Biomedical subjects

M Iino

Publications and source records attributed to M Iino.

At least 91 records · Page 5Linked to original sources

PubMed1998

[Incidence of prolonged distal motor latency of the median nerve augments with the progression of diabetic polyneuropathy].

We investigated 303 diabetic patients in order to clarify the relationship between progression of diabetic polyneuropathy and conduction delay across the carpal tunnel. Distal latency ratio (DLR) was determined by comparison of distal motor latency of the median nerve with that of the ulnar nerve. Lower extremity polyneuropathy index (LPNI), expressed as a mean percentage of the normal for six indices over two nerves obtained by motor nerve conduction studies, was 82.9% on the average in the patients. Their DLR (1.44 +/- 0.24) was larger than the normal value (1.29 +/- 0.10). About 30% of the diabetics had abnormal DLR, especially in women its incidence was as high as 39%. The lower the LPNI level, the larger the incidence of abnormal DLR. In diabetic polyneuropathy patients peripheral nerves will become fragile, which might increase the incidence of conduction delay across the carpal tunnel. This phenomenon might also be called as 'double crush syndrome'.

Adult↗

PubMed1997

Asp278 of human beta-adrenergic receptor kinase 1 is essential for phosphorylation activity.

Asp278 of beta-adrenergic receptor kinase 1 (betaARK1) was suggested to play a key role in substrate recognition of beta2-adrenergic receptors in our previous study, in which a three-dimensional model of betaARK1 was studied in comparison with a crystal structure of PKA-PKI5-24 complex. In the present study, to confirm the molecular recognition mechanism at Asp278 of betaARK1, two mutants of betaARK1, D278R and D278A, were designed based on molecular modeling studies and produced by Sf-9 cells. As predicted by the molecular modeling study, the mutants showed no kinase activities while wild type betaARK1 phosphorylated beta2-adrenergic receptors in a concentration-dependent manner. These results strongly suggest the involvement of Asp278 in substrate recognition by betaARK1. The results also suggest a high reliability of the three-dimensional model of betaARK1.

Alanine↗

PubMed1997

Endothelium-dependent frequency modulation of Ca2+ signalling in individual vascular smooth muscle cells of the rat.

1. We visualized intracellular Ca2+ concentration ([Ca2+]i) changes, using fluo-3 as an indicator, of individual vascular smooth muscle cells and endothelial cells within intact rat tail arteries by confocal microscopy. 2. Using a piezo-driven objective, we focused on endothelial and smooth muscle cell layers alternately to obtain Ca2+ images of their cells. In the presence of 1 microM acetylcholine (ACh), individual endothelial cells responded with intermittent increases in the [Ca2+]i (Ca2+ oscillations). At the same time, the frequency of Ca2+ oscillations in smooth muscle cells induced by electrical stimulation of the perivascular sympathetic nerve was greatly decreased. 3. A [Ca2+]i rise during the oscillations in the endothelial cells propagated in the form of a wave along the long axis of the cells. 4. In the presence of a NO synthase inhibitor, no significant inhibitory effect of ACh on the Ca2+ signalling in the vascular smooth muscle cells was detected, although the Ca2+ oscillations in the endothelial cells persisted. 5. The inhibitory effect of ACh on the frequency of Ca2+ oscillations in the vascular smooth muscle cells was mimicked by 1 microM sodium nitroprusside, a NO donor. 6. These results indicate that Ca2+ waves and oscillations in vascular endothelial cells regulate NO production, which modulates vascular tone by decreasing the frequency of Ca2+ oscillations in smooth muscle cells activated by sympathetic agonists.

Acetylcholine↗

PubMed1997

Functional and morphological features of skeletal muscle from mutant mice lacking both type 1 and type 3 ryanodine receptors.

1. We generated mice with targeted disruptions in the genes for both ryanodine receptor type 1 (RyR-1) and type 3 (RyR-3) to study the functional roles of RyR subtypes in skeletal muscle. 2. In permeabilized myocytes lacking both the RyRs, the Ca(2+)-induced Ca2+ release (CICR) mechanism was completely lost, and caffeine failed to induce Ca2+ release. 3. Replacement of potassium methanesulphonate in an experimental intracellular solution with choline chloride resulted in Ca2+ release in the wild-type muscle but not in the mutant muscle lacking RyR-1. 4. The double-mutant mice exhibited more severe muscular degeneration than RyR-1-deficient mice with formation of large vacuoles and swollen mitochondria while structural coupling between T-tubules and the sarcoplasmic reticulum was retained. 5. These results demonstrate that CICR is mediated solely by RyR-1 and RyR-3 in skeletal muscle cells, and suggest that RyR-1 is involved in Cl(-)-induced Ca2+ release. The results also suggest the presence of molecular components other than RyRs responsible for the triad formation. RyR-3 may have a role in the normal morphogenesis of skeletal muscle cells, although functionally it can be replaced by RyR-1.

