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M Iino

Publications and source records attributed to M Iino.

At least 19 recordsLinked to original sources
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

Excitation-contraction uncoupling and muscular degeneration in mice lacking functional skeletal muscle ryanodine-receptor gene.

Contraction of skeletal muscle is triggered by the release of Ca2+ from the sarcoplasmic reticulum (SR) after depolarization of transverse tubules. The ryanodine receptor exists as a 'foot' protein in the junctional gap between the sarcoplasmic reticulum and the transverse tubule in skeletal muscle, and is proposed to function as a calcium-release channel during excitation-contraction (E-C) coupling. Previous complementary DNA-cloning studies have defined three distinct subtypes of the ryanodine receptor in mammalian tissues, namely skeletal muscle, cardiac and brain types. We report here mice with a targeted mutation in the skeletal muscle ryanodine receptor gene. Mice homozygous for the mutation die perinatally with gross abnormalities of the skeletal muscle. The contractile response to electrical stimulation under physiological conditions is totally abolished in the mutant muscle, although ryanodine receptors other than the skeletal-muscle type seem to exist because the response to caffeine is retained. Our results show that the skeletal muscle ryanodine receptor is essential for both muscular maturation and E-C coupling, and also imply that the function of the skeletal muscle ryanodine receptor during E-C coupling cannot be substituted by other subtypes of the receptor.

Animals↗
PubMed1994

Ion permeation properties of the cloned mouse epsilon 2/zeta 1 NMDA receptor channel.

The heteromeric mouse epsilon 2/zeta 1 N-methyl-D-aspartate (NMDA) receptor was expressed in Xenopus oocytes, and its channel properties were studied using both the outside-out patch-clamp and two-microelectrode voltage-clamp techniques. In the cloned receptor channel, permeation properties of monovalent and divalent cations, and voltage-dependent block by Mg2+ were similar to those reported previously in the native NMDA receptor channels. The sequence of single-channel conductances for alkali metals was Rb+ > Cs+ approximately K+ > Na+ > Li+, whereas the sequence of relative permeabilities was Cs+ > Rb+ > K+ approximately Na+ > Li+. The single-channel conductances measured in isotonic Ca2+, Sr2+ and Ba2+ solutions were almost equal, and approximately one-fifth of the value in the Na+ solution, although the permeabilities for these alkaline earth cations were higher than for Na+. It is likely that Ca2+, Sr2+ and Ba2+ would enter the NMDA receptor channel more easily than Na+, but would bind to a site in the channel more tightly, the net effect being a reduced value of the current.

Animals↗
PubMed1994

Subunit composition at the single-cell level explains functional properties of a glutamate-gated channel.

The diversity of known glutamate-gated channels has been markedly increased by the discovery of multiple subunits and their spliced and edited variants. These subunits can potentially form different oligomeric complexes with diverging properties. A crucial question is therefore to determine the actual subunit composition of naturally occurring glutamate receptors. We have coupled patch-clamp recordings and reverse transcription followed by PCR amplification to correlate the presence of mRNAs for each subunit and the functional properties of native glutamate receptors at the single-cell level. In a homogeneous population of functionally identified hippocampal neurons (type II) in culture bearing a glutamate receptor of the AMPA subtype with a high calcium permeability, we found that, among the multiple subunits, only two, the flop forms of GluR1 and GluR4, were expressed. In particular, GluR2 was never detected. This composition explains the uncommon properties of AMPA receptors in type II neurons.

Animals↗
PubMed1993

Two distinct types of AMPA responses in cultured rat hippocampal neurons.

We previously found two distinct types of responses to kainate in cultured rat hippocampal neurons. The type I response is characterized by very little increase in Ca2+ permeability with an outward rectification in the current-voltage (I-V) relation of the kainate response. In contrast, the type II kainate response is characterized by prominent Ca2+ permeability and an inward rectification. These two types of responses were mimicked by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA). Furthermore, AMPA cross-desensitized both types of kainate responses. These results indicate that two functionally different types of AMPA/kainate receptors are expressed in hippocampal neurons.

Animals↗
PubMed1992

Calcium-dependent immediate feedback control of inositol 1,4,5-triphosphate-induced Ca2+ release.

The temporal and spatial distribution of increases in intracellular Ca2+ concentration is an important factor in cellular signal transduction. Inositol 1,4,5-trisphosphate (InsP3) plays a key part in agonist-induced Ca2+ release, which can take place abruptly and in a confined space by a mechanism that is not fully understood. Here we analyse the kinetics of InsP3-induced Ca2+ release following flash photolysis of caged InsP3 or caged Ca2+, and demonstrate that Ca(2+)-dependent immediate feedback control is an important determinant of the time course of Ca2+ release. The positive feedback mechanism is also important for the 'loading dependence' of InsP3-induced Ca2+ release. Furthermore, our results support the operation of positive cooperativity in channel opening and feedback control augments the steep InsP3 concentration-Ca2+ release relation. These inherent properties of InsP3-induced Ca2+ release are expected to give rise to temporally abrupt and/or spatially confined Ca2+ release within the cell.

