid Sequence↗

PubMed1998

Effects of KRN4884 (a novel K+ channel opener), levcromakalim, nilvadipine and propranolol on endothelin-1-induced heart disorders in anesthetized rats.

The effects of KRN4884 (5-amino-N-[2-(2-chrolophenyl)ethyl]-N'-cyano-3-pyridinecarboxa midine), a novel K+ channel opener, on the electrocardiogram changes caused by the intracoronary administration of endothelin-1 (ET-1) were studied in anesthetized rats and compared with the effects of levcromakalim, a K+ channel opener; nilvadipine, a Ca2+ antagonist; and propranolol, a beta-adrenoceptor antagonist. KRN4884 (50 microg/kg, i.v.) and levcromakalim (300 microg/kg, i.v.) inhibited the ST segment elevation and the development of arrhythmias induced by ET-1 (5 microg, i.c.) and decreased the incidence of death. Nilvadipine (300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.) each prevented the ST segment elevation, but the suppressions of the occurrence of arrhythmias produced by nilvadipine and propranolol were less than that shown by KRN4884. KRN4884 (30 and 50 microg/kg, i.v.), levcromakalim (100 and 300 microg/kg, i.v.) and nilvadipine (100 and 300 microg/kg, i.v.) significantly decreased the mean blood pressure in a dose-dependent manner, but propranolol did not. The heart rate was decreased by nilvadipine (100 and 300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.), but was not affected by KRN4884 (30 and 50 microg/kg, i.v.) or levcromakalim (100 and 300 microg/kg, i.v.). These results suggest that pretreatments with KRN4884 and levcromakalim are more effective on ET-1-induced electrocardiogram changes than those with nilvadipine and propranolol.

Anesthesia↗

PubMed1997

KRN4884, a novel K channel opener: antihypertensive effects in conscious renal hypertensive dogs.

We examined the antihypertensive effects of KRN4884, 5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarbocamidine+ ++, in normotensive dogs, a high-renin model acute renal hypertensive dog (RHD), and a low-renin model chronic RHD in the conscious state, compared with levcromakalim and nilvadipine. KRN4884 decreased mean blood pressure (MBP) at a dose of 0.1 mg/kg p.o. in normotensive dogs and both RHDs. The decrease in MBP was greater in both RHDs than in normotensive dogs, and there were no significant differences between the two RHDs. A transient increase in heart rate (HR) accompanied the increase in MBP in all three types of dogs. In the chronic RHD, KRN4884 at doses of 0.05, 0.1, and 0.2 mg/kg produced a dose-dependent decrease in MBP. The antihypertensive effect of KRN4884 (0.1 mg/kg) was similar to those of levcromakalim (0.05 mg/kg) and nilvadipine (1.0 mg/kg) in magnitude and more prolonged than those of the compounds. The tachycardia induced by KRN4884 was similar to that induced by levcromakalim and was stronger than that induced by nilvadipine. In the 15-day repeated oral-administration study, KRN4884 (0.1 mg/kg) induced sustained hypotensive effects and transient increases in HR and plasma renin activity. No tolerance to the antihypertensive effect of KRN4884 was observed during a 15-day repeated dosing period. After withdrawal of KRN4884, no rebound phenomena in MBP and HR were observed. Neither the maximal concentration nor area under the curve (AUC) of KRN4884 in plasma were changed at days 1, 8, and 15. These data indicate that KRN4884 produces a strong and persistent antihypertensive response in both low-renin and high-renin models of RHD in a conscious state, which suggests that KRN4884 may be useful as an antihypertensive agent.

Animals↗

PubMed1997

In vitro and in vivo vasodilating effects of KRN4884, Ki1769 and Ki3005, pyridinecarboxamidine derivatives.

The vasodilating potencies and mechanism of action of a novel pyridinecarboxamidine derivative, KRN4884 [5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine ] were compared with those of Ki1769 [N-cyano-N'-(2-phenylethyl)-3-pyridinecarboxamidine] and Ki3005 [N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine] in rat isolated aortas and in anesthetized normotensive rats. In vitro. KRN4884 (10(-10)-10(-6) M). Ki1769 (10(-8)-10(-5) M) and Ki3005 (10(-10)-10(-6) M) produced concentration-dependent relaxations. KRN4884 was about 100- and 10-fold more potent than Ki1769 and Ki3005, respectively. The relaxant effects of these compounds were antagonized by glibenclamide. In vivo, KRN4884 (1-10 micrograms/kg, intravenously [i.v.]), Ki1769 (10-100 micrograms/kg, i.v.) and Ki3005 (3-30 micrograms/kg, i.v.) produced dose-dependent decreases in mean blood pressure with slight increases in heart rate. At 10 micrograms/kg, i.v., the hypotensive effect of KRN4884 was about the same as that of Ki3005 and about 5-fold more pronounced than that of Ki1769. The hypotensive action remained for a longer period after KRN4884 administration. In rats pre-treated with glibenclamide (20 mg/kg, i.v.), the hypotensive effect of KRN4884 was abolished. These results suggest that the effect of KRN4884 in vitro and in vivo is based on its K channel opening action and that the in vitro vasorelaxant effect of these compounds in aortic rings does not predict their relative hypotensive effect in vivo.

Animals↗

PubMed1996

Effects of the potassium channel openers KRN4884 and levcromakalim on the contraction of rat aorta induced by A23187, compared with nifedipine.

We examined the different vasodilatory effects of the K+ channel openers levcromakalim and 5-amino-N- [2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine (KRN4884), and the Ca2+ channel blocker nifedipine in the rat aorta. KRN 4884 (10(-10)-10(-5) M) and nifedipine (10(-10)-10(-5) M) produced concentration-dependent relaxation in the rat aorta precontracted by 25 mM KCl. The K+ channel blocker glibenclamide (1 microM) inhibited the relaxation induced by KRN4884 but did not influence nifedipine-induced relaxation. KRN4884 had almost no effect on contraction induced by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl. These results indicate that KRN4884 is a K+ channel opener. We investigated the relaxant effects of KRN4884 (10(-10)-10(-5) M), levcromakalim (10(-9)-10(-5) M) and nifedipine (10(-9)-10(-5) M) on A23187 (1 microM)-induced contraction. KRN4884 and levcromakalim had a potent relaxant effect but nifedipine only a weak effect on the smooth muscle contracted by A23187. Glibenclamide (1 microM) inhibited the relaxation induced by KRN4884 and levcromakalim, but did not influence the nifedipine-induced relaxation. KRN4884 (1 microM) produced a larger relaxation of A23187-induced contraction but had little effect on the increase in intracellular [Ca2+] induced by A23187. These results suggest that KRN4884 is a specific K+ channel opener and its vasodilating mechanisms involve not only deactivation of Ca2+ channels but also a decrease in the Ca2+ sensitivity of contractile elements.

Animals↗

PubMed1996

Illusory line motion in visual search: attentional facilitation or apparent motion?

A line, presented instantaneously, is perceived to be drawn from one end when a dot is flashed at that end prior to the presentation of the line. Although this phenomenon, called illusory line motion, has been attributed to accelerated processing at the locus of attention, preattentive (stimulus-driven) motion mechanisms might also contribute to the line-motion sensation. We tested this possibility in an odd-target-search task. The stimulus display consisted of two, four, or eight pairs of dots and lines. All lines were presented on the same side of the dots (eg right), except for the target line, which was presented on the opposite side (left). Subjects were asked to report the presence or absence of the target, which was presented in half of the trials. Low error rates for target detection (about 10%) even when the display consisted of eight dot-line pairs (ie display size was eight) indicated that illusory line motion could be perceived simultaneously at many locations. The interstimulus interval (ISI) between the dots and lines (0-2176 ms) and the contrast polarity (both dots and lines were brighter than the background, or dots were darker and lines were brighter) were also manipulated. When an ISI of a few hundred milliseconds was inserted, target detection was nearly impossible with larger display sizes. When the contrast polarity was changed, the target-detection performance was impaired significantly, even with no ISI. Moreover, it was found that the effects of display size, ISI, and contrast polarity were comparable in searches for a two-dot apparent-motion target. These results support the idea that preattentive, apparent-motion mechanisms, as well as attentional mechanisms, contribute to illusory line motion.

Attention↗

PubMed1996

[The effect of stimulus-driven factor on attentional capture: evidence from visual search paradigm containing static and dynamic stimuli].

The present study investigated the nature of attentional control when the stimulus display contained both static and dynamic items. Subjects searched for a target defined by color presented among nontargets, one of which was a distractor with a unique feature in a different stimulus dimension. Experiment 1 showed that the presence of a distractor with a task irrelevant form hindered identification of the color-defined target. When it was easy to distinguish the target from the other items, this attentional capture was not observed even if the display contained a motion distractor (Experiment 2). Decreasing the saliency of a target color yielded the attentional capture by a motion distractor and interfered target identification performance (Experiment 3). These results suggest that the attentional control mainly depends on the stimulus-driven activations caused by differences between features in stimulus dimensions whether the target and the distractor are defined by static or dynamic features. In order to explain these findings of the attentional capture, a possibility for proposing the single activation map model was discussed.

Adult↗

PubMed1995

Calcium supplementation attenuates an enhanced platelet function in salt-loaded mildly hypertensive patients.

