Biomedical subjects

J Saito

Publications and source records attributed to J Saito.

At least 19 recordsLinked to original sources

PubMed2003

Different spatial processing for stimulus-centered and body-centered representations.

The authors describe a patient who experienced two successive strokes in the right hemisphere. After the first stroke, she showed stimulus-centered left neglect confined to right space on a circle discrimination task, which resolved. After the second stroke, she showed body-centered left neglect on the same task. These observations of two types of left neglect in the same patient suggest there are at least two distinct spatial attentional systems in the brain: global and focal attentional systems.

Aged↗

PubMed2003

Emergency endovascular stent-grafting for infected pseudoaneurysm of brachial artery.

The use of covered stents in an infected field is controversial. It is generally recommended that infected aneurysms be treated using autografts or allografts. We report a case of infected brachial pseudoaneurysms that developed after medical debridement of a methicillin-resistant Staphylococcus aureus (MRSA)-infected wound of the right arm and emergency brachial artery bypass-grafting using the saphenous vein, which was successfully treated by endovascular stent-grafting followed by antibiotic administration. The present case suggests that endovascular stent-grafting prevents rupture and occlusion of infected aneurysms and enables the continued administration of antibiotics.

Adult↗

PubMed2001

The core of the motor domain determines the direction of myosin movement.

Myosins constitute a superfamily of at least 18 known classes of molecular motors that move along actin filaments. Myosins move towards the plus end of F-actin filaments; however, it was shown recently that a certain class of myosin, class VI myosin, moves towards the opposite end of F-actin, that is, in the minus direction. As there is a large, unique insertion in the myosin VI head domain between the motor domain and the light-chain-binding domain (the lever arm), it was thought that this insertion alters the angle of the lever-arm switch movement, thereby changing the direction of motility. Here we determine the direction of motility of chimaeric myosins that comprise the motor domain and the lever-arm domain (containing an insert) from myosins that have movement in the opposite direction. The results show that the motor core domain, but neither the large insert nor the converter domain, determines the direction of myosin motility.

Animals↗

PubMed2001

Dual regulation of mammalian myosin VI motor function.

Myosin VI is expressed in a variety of cell types and is thought to play a role in membrane trafficking and endocytosis, yet its motor function and regulation are not understood. The present study clarified mammalian myosin VI motor function and regulation at a molecular level. Myosin VI ATPase activity was highly activated by actin with K(actin) of 9 microm. A predominant amount of myosin VI bound to actin in the presence of ATP unlike conventional myosins. K(ATP) was much higher than those of other known myosins, suggesting that myosin VI has a weak affinity or slow binding for ATP. On the other hand, ADP markedly inhibited the actin-activated ATPase activity, suggesting a high affinity for ADP. These results suggested that myosin VI is predominantly in a strong actin binding state during the ATPase cycle. p21-activated kinase 3 phosphorylated myosin VI, and the site was identified as Thr(406). The phosphorylation of myosin VI significantly facilitated the actin-translocating activity of myosin VI. On the other hand, Ca(2+) diminished the actin-translocating activity of myosin VI although the actin-activated ATPase activity was not affected by Ca(2+). Calmodulin was not dissociated from the heavy chain at high Ca(2+), suggesting that a conformational change of calmodulin upon Ca(2+) binding, but not its physical dissociation, determines the inhibition of the motility activity. The present results revealed the dual regulation of myosin VI by phosphorylation and Ca(2+) binding to calmodulin light chain.

Actin Cytoskeleton↗

PubMed2001

Overexpression and overactivation of Akt in thyroid carcinoma.

Enhanced activation of Akt occurs in Cowden's disease, an inherited syndrome of follicular thyroid, breast, colon, and skin tumors, via inactivation of its regulatory protein, PTEN. Whereas PTEN inactivation is uncommon in sporadic thyroid cancer, activation of growth factor pathways that signal through Akt is frequently identified. We hypothesized that Akt overactivation could be a common finding in sporadic thyroid cancer and might be important in thyroid cancer biology. We examined thyroid cancer cells lines and benign and malignant thyroid tissue for total Akt activation and isoform-specific Akt expression. In thyroid cancer cells, Akt 1, 2, and 3 proteins were expressed, total Akt was activated by insulin phosphatidylinositol 3'-kinase, and inhibition of phosphatidylinositol 3'-kinase reduced cell viability. In human thyroid tissue, increased levels of phosphorylated total Akt were identified in follicular but not papillary cancers compared with normal tissue. Levels of Akt 1 and 2 proteins and Akt 2 RNA were elevated only in the follicular cancers. In paired samples, Akt 1, 2, 3, and phospho-Akt levels were higher in five of six cancers, including three of three follicular cancers. These data suggest that Akt activation may play a role in the pathogenesis or progression of sporadic thyroid cancer.