Animals↗
PubMed1992

Enhancement of Ca2+-induced Ca2+ release in calpain treated rabbit skinned muscle fibers.

Calpain treatment of rabbit skinned muscle fibers resulted in proteolysis of junctional foot protein or Ca2+ release channel of the sarcoplasmic reticulum. Electrophoretic and immunoblot analyses indicate that calpain cleaves off approximately 130 kDa peptide from the N-terminus. After such treatment, Ca2+ capacity of the sarcoplasmic reticulum remained normal and both Ca2+ and adenine nucleotide dependence of Ca2+-induced Ca2+ release mechanism were retained. However, the Ca2+-activated Ca2+ release rate was increased by two fold after the proteolysis. The results suggest the presence of functional domains in the junctional foot protein, and the N-terminus domain controls the activity of the Ca2+ channel without changing Ca2+ and nucleotide sensitivities.

Animals↗
PubMed1992

Presence of functionally different compartments of the Ca2+ store in single intestinal smooth muscle cells.

Studies in smooth muscle bundles have shown the presence of functionally different compartments of Ca2+ store, one (S alpha) sensitive to both caffeine and inositol 1,4,5-trisphosphate (IP3), and the other (S beta) sensitive only to IP3. Ca2+ release in isolated single smooth muscle cells from guinea pig taenia caeci was studied to see if both compartments exist within a cell. Responses to caffeine and carbachol were consistently observed but were abolished after treatment with ryanodine, while intracellular application of IP3 induced Ca2+ release after the treatment, albeit smaller in size than control. Thus S alpha and S beta coexist in a single smooth muscle cell and agonist-induced Ca2+ release requires whole store to be loaded with Ca2+.

Animals↗
PubMed1992

[Effects of halothane, caffeine and ryanodine on the intracellular calcium store in blood mononuclear cells].

To evaluate the possibility of using blood cells in the screening test for susceptibility to malignant hyperthermia (MH), we examined the effect of halothane and caffeine on cytoplasmic free calcium concentration ([Ca]i) in mononuclear cells. Blood mononuclear cells were isolated from guinea pigs or normal human volunteers, loaded with fura-2 AM and changes in the calcium signal (340nm/380nm ratio) after the application of halothane and/or caffeine were measured. Halothane above 5 mM caused a large increase in [Ca]i, but this increase was mostly abolished by the removal of extra-cellular calcium using EGTA. On the other hand, caffeine caused no observable change in the calcium signal. Pre-treatment with ryanodine did not change the calcium signal brought about by halothane or ionomycin. We conclude from this study that there is no calcium-induced calcium release (CICR) mechanism detectable by this method in blood mononuclear cells. As we consider that the main cause of the typical MH is the abnormality in the CICR mechanism, it seems difficult to screen MH susceptibility by using blood mononuclear cells. Further studies will be necessary using MH susceptible swines or patients.

Animals↗
PubMed1991

Excitatory synapse in the rat hippocampus in tissue culture and effects of aniracetam.

Excitatory synaptic connections between rat hippocampal neurons were established in tissue culture. The electrophysiological and pharmacological properties of these synapses were studied with the use of the tight-seal whole-cell recording technique. The excitatory postsynaptic current (EPSC) in a dissociated CA1 neuron evoked by stimulation of an explant from the CA3/CA4 region of the hippocampus had two distinct components in Mg(2+)-free medium. The fast component was abolished by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (2 microM), whereas the slow component was abolished by the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovalerate (D-APV) (50 microM). In solution containing 1 mM Mg2+, the peak amplitude of the fast component was almost linearly related to the membrane potential. In contrast, the conductance change underlying the slow component of the EPSC was voltage-dependent with a region of negative-slope conductance in the range of -80 to -20 mV. A nootropic drug, aniracetam, increased both the amplitude and duration of the fast component of the EPSC in a concentration-dependent manner in the range of 0.1-5 mM, whereas it had no potentiating effect on the slow component. Aniracetam (0.1-5 mM) similarly increased current responses of the postsynaptic neuron to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA). Current responses to quisqualate and glutamate in the presence of D-APV were also potentiated by aniracetam. However, neither NMDA- nor kainate-induced current was potentiated by 1 mM aniracetam.

2-Amino-5-phosphonovalerate↗
PubMed1991

Effects of adenine nucleotides on inositol 1,4,5-trisphosphate-induced calcium release in vascular smooth muscle cells.

Effects of adenine nucleotides on the inositol 1,4,5-trisphosphate (IP3)-induced Ca release (IICR) mechanism were studied in smooth muscle cells of the guinea pig portal vein. A microfluorometry method of fura-2 was used to measure Ca release from saponin-skinned thin muscle strips (width approximately 200 microns, thickness 50-70 microns, length 2-3 mm). About 80% of ionomycin-releasable Ca store was sensitive to IP3, of which approximately 20% was also sensitive to caffeine. The rate of Ca release by 0.1 microM IP3 depended biphasically on ATP concentration in the absence of Mg2+; it was dose-dependently enhanced by ATP up to approximately 0.5 mM, and above this concentration the enhancement became smaller. However, the decline of enhancement of the IICR at the higher ATP concentrations was absent at IP3 concentrations greater than 1 microM. This suggests competitive antagonism between IP3 and ATP. Clear effects of ATP were observed not only at pCa 7 or 8, where the Ca-induced Ca release was not activated, but after a ryanodine treatment to excise the functional compartment that possessed the Ca-induced Ca release mechanism. ATP had no effect on the rate of Ca leakage in the absence of IP3 even at pCa 5.5 after the ryanodine treatment. Therefore, ATP has direct biphasic effects on the IP3-induced Ca release mechanism. The Ca release induced by 0.1 microM IP3 at pCa 7 was potentiated not only by ATP, but by 0.5 mM ADP, AMP, or beta, gamma-methyleneadenosine 5'-triphosphate. 0.5 mM GTP had only a little effect on the IP3-induced Ca release. These results extend the functional similarities between Ca- and IP3-induced Ca release mechanisms in that adenine nucleotides enhance Ca release. Millimolar concentration of ATP, which is present physiologically, will shift the dose-response relation of IP3 toward the higher IP3 concentration and enhance the maximal effect of IP3. Thus, ATP is expected to assist the Ca release by higher concentrations of IP3 while having less effect on the Ca release by low levels of IP3. These effects of ATP may be important in the switching of Ca release from the intracellular Ca store by IP3.

Adenine Nucleotides↗
PubMed1991

Two types of kainate response in cultured rat hippocampal neurons.

1. Two different types of kainate response were recorded in cultured rat hippocampal neurons with the use of the whole-cell and outside-out configurations of the patch-clamp technique. 2. There was an outward rectification in the current-voltage (I-V) plot of the kainate-induced current (type I response) in relatively large neurons bearing a morphological resemblance to young pyramidal cells. In smaller neurons with elliptical somata and fine neurites, the kainate response was characterized by a remarkable inward rectification in the I-V plot of the kainate-induced current and a significant permeability to Ca2+ (type II response). 3. Both type I and type II responses were negligible below 2 microM and almost saturated at 500 microM kainate. The concentrations producing half-maximal responses and the Hill coefficients were 68 microM and 1.76 and 56 microM and 1.21 for type I and type II responses, respectively. Both responses were suppressed similarly by the non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 4. The mean single-channel conductance (gamma) of the type II kainate response was estimated, from the relation between the whole-cell mean currents and current variances, to be 8.7 pS. The power spectrum for the current noise was fitted with the sum of two Lorentzians with cutoff frequencies (fc) of 61.1 +/- 1.4 and 327.8 +/- 10.5 Hz (n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1990

Biphasic Ca2+ dependence of inositol 1,4,5-trisphosphate-induced Ca release in smooth muscle cells of the guinea pig taenia caeci.

Ca2+ dependence of the inositol 1,4,5-trisphosphate (IP3)-induced Ca release was studied in saponin-skinned smooth muscle fiber bundles of the guinea pig taenia caeci at 20-22 degrees C. Ca release from the skinned fiber bundles was monitored by microfluorometry of fura-2. Fiber bundles were first treated with 30 microM ryanodine for 120 s in the presence of 45 mM caffeine to lock open the Ca-induced Ca release channels which are present in approximately 40% of the Ca store of the smooth muscle cells of the taenia. The Ca store with the Ca-induced Ca release mechanism was functionally removed by this treatment, but the rest of the store, which was devoid of the ryanodine-sensitive Ca release mechanism, remained intact. The Ca2+ dependence of the IP3-induced Ca release mechanism was, therefore, studied independently of the Ca-induced Ca release. The rate of IP3-induced Ca release was enhanced by Ca2+ between 0 and 300 nM, but further increase in the Ca2+ concentration also exerted an inhibitory effect. Thus, the rate of IP3-induced Ca release was about the same in the absence of Ca2+ and at 3 microM Ca2+, and was about six times faster at 300 nM Ca2+. Hydrolysis of IP3 within the skinned fiber bundles was not responsible for these effects, because essentially the same effects were observed with or without Mg2+, an absolute requirement of the IP3 phosphatase activity. Ca2+, therefore, is likely to affect the gating mechanism and/or affinity for the ligand of the IP3-induced Ca release mechanism. The biphasic effect of Ca2+ on the IP3-induced Ca release is expected to form a positive feedback loop in the IP3-induced Ca mobilization below 300 nM Ca2+, and a negative feedback loop above 300 nM Ca2+.

Animals↗