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Biomedical subjects

M Iino

Publications and source records attributed to M Iino.

At least 109 records · Page 6Linked to original sources
PubMed1996

Impaired calcium regulation of smooth muscle during chronic vasospasm following subarachnoid hemorrhage.

The intracellular calcium level was determined in the canine basilar artery to investigate whether Ca2+ regulation of its smooth muscle is altered during chronic vasospasm following subarachnoid hemorrhage. A double-hemorrhage model was used. The occurrence of vasospasm was confirmed angiographically 7 days after initial hemorrhage. The intracellular calcium concentration ([Ca2+]i) of smooth muscle was measured using Fura-2. Fluorescence to excitation at 340 and 356 nm was monitored and the ration R340/356 was used as the indicator of [Ca2+]i. When the extracellular calcium concentration ([Ca2+]e) was increased from pCa 8 to 2, [Ca2+]i also increased. In the spastic arteries, the [Ca2+]e - [Ca2+]i curve was elevated as compared with the normal arteries. Treatment with ionomycin elevated the curve in the normal group, but it had little effect in the spastic arteries. Values of [Ca2+]i, calculated in multiples of Kd, were greater in the spastic arteries. Diltiazem (10(-5) mol/L) partially suppressed the augmented [Ca2+]i signal in the spastic arteries, whereas it did not affect the curve in the control group. These results indicate that the calcium regulation of smooth muscle is impaired after subarachnoid hemorrhage, which may contribute to the pathogenesis of chronic vasospasm.

Animals↗
PubMed1996

Phytochrome is required for the occurrence of time-dependent phototropism in maize coleoptiles

Time-dependent phototropism (TDP), sometimes called second positive curvature, occurs when the duration of phototropic stimulation with blue light (B) exceeds a few minutes. TDP was characterized in maize (Zea mays L.) coleoptiles raised under continuous red light (R). Subsequently, coleoptiles adapted to darkness were used to investigate the effect of R on TDP. It was found that TDP, which is induced in R-grown coleoptiles, does not occur in dark-adapted coleoptiles and that dark-adapted coleoptiles begin to show TDP after treatment with R. The TDP responsiveness became maximal 1-2 h after treatment with a R pulse and decreased during the next few hours. At least 10 min was required after a short pulse of R before the coleoptile began to respond to B for the induction of TDP. The effect of R in establishing the TDP responsiveness was totally suppressed by a pulse of far-red light given immediately after an inductive pulse of R. It is concluded that the mechanism of TDP requires for its establishment a R signal perceived by phytochrome. The TDP of R-grown and R-pretreated coleoptiles showed relationships to stimulation times and fluence rates that are similar to those reported for oat coleoptiles, except that TDP of maize showed a sharp increase in its magnitude within a narrow range of stimulation times as short as 5-10 min.

Cotyledon↗
PubMed1996

Gravitropism of maize and rice coleoptiles: dependence on the stimulation angle.

Gravitropism of maize and rice coleoptiles was investigated with respect to its dependence on the angle of displacement or the initial stimulation angle (ISA). Close examination of curvature kinetics and the response to a drop in stimulation angle (SA) indicated that the gravtropic response during an early but substantial part of the curvature development is directly related to the ISA, there being no effect of the reduction of SA resulting from the curvature response itself. On the basis of this finding, the relationship between the steady SA and the curvature rate was determined. In maize, the curvature rate increased linearly with the sines of SAs up to an SA of 90 degrees. Rice coleoptiles, however, showed a saturation curve in the same range of SAs. The saturation profile was nearly identical between coleoptiles grown in air and those submerged in water, although the latter elongated much faster. Rice coleoptiles appeared to be far more sensitive to gravity than maize coleoptiles. It is concluded that the sensitivity to gravity, assessed through dependence on ISA, is a property inherent to a given gravitropic organ. Long-term measurements of curvature indicated that the coleoptiles bend back past the vertical. This overshooting was marked in submerged rice coleoptiles.

Air↗
PubMed1996

Effect of calmodulin antagonists on calmodulin-induced biphasic modulation of Ca(2+)-induced Ca2+ release.

1. Calmodulin (CaM) has a biphasic effect on Ca(2+)-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR): potentiation and inhibition at low (pCa > 6.0) and high (pCa 5) Ca2+ concentrations, respectively. To characterize the mode of action of CaM, we studied the effect of CaM antagonists on the CICR in skinned muscle fibres of the rabbit. Ca2+ release was measured by microfluorometry with Fura-2. 2. A CaM antagonist, trifluoperazine (TFP), potentiated the CICR in a dose-dependent manner (10-300 microM) at pCa 6, where a simple reversal of the CaM effect would be inhibition of the CICR. Furthermore, 100 microM TFP sensitized the CICR to Ca2+. A similar effect was produced by other CaM antagonists that were tested: chlorpromazine, W-7, mastoparan, and peptide fragment of CaM-binding residues of CaM-dependent protein kinase II. 3. The biphasic effect of CaM on the CICR was observed even in the presence of high concentrations of CaM antagonists or CaM-bindings peptides. 4. From these results we suggest that CaM has a unique mode of action on the CICR which is quite different from the effect of CaM on known enzymes.

Animals↗
PubMed1996

[Recent progress of diagnostic imaging for aortic dissection].

After advent newly developed imaging modalities, diagnosis for aortic dissection had been extremely easier as compared with at the time when we had diagnosed this lesion solely by angiography. Characteristics of intra-arterial digital subtraction angiography (DSA), computed tomography (CT), magnetic resonance imaging (MRI) and transesophageal echocardiography (TEE) for this lesion was reviewed. In particular, we described how much three dimensional reconstructed CT using ultrafast computed tomography (electron beam tomography: EBT) and helical computed tomography (HCT) contribute to diagnosis for this disease. Furthermore, it was commented upon how to diagnose for acute aortic dissection with modern diagnostic tools based on our praxis.

Aortic Dissection↗
PubMed1996

Substrate recognition mechanism of human beta-adrenergic receptor kinase 1 based on a three-dimensional model structure.

Although its detailed substrate specificity is not precisely known, beta-adrenergic receptor kinase 1 phosphorylates beta 2-adrenergic receptors and other G protein-coupled receptors. To elucidate the ligand recognition mechanism of the enzyme and the consensus sequence required for substrates, a three-dimensional structure of the catalytic domain of the enzyme was modeled based on the X-ray crystal structure of the catalytic subunit of cyclic AMP-dependent protein kinase A. When the phosphorylation residue of the substrate was defined as the p position in the model of beta-adrenergic receptor kinase 1, the present study suggested that the consensus sequence recognized by this enzyme would consist of a basic residue at p-3 and an acidic residue at p-2.

Amino Acid Sequence↗
PubMed1995

Spermine mediates inward rectification of Ca(2+)-permeable AMPA receptor channels.

AMPA-gated glutamate receptors with an inwardly rectifying current-voltage (I-V) relationship and substantial Ca2+ permeability are expressed in a population of cultured rat hippocampal neurones (type II neurones). The inward rectification of these AMPA receptors was gradually lost in cell-free membrane patches. The I-V relationship of the AMPA receptors displayed a slight outward rectification in most patches 10 min after excision. This loss of inward rectification was not accompanied by a change in the Ca2+ permeability. The inward rectification was maintained by applying physiological concentrations of spermine to the cytoplasmic side of patch membranes. These results indicate that some cytoplasmic factor mediates inward rectification in the Ca(2+)-permeable AMPA receptors, and that a candidate for this substance is spermine.

Animals↗
PubMed1995

Enhancing effect of calmodulin on Ca(2+)-induced Ca2+ release in the sarcoplasmic reticulum of rabbit skeletal muscle fibres.

1. We analysed the effect of calmodulin on Ca(2+)-induced Ca2+ release (CICR) in the sarcoplasmic reticulum (SR) using chemically skinned fibres of rabbit psoas muscle. Ca2+ release was measured using fura-2 microfluorometry. 2. In saponin-skinned fibres, calmodulin potentiated Ca2+ release at low Ca2+ concentrations (< 3 microM), while it showed an inhibitory effect at high Ca2+ concentrations (3-30 microM). 3. Co-application of ryanodine and calmodulin at 0.3 microM Ca2+, but not ryanodine alone, induced a decline in the Ca2+ uptake capacity of the SR, an effect expected from the open-lock of active CICR channels by ryanodine. Thus, potentiation of Ca2+ release by calmodulin at low Ca2+ concentrations can be regarded as a result of the activation of the ryanodine receptor. 4. Greater concentrations of calmodulin were required for potentiation of CICR at low Ca2+ concentrations (1 microM) than for inhibition at high Ca2+ concentrations (10 microM). 5. In beta-escin-permeabilized fibres in which intrinsic calmodulin was retained, the rates of CICR were similar to those measured in the presence of 1 microM calmodulin in saponin-permeabilized fibres. 6. These results suggest that calmodulin plays an important role in the regulation of CICR channels in intact skeletal muscle fibres.

Animals↗
PubMed1995

Characterization of the binding of factor Xa to fibrinogen/fibrin derivatives and localization of the factor Xa binding site on fibrinogen.

The binding of human factor Xa to fibrinogen and its derivatives was characterized. Factor Xa bound to immobilized fibrin with a concentration at half-maximal binding (C50) of 100 nM. The 4-carboxyglutamic acid (Gla) domain of factor Xa is important in factor Xa binding to fibrin monomer, based on the following observations; the binding requires Ca2+; Gla-domain-lacking factor Xa could not bind to fibrin; factor Xa binding was significantly reduced by prior treatment of factor Xa with factor IX/factor-X-binding protein from the venom of Trimeresurus flavoviridis which specifically binds to the Gla domain of human factors IX and X. Factor Xa also bound to fibrinogen, fibrinogen degradation products (FDP)-D and FDP-E, with a similar affinity (C50 = 75-131 nM). In a solution-phase equilibrated binding assay, approximately 0.76 mol factor Xa bound to 1 mol fibrinogen with a dissociation constant of 180 nM. The binding of 125I-labeled factor Xa to the fibrin monomer was inhibited markedly by unlabeled factor Xa, but only slightly by thrombin, suggesting that the binding site of factor Xa on fibrin monomer differs from that of thrombin. We localized the binding site of factor Xa on fibrinogen: factor Xa bound strongly to the A alpha chain, but weakly to the B beta and gamma chains of fibrinogen. The A alpha chain was then digested with lysyl endopeptidase and separated by reverse-phase HPLC. Among resulting peptides, factor Xa bound specifically to a peptide corresponding to residues Asp82-Lys123 of the A alpha chain. This factor-Xa-binding site is located in the boundary between the central E domain and the terminal D domain of fibrinogen and is apparently distinct from the reported thrombin-binding site.

Binding Sites↗
PubMed1995

Stretch-induced enhancement of contractions in uterine smooth muscle of rats.

1. We studied the effect of servo-controlled stretch of smooth muscle strips from rat uterus on tension and intracellular Ca2+ concentration ([Ca2+]i, using fura-2 as an indicator) at 30 degrees C. 2. When quiescent uterine muscle strips were stretched at a ramp time of 0.5 s by multiples of 5% of the resting muscle length (L0) up to 40%, forty-two out of sixty muscle strips responded with a transient active contraction and a [Ca2+]i increase. The minimum excursion of stretch required for contraction was 26.3 +/- 7.5% of L0 (mean +/- S.D.). The peak response had an all-or-none property and was almost independent of the duration of stretch. 3. Stretches of 30 or 35% of L0 induced contraction in most cases when rapidly applied in 0.2-0.5 s, but slowly applied stretch (ramp duration of 5-10 s) rarely induced contraction. 4. The stretch-induced response was inhibited by the removal of extracellular Ca2+ or by the addition of 10 nM nicardipine. However, it was unaffected by 1 microM tetrodotoxin, 1 microM atropine or by 10 microM cyclopiazonic acid, an inhibitor of Ca2+-ATPase in intracellular Ca2+ stores. 5. When a stretch of 15-35% of L0 was applied during the relaxation phase of 10 nM oxytocin-induced rhythmic contractions, the first contraction after the stretch occurred earlier than that expected from the control rhythm. However, the frequency of the subsequent rhythm returned to almost the control level even during continued application of stretch, although the half-width of rhythmic contractions was increased during stretch. 6. The present study demonstrates that stretch of uterine muscle induces a transient contraction due to Ca2+ influx, which is myogenic and dependent on the excursion and velocity of stretch. The all-or-none property of the stretch-induced contractions suggests initiation of Ca2+ spikes. Furthermore, stretch modulates the oxytocin-induced rhythmic contractions.

Animals↗
PubMed1995

Ca(2+)-induced Ca2+ release in myocytes from dyspedic mice lacking the type-1 ryanodine receptor.

While subtypes 1 and 2 of the ryanodine receptor (RyR) function as intracellular Ca2+ release channels, little is known about the function of the third subtype (RyR-3), first identified in brain. Myocytes from mice homozygous for a targeted mutation in the RyR-1 gene (dyspedic mice) can now be used for a study on the function of RyR-3, which is predominantly expressed in these cells according to our reverse transcription-polymerase chain reaction analysis. We here demonstrate in these myocytes caffeine-, ryanodine- and adenine nucleotide-sensitive Ca(2+)-induced Ca2+ release with approximately 10 times lower sensitivity to Ca2+ than that of RyR-1. Although RyR-3 does not mediate excitation-contraction coupling of the skeletal muscle type, we propose that RyR-3 may induce intracellular Ca2+ release in response to a Ca2+ rise with a high threshold.

Adenine Nucleotides↗
PubMed1995

Identification of the oligosaccharide structures of human coagulation factor X activation peptide at each glycosylation site.

Human blood coagulation factor X has two N-linked oligosaccharides at Asn39 and Asn49 residues and two O-linked oligosaccharides at Thr17 and Thr29 residues in the region of the factor X activation peptide (XAP) which is cleaved off during its activation by factor IXa. We determined the structure of oligosaccharides in the XAP region of human factor X. Four glycopeptides each containing a glycosylation site were isolated by digestion of XAP with endoproteinase Asp-N followed by reversed-phase HPLC. N-linked oligosaccharides released from the glycopeptides by glycoamidase A digestion were derivatized with 2-aminopyridine. Pyridylamino(PA)-oligosaccharides were separated by HPLC into neutral and sialyl oligosaccharides using an anion-exchange column. Structures of oligosaccharides and their contents at each glycosylation site were determined by a two-dimensional sugar mapping method. The contents of the neutral oligosaccharides at Asn39 and Asn49 residues were 32.5% and 30.0%, respectively. Six neutral and twelve monosialyl oligosaccharides isolated from both N-linked glycosylation sites showed similar elution profiles composed of bi-, tri- and tetra-antennary complex type oligosaccharides. The predominant component in neutral oligosaccharides was biantennary without a fucose residue. Two major monosialyl oligosaccharides were also biantennary without fucose and with a Neu5Ac alpha 2-->6 residue. In addition, the structures of O-linked oligosaccharides at Thr17 and Thr29 residues were suggested to be disialylated Gal beta 3GalNAc sequences by their component analyses.

Asparagine↗
PubMed1994

Visualization of neural control of intracellular Ca2+ concentration in single vascular smooth muscle cells in situ.

The intermittent rise in intracellular Ca2+ concentration ([Ca2+]i oscillation) has been observed in many types of isolated cells, yet it has not been demonstrated whether it plays an essential role during nerve stimulation in situ. We used confocal microscopy to study Ca2+ transients in individual smooth muscle cells in situ within the wall of small arteries stimulated with perivascular sympathetic nerves or noradrenaline. We show here that the sympathetic adrenergic regulation of arterial smooth muscle cells involves the oscillation of [Ca2+]i that propagates within the cell in the form of a wave. Ca2+ release from intracellular stores plays a key role in the oscillation because it is blocked after the store depletion by ryanodine treatment. Ca2+ influx through the plasma membrane sustains the oscillation by replenishing the Ca2+ stores. These results demonstrate the involvement of [Ca2+]i oscillations in the neural regulation of effector cells within the integrated system.

Animals↗
PubMed1994

Dynamic properties of bound water studied through macroscopic water relaxations in concentrated protein solutions.

Magnetization transfer experiments using an off-resonance irradiation technique were performed on bovine serum albumin solutions by varying the irradiation frequency and concentration. Observed macroscopic magnetizations of water protons were well expressed by the rate equations of populations for spins, which gave the tumbling time of protein protons and the intrinsic relaxation rates of water and protein protons. These parameters conformed to a model of rapid-exchange water system with bound water molecules in the interior of the protein that interact with protein protons. Analysis of the data enabled the separation of relaxation rates into the respective contributions by the interior bound water and water in the hydration layer at the protein surface, and determined the amounts and the average correlation times of these water fractions. The average residence time of the interior bound water with respect to exchange with the bulk water was found to be (5 +/- 2).10(-6) s. The estimation of the hydration layer showed excellent agreement with the amount measured by a thermodynamical method.

Magnetic Resonance Spectroscopy↗