Adenocarcinoma, Follicular↗

PubMed2001

Motor function and regulation of myosin X.

Myosin X is a member of the diverse myosin superfamily that is ubiquitously expressed in various mammalian tissues. Although its association with actin in cells has been shown, little is known about its biochemical and mechanoenzymatic function at the molecular level. We expressed bovine myosin X containing the entire head, neck, and coiled-coil domain and purified bovine myosin X in Sf9 cells. The Mg(2+)-ATPase activity of myosin X was significantly activated by actin with low K(ATP). The actin-activated ATPase activity was reduced at Ca(2+) concentrations above pCa 5 in which 1 mol of calmodulin light chain dissociates from the heavy chain. Myosin X translocates F-actin filaments with the velocity of 0.3 microm/s with the direction toward the barbed end. The actin translocating activity was inhibited at concentrations of Ca(2+) at pCa 6 in which no calmodulin dissociation takes place, suggesting that the calmodulin dissociation is not required for the inhibition of the motility. Unlike class V myosin, which shows a high affinity for F-actin in the presence of ATP, the K(actin) of the myosin X ATPase was much higher than that of myosin V. Consistently nearly all actin dissociated from myosin X in the presence of ATP. ADP did not significantly inhibit the actin-activated ATPase activity of myosin X, suggesting that the ADP release step is not rate-limiting. These results suggest that myosin X is a nonprocessive motor. Consistently myosin X failed to support the actin translocation at low density in an in vitro motility assay where myosin V, a processive motor, supports the actin filament movement.

Actins↗

PubMed2001

The tip of the coiled-coil rod determines the filament formation of smooth muscle and nonmuscle myosin.

Myosin II self-assembles to form thick filaments that are attributed to its long coiled-coil tail domain. The present study has determined a region critical for filament formation of vertebrate smooth muscle and nonmuscle myosin II. A monoclonal antibody recognizing the 28 residues from the C-terminal end of the coiled-coil domain of smooth muscle myosin II completely inhibited filament formation, whereas other antibodies recognizing other parts of the coiled-coil did not. To determine the importance of this region in the filament assembly in vivo, green fluorescent protein (GFP)-tagged smooth muscle myosin was expressed in COS-7 cells, and the filamentous localization of the GFP signal was monitored by fluorescence microscopy. Wild type GFP-tagged smooth muscle myosin colocalized with F-actin during interphase and was also recruited into the contractile ring during cytokinesis. Myosin with the nonhelical tail piece deleted showed similar behavior, whereas deletion of the 28 residues at the C-terminal end of the coiled-coil domain abolished this localization. Deletion of the corresponding region of GFP-tagged nonmuscle myosin IIA also abolished this localization. We conclude that the C-terminal end of the coiled-coil domain, but not the nonhelical tail piece, of myosin II is critical for myosin filament formation both in vitro and in vivo.

Actins↗

PubMed2001

Covered stent for renal artery aneurysm.

This is a case of a 51-year-old female with difficult-to-control hypertension and a 3-cm renal artery aneurysm. Successful exclusion of this was performed using a prefabricated stent graft. To our knowledge, this is the first report on the use of a prefabricated covered stent for this indication.

Aneurysm↗

PubMed2001

Autoimmune neutropenia in pregnant women causing neonatal neutropenia.

Autoimmune neutropenia (AIN) can occur during pregnancy. However, neonatal neutropenia occurring in an infant born to a mother with AIN has only rarely been documented. Recently, we have experienced two cases of AIN during pregnancy, both of which caused severe yet transient neonatal neutropenia (< 0.3 x 10(9)/l), probably as a result of transplacental maternal anti-neutrophil autoantibodies. The anti-neutrophil antibodies seemed to be against antigens other than NA1/NA2 because the autoantibodies did not bind to neutrophils of specific NA types selectively in the granulocyte indirect immunofluorescence test. Although AIN is a relatively uncommon disease, neonatal neutropenia caused by maternal AIN may not be quite as rare.

Adult↗

PubMed2001

Effect of procainamide on the postrepolarization refractoriness in cardiac muscle: evaluation using the block coupling interval in the artificial isthmus model in the canine right atrium.

The post-repolarization refractoriness (PRR) is an important factor to determine the conduction block in cardiac muscle. Recently, we proposed the block coupling interval (BCI) as an useful electrophysiological index for evaluating the PRR. In the present study, the effect of procainamide on PRR was evaluated using the BCI and the effective refractory period (ERP). In five beagle dogs, radiofrequency linear ablation was performed on the right atrial surface parallel to the AV groove, forming an artificial isthmus (8-10 mm width and 15-20 mm length). Bipolar recordings were performed in the isthmus at a resolution of 1.2 mm and single extrastimuli with eight basic drive trains were delivered to cause conduction blocks in the isthmus. When a conduction block occurred, the recorded coupling interval at the recording site just proximal to the site of block was defined as BCI. At the site of the block, the ERP and duration of the monophasic action potential (MAP) at each drive cycle length was measured. The PRR was calculated using two different formulas: (1) [ERP-MAP] and (2) [BCI-MAP]. Procainamide was administrated intravenously at a dose of 15 mg/kg after the control study and the whole study protocol was repeated. The site of the block in an individual dog was always the same. BCI, ERP, and MAP were all shortened in accordance with the shortening of the basic drive cycle length, and the BCI was always the longest, ERP the middle, and the MAP was the shortest. The administration of procainamide prolonged each parameter, but the order of BCI > ERP > MAP remained unchanged. The PRR calculated as [BCI-MAP] was prolonged from 15 +/- 10 ms to 29 +/- 8 ms by the administration of procainamide (P = 0.048), but [ERP-MAP] was unchanged (8 +/- 10 ms vs 8 +/- 4 ms). In the conduction block model in the canine right atrium, procainamide prolonged the [BCI-MAP], but did not change the [ERP-MAP]. The procainamide effect of prolonging the PRR might be expressed better by the change in the BCI than the ERP.

Animals↗

PubMed2001

Regulation of FRTL-5 thyroid cell growth by phosphatidylinositol (OH) 3 kinase-dependent Akt-mediated signaling.

Thyrotropin (TSH)-initiated cell cycle progression from G1 to S phase in FRTL-5 thyroid cells requires serum, insulin, or insulin-like growth factor 1 (IGF-1) and involves activation of 3-hydroxy-3-methylglutaryl-CoA reductase, geranylgeranylation of RhoA, p27Kip1 degradation, and activation of cyclin-dependent kinase (cdk) 2. In the present report, we show that the serine-threonine kinase Akt is an important mediator of insulin/IGF-1/serum effects on cell cycle progression in FRTL-5 thyroid cells. The phosphoinositol (OH) 3 kinase inhibitors, Wortmannin (WM) and Ly294002 (LY), block the ability of insulin/IGF-1 to reduce p27 expression, to induce expression of cyclins E, D1, and A as well as cdk 2 and 4, and to phosphorylate retinoblastoma protein. They also inhibit insulin/IGF-1-increased DNA synthesis and cell cycle entrance (S+G2/M). Insulin/IGF-1 rapidly induced activation of Aktl in a PI3 kinase-dependent manner, and increased Aktl RNA levels. Most importantly, FRTL-5 cells transfected with a constitutively active form of Aktl have higher basal rates of DNA synthesis and no longer require exogenous insulin/IGF-1 or serum for TSH-induced growth. In sum, Aktl appears to have an important role in insulin/IGF-1 regulation of FRTL-5 thyroid cell growth and cell cycle progression.

Animals↗

PubMed2001

Usefulness of magnetic resonance imaging for surgical management of extravasation of an antitumor agent: a case report.

We report a case of extravasation of an antitumor agent by preoperative magnetic resonance (MR) imaging. MR studies demonstrated a decreased signal intensity on T1- and T2-weighted images and a strong enhancement of contrast media in injured tissue, including subcutaneous adipose tissue and deep fascia, which was cicatrical macroscopically. The MR findings were in good agreement with the macroscopic findings. We believe that MR imaging is useful for estimating deep tissue damage due to extravasation of an antitumor agent.

Adipose Tissue↗

PubMed2001

Interleukin 1 upregulates ovarian prostaglandin endoperoxide synthase-2 expression: evidence for prostaglandin-dependent/ceramide-independent transcriptional stimulation and for message stabilization.