Animals↗

PubMed1997

A region of the ryanodine receptor critical for excitation-contraction coupling in skeletal muscle.

Ca2+ release mediated by the ryanodine receptor (RyR) regulates many important cell functions including excitation-contraction (E-C) coupling in skeletal muscle, by which membrane depolarization controls the opening of RyR via the dihydropyridine receptor. Among the three RyR subtypes, RyR-1 mediates skeletal muscle E-C coupling, whereas RyR-2 and RyR-3 cannot substitute for RyR-1. We carried out expression experiments using cultured mutant skeletal myocytes not having intrinsic intracellular Ca2+ release channels to study the structure-function relationship of amino acid residues 1303-1406 in RyR-1 (D2 region). In this region the amino acid sequences are highly divergent between RyR-1 and RyR-2, and the corresponding sequence is lacking in RyR-3. Expression of RyR-1 but not of RyR-2 rescued E-C coupling in the mutant cells. Deletion of either the entire D2 region or its N-terminal half from RyR-1 preserved the function of RyR-1 as a Ca2+ release channel but resulted in the loss of E-C coupling. Substitution of the D2 region for the corresponding sequence of RyR-2 had no effect on the function of RyR-1. These results indicate that the presence of the D2 region is critical for E-C coupling in skeletal muscle, although the D2 region alone cannot determine the functional difference between RyR-1 and RyR-2.

Amino Acid Sequence↗

PubMed1997

Permeation properties of Na+ and Ca2+ ions through the mouse epsilon2/zeta1 NMDA receptor channel expressed in Xenopus oocytes.

Ion permeation properties of the mouse e2/zeta1 NMDA receptor channel expressed in Xenopus oocytes were studied using the outside-out patch-clamp technique. In symmetrical Na+ solutions, the single-channel I-V relations were almost linear at low electrolyte concentrations, but rectified inwardly for Na+ concentrations above 50 mm. In symmetrical Na+ solutions, the "zero-current conductance" increased with Na+ concentration and saturated according to a hyperbolic curve, the half-maximal saturating activity, KM(Na), being 14.2 mm and the maximal conductance, Gmax(Na), 53.9 pS. When Ca2+ was present with Na+ in the external solution, the single-channel current was lower than in pure Na+, although the reversal potential indicated a higher permeability for Ca2+ than for Na+. Using ion activities, PCa/PNa was found to be about 17. The I-V data were fitted with a model based on the Eyring's rate theory, assuming a one-ion pore with three energy barriers and two sites. The KM(Ca) and Gmax (Ca) were 76.5 microm and 21.2 pS, respectively. According to the estimated rate constants, KM for Ca2+ is mainly determined by the binding strength of a site located 80% away from the channel opening at the external membrane-solution interface, a position similar to that postulated previously for the Mg2+ blocking site.

Animals↗

PubMed1997

Phototropism of rice (Oryza sativa L.) coleoptiles: fluence-response relationships, kinetics and photogravitropic equilibrium.

Phototropism of rice (Oryza sativa L.) coleoptiles induced by unilateral blue light was characterized using red-light-grown seedlings. Phototropic fluence-response relationships, investigated mainly with submerged coleoptiles, revealed three response types previously identified in oat and maize coleoptiles: two pulse-induced positive phototropisms and a phototropism that depended on stimulation time. The effective ranges of fluences and fluence rates were comparable to those reported for maize. Compared with oats and maize, however, curvature responses in rice were much smaller and coleoptiles straightened faster after establishing the maximal curvature. When stimulated continuously, submerged coleoptiles developed curvature slowly over a period of 6 h, whereas air-grown coleoptiles, which showed smaller phototropic responsiveness, established a photogravitropic equilibrium from about 4 h of stimulation. The plot of the equilibrium angle against log fluence rates yielded a bell-shaped optimum curve that spanned over a relatively wide fluence-rate range; a maximal curvature of 25 degrees occurred at a fluence rate of 1 micromole m-2 s-1. This optimum curve apparently reflects the light sensitivity of the steady-state phototropic response.