We designed this study to evaluate the effect of low versus high calcium intake on platelet function in salt-loaded patients with mild hypertension. After a 7-day period of dietary salt restriction, 19 patients were placed on a high salt (300 mmol/d), low calcium (6.25 mmol/d) diet for 7 days; 10 of these patients were given 54 mmol/d of supplementary calcium, and 9 patients were given placebo. At the end of the low and high salt regimens, we evaluated changes in blood pressure, platelet aggregation, and the platelet release reaction measured as plasma beta-thromboglobulin and platelet factor 4 levels. With high salt intake, significant increases in mean blood pressure (P < .02), red blood cell sodium (P < .01), and platelet aggregation induced by 3 mumol/L ADP (P < .01) and by 3.0 mg/L epinephrine (P < .05) were observed in the placebo-treated patients but not in the calcium-supplemented ones. Compared with the placebo-treated patients, calcium-supplemented patients had a smaller weight gain (P < .05) but excreted more sodium and calcium (P < .01) at the end of the high salt regimen. Calcium supplementation resulted in decreases in beta-thromboglobulin (P < .05), platelet factor 4 (P < .01), and plasma and urinary excretions of norepinephrine (P < .02) during the high salt, low calcium regimen. The decrease in plasma norepinephrine correlated positively with the decreases in beta-thromboglobulin (r = .72, P < .02) and platelet factor 4 (r = .85, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

[Object-specific priming in apparent motion display].

The perceptual process of an object with multiple features mainly consists of two stages. At first, features are encoded independently at the modular level (feature level). Secondly, they are recombined to build a temporal representation of the object (conjunctive level). Using the apparent motion technique in which stimuli were defined by color and shape, we examined the levels at which the object-specific priming takes place. Although the discrimination of the second stimulus was facilitated when it shared the features with the first stimulus, the priming effects were different according to the number of stimulus items of the first frame. When the first frame contained one stimulus item, the priming benefits were obtained at the both conjunctive and the feature levels. However, the benefit was found only at the feature level when the item number was increased to eight (one of them disappeared in the following frames as the apparent motion stimulus). The roles of modular analysis and attention integration were discussed in terms of the economical validity of feature preservation in object perception.

Adult↗

PubMed1994

Retinoic acid transport to lens epithelium in human aqueous humor.

Retinoids, in particular retinoic acid, are required for the normal growth and maintenance of many types of cells, including epithelial cells. The metabolism of lens epithelial cells, which are exposed to aqueous humor in the anterior chamber, is thought to be dependent upon aqueous humor dynamics. In human eyes undergoing cataract surgery, we measured retinoic acid levels using reverse-phase high performance liquid chromatography to investigate the possible role of aqueous humor in the transport of retinoic acid to lens epithelial cells. The retinoic acid level in the aqueous humor and the lens epithelial cells was 23.3 +/- 2.3 pmol/ml and 1.8 +/- 0.8 pmol/micrograms protein, respectively. Fluorescence spectra study suggested the presence of endogenous retinoid-protein complexes in the aqueous humor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the major protein in aqueous humor was albumin, a natural carrier protein of retinoic acid in the blood. From these results, we conclude that the aqueous humor may supply retinoic acid to the lens epithelial cells in human eyes.

Aged↗

PubMed1993

[The effect of stimulus motion on visual search].

One of the unsettled issues in visual search research is whether the search for a conjunction of motion and the other physical feature (e.g. color or shape) is serial or parallel. In the present experiment, the subjects (six undergraduate students) were instructed to search for a target defined by color, shape, motion, or combinations of the two out of these three features, and the reaction time was measured. The slopes of the regression (number of items in the display vs. reaction time) are the largest for a target defined by a conjunction of color and shape, the smallest for a target defined by one feature, and intermediate for a moving conjunctive target. These results are consistent with those of McLeod and colleagues (1988, 1991) which suggest that a specific visual subsystem operates as a movement filter.

Adult↗

PubMed1992

The structure of glutaraldehyde in aqueous solution determined by ultraviolet absorption and light scattering.

The structure of glutaraldehyde (GA) in aqueous solutions has been the subject of much debate. Since there were fundamental problems in the experiments in the preceding studies, in this article, the structure of GA was investigated with uv absorption and light scattering to avoid those problems. It was discovered that 70% glutaraldehyde solution contains a large quantity of polymeric species with cyclic hemiacetal structure. On dilution, the polymerized glutaraldehyde slowly converted to monomers. In dilute solution, glutaraldehyde is almost monomeric at pH 3-8, the major portion taking the cyclic hemiacetal structure. The structure of GA in 20% solution is similar to that in more dilute solution. alpha, beta-Unsaturated structure does not exist in aqueous solution regardless of the concentration of glutaraldehyde.

Glutaral↗