We have recently documented a marked dependence of ovarian prostaglandin endoperoxide synthase (PGS)-2 transcripts, proteins, and activity on interleukin (IL) 1, a putative intermediary in the ovulatory cascade. The purpose of the present study was to characterize the cellular and molecular mechanisms underlying the ability of IL-1beta to upregulate the steady-state levels of ovarian transcripts corresponding to PGS-2. Results of studies designed to enrich or deplete nitric oxide strongly suggest that the stimulatory effect of IL-1beta on ovarian PGS-2 expression is independent of nitric oxide. Utilization of a series of agents designed to simulate or enhance transduction via the sphingomyelin ceramide cycle suggests that the long-term stimulatory effect of IL-1beta on ovarian PGS-2 gene expression is independent of ceramide. In contrast, inhibition of prostaglandin biosynthesis with a series of distinct inhibitors suggests that the ability of IL-1beta to upregulate ovarian PGS-2 transcripts is due, if only in part, to the generation of endogenous prostaglandin estradiol-17beta (E(2)). Inhibition of protein biosynthesis suggested that the IL-1beta-induced PGS-2 gene expression required de novo protein biosynthesis. Our findings revealed substantial IL-1beta-mediated stabilization of PGS-2 transcripts, as assessed by a threefold increase in the half-life of the message. We have also observed the ability of IL-1beta to upregulate the transcription of PGS-2 promoter constructs subjected to transient transfection into whole-ovarian dispersates (twofold increase as assessed by activation of the luciferase reporter gene). Taken together, these findings suggest that the stimulatory effect of IL-1beta on PGS-2 expression is 1) independent of nitric oxide as well as ceramide, 2) dependent on prostaglandin E(2), 3) contingent on de novo protein biosynthesis, and 4) accounted for by both increased transcription and message stabilization. These observations provide indirect support for the hypothesis that IL-1beta, acting in part through PGS-2 (an obligatory ovulatory principal), may constitute a key intermediary in the ovulatory cascade.

Animals↗

PubMed2001

Post-resuscitative hypothermic bypass reduces ischemic brain injury in swine.

OBJECTIVES: Increasing human and laboratory evidence suggests that post-resuscitative brain hypothermia reduces the pathologic consequences of brain ischemia. Using a swine model of prolonged cardiac arrest, this investigation sought to determine whether unilateral hypothermic carotid bypass was capable of inducing selective brain hypothermia and reducing neurohistologic damage. METHODS: Ventricular fibrillation was induced in common swine (n = 12). After 20 minutes of cardiopulmonary arrest (without ventilatory support or cardiopulmonary resuscitation), systemic extracorporeal bypass was instituted to restore coronary and cerebral perfusion, followed by restoration of normal sinus rhythm. Animals randomized to the normal brain temperature (NBT) cohort received mechanical ventilation and intravenous fluids for 24 hours. The selective brain hypothermia (SBH) cohort received 12 hours of femoral/carotid bypass at 32 degrees C. The bypass temperature was then increased one degree per hour until reaching 37 degrees C and continued at this temperature until completion of the protocol (24 hours). Histopathologic damage was evaluated in two areas of the hippocampus. RESULTS: Normal sinus rhythm was restored in all animals after the systemic (femoral/femoral) bypass was initiated. Nasal temperature (surrogate measure of brain temperature) remained higher than 37.0 degrees C throughout the 24-hour recovery period in the NBT animals. In the SBH cohort, right nasal temperature dropped to the mild hypothermic range (<34 degrees C) two hours after institution of femoral/carotid bypass. This was maintained throughout the 12-hour cooling period without hemodynamic compromise. There was a significant improvement in the neurohistology scores in the CA1 region of the hippocampus of the SBH treated animals as compared with those of the NBT cohort. CONCLUSIONS: Post-resuscitative selective brain hypothermia reduced regional ischemic brain damage in swine with prolonged ventricular fibrillation.

Animals↗

PubMed2001

Rapid development of brain hypothermia using femoral-carotid bypass.

OBJECTIVES: Advances in the field of cardiopulmonary resuscitation have led to an increasing number of patients initially surviving sudden cardiac arrest. Unfortunately, most of these patients do not recover from the resultant anoxic brain insult. Several animal and human trials have suggested that post-resuscitative brain hypothermia may improve neurologic recovery after cardiopulmonary arrest. Present cooling methods are slow, induce only brain surface cooling, or result in systemic hypothermia. The authors tested the hypothesis that unilateral hypothermic carotid bypass would induce bilateral brain cooling without evoking systemic hypothermia or hemodynamic instability. METHODS: Anesthetized, ventilated common swine (n = 6, 24-37 kg) underwent right femoral and carotid artery bypass cannulation. Central and peripheral hemodynamic parameters were recorded every 2 minutes throughout the procedure. Thermodynamic parameters included bilateral frontal lobe, bilateral nasopharyngeal, pulmonary artery, and rectal temperatures. Hypothermic femoral-carotid bypass was accomplished by drawing blood from the right femoral artery, cooling it to 24 degrees C, and returning it to the right carotid artery at a flow rate of 5 mL/kg/min for 30 minutes. RESULTS: With initiation of cooling, brain temperatures dropped rapidly from baseline of 37.2 degrees C to 30.6 degrees C (right frontal lobe) and 33.1 degrees C (left frontal lobe) at 30 minutes. Pulmonary artery and rectal temperatures also decreased, but never reached mild hypothermic levels (34 degrees C). There was no significant change in any hemodynamic parameters during brain cooling. CONCLUSIONS: Femoral-carotid hypothermic bypass rapidly induced a state of selective brain hypothermia without causing systemic hypothermia or hemodynamic instability.

Analysis of Variance↗

PubMed2001

Evaluation of post-repolarization refractoriness for conduction block in cardiac muscle: studies in an artificial isthmus in the canine right atrium.

Post-repolarization refractoriness (PRR) is an important factor in determining conduction block and is the difference between the effective refractory period (ERP) and the duration of the monophasic action potential (MAPD). In the present study, conduction block in an artificial isthmus in the canine atrium was evaluated and the coupling interval of a premature beat, which caused the block, was defined as the block coupling interval (BCI). The usefulness of this value was also evaluated. Radiofrequency linear ablation was performed on the right atrial surface parallel to the atrioventricular groove in 5 mongrel dogs, and an artificial isthmus (8-10mm wide and 25-30mm long) was created. Fourteen simultaneous unipolar recordings were performed in the isthmus with a resolution of 1.2 mm. Single extra-stimuli with basic drive train were delivered to induce conduction block in the isthmus and when it occurred, the coupling interval at the recording site just proximal to the site of the block was defined as the BCI. At the site of the block, the ERP and MAPD at each drive cycle length were measured. The PRR was calculated using 2 different formulae: (1) [ERP-MAPD], and (2) [BCI-MAPD]. It was found that each value was shortened in accordance with the shortening of the basic drive cycle length. In all basic drive trains, BCI>ERP>MAPD, and [ERP-MAPD] was always shorter than [BCI-MAPD]. In the shorter cycle length of basic drives, the difference between [ERP-MAPD] and [BCI-MAPD] was more prominent. In the artificial isthmus model in the canine atrium, BCI was always longer than the ERP measured at the same site as the block. Because the ERP may not directly reflect the block phenomenon, the electrophysiologic evaluation should use the BCI instead, as in the PRR evaluation.

Action Potentials↗

PubMed2000

Ca(2+)-dependent regulation of the motor activity of myosin V.

Mouse myosin V constructs were produced that consisted of the myosin motor domain plus either one IQ motif (M5IQ1), two IQ motifs (M5IQ2), a complete set of six IQ motifs (SHM5), or the complete IQ motifs plus the coiled-coil domain (thus permitting formation of a double-headed structure, DHM5) and expressed in Sf9 cells. The actin-activated ATPase activity of all constructs except M5IQ1 was inhibited above pCa 5, but this inhibition was completely reversed by addition of exogenous calmodulin. At the same Ca(2+) concentration, 2 mol of calmodulin from SHM5 and DHM5 or 1 mol of calmodulin from M5IQ2 were dissociated, suggesting that the inhibition of the ATPase activity is due to dissociation of calmodulin from the heavy chain. However, the motility activity of DHM5 and M5IQ2 was completely inhibited at pCa 6, where no dissociation of calmodulin was detected. Inhibition of the motility activity was not reversed by the addition of exogenous calmodulin. These results indicate that inhibition of the motility is due to conformational changes of calmodulin upon the Ca(2+) binding to the high affinity site but is not due to dissociation of calmodulin from the heavy chain.

Actins↗

PubMed2000

Two classes of androgen receptor elements mediate cooperativity through allosteric interactions.

Genes uniquely regulated by the androgen receptor (AR) typically contain multiple androgen response elements (AREs) that in isolation are of low DNA binding affinity and transcriptional activity. However, specific combinations of AREs in their native promoter context result in highly cooperative DNA binding by AR and high levels of transcriptional activation. We demonstrate that the natural androgen-regulated promoters of prostate specific antigen and probasin contain two classes of AREs dictated by their primary nucleotide sequence that function to mediate cooperativity. Class I AR-binding sites display conventional guanine contacts. Class II AR-binding sites have distinctive atypical sequence features and, upon binding to AR, the DNA structure is dramatically altered through allosteric interactions with the receptor. Class II sites stabilize AR binding to adjacent class I sites and result in synergistic transcriptional activity and increased hormone sensitivity. We have determined that the specific nucleotide variation within the AR binding sites dictate differential functions to the receptor. We have identified the role of individual nucleotides within class II sites and predicted consensus sequences for class I and II sites. Our data suggest that this may be a universal mechanism by which AR achieved unique regulation of target genes through complex allosteric interactions dictated by primary binding sequences.

Allosteric Regulation↗