Cotyledon↗

PubMed1997

Blocking effect of 1-naphthyl acetyl spermine on Ca(2+)-permeable AMPA receptors in cultured rat hippocampal neurons.

Effects of 1-naphthyl acetyl spermine (NASPM), a synthetic analogue of Joro spider toxin (JSTX), on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors were studied in cultured rat hippocampal neurons using the whole-cell patch clamp technique. A population of cultured neurons had AMPA receptors with a strong inward rectification and a high permeability to Ca2+ (type II neurons). Whereas most neurons (type I neurons) had AMPA receptors with a slight outward rectification and little Ca2+ permeability. NASPM selectively suppressed the inwardly rectifying and Ca(2+)-permeable AMPA receptors expressed in type II neurons. It had no effect on AMPA receptors in type I neurons. The blocking effect of NASPM on the Ca(2+)-permeable AMPA receptors was use and voltage-dependent. When the effect of NASPM reached a steady state, current responses induced by ionophoretic applications of kainate, a non-desensitizing agonist of AMPA receptors, in type II neurons were suppressed by NASPM in a dose-dependent manner at -60 mV (IC50 0.33 microM, and Hill coefficient 0.94). The response to kainate recovered partially after washing out NASPM. NASPM did not affect the Ca(2+)-permeable AMPA receptors when the neuronal membrane was held at potentials more positive than +40 mV. Furthermore, the blockade by NASPM which was attained at negative potentials was transiently removed by shifting membrane potential to +60 mV for 5 s together with a single ionophoretic application of kainate. NASPM would be useful as a pharmacological tool for elucidating both physiological and pathological significances of Ca(2+)-permeable AMPA receptors in the CNS.

Animals↗

PubMed1997

Gravitropism of oat and wheat coleoptiles: dependence on the stimulation angle and involvement of autotropic straightening.

Gravitropism of oat (Avena sativa L.) and wheat (Triticum aestivum L.) coleoptiles was investigated in relation to the displacement angle or to the initially set stimulation angle (SA). We measured curvature rates at the early phase of curvature, before it was affected by the drop in SA resulting from the curvature response itself. The plot of the rates against the sines of initial SAs revealed similar curves for oats and wheat, which approached saturation as the sine increased to unity. The two species and previously analyzed rice [Iino et al. (1996) Plant Cell Environ. 19: 1160] appeared to have similar gravisensitivities. Initial SAs below and over 90 degrees yielded comparable rates when the sine values were the same, indicating that the extent of gravitropism is determined by the gravity component perpendicular to the organ's long axis. Long-term curvature kinetics at different SAs indicated that the net curvature rate dropped sharply before the tip reached the vertical position and then the tip approached the vertical slowly, with clear oscillatory movements in the case of wheat. During this late curvature phase, the coleoptile straightened gradually, although none of its parts had yet reached the vertical. When rotated on horizontal clinostats or displaced upwards to reduce SA in the late curvature phase, coleoptiles bent in the opposite direction. These results demonstrated that autotropism counteracts gravitropism to straighten coleoptiles.

Avena↗

PubMed1997

Restoration of phototropic responsiveness in decapitated maize coleoptiles.

The literature indicates that the tip of maize (Zea mays L.) coleoptiles has the localized functions of producing auxin for growth and perceiving unilateral light stimuli and translocating auxin laterally for phototropism. There is evidence that the auxinproducing function of the tip is restored in decapitated coleoptiles. We examined whether the functions for phototropism are also restored by using blue-light conditions that induced a first pulse-induced positive phototropism (fPIPP) and a time-dependent phototropism (TDP). When the apical 5 mm, in which photosensing predominantly takes place, was removed, no detectable fPIPP occurred even if indole-3-acetic acid (lanolin mixture) was applied to the cut end. However, when the blue-light stimulation was delayed after decapitation, fPIPP became inducible in the coleoptile stumps supplied with indole-3-acetic-acid/lanolin (0.01 mg g-1), indicating that phototropic responsiveness was restored. This restoration progressed 1 to 2 h after decapitation, and the curvature response became comparable to that of intact coleoptiles. The results for TDP were qualitatively similar, but some quantitative differences were observed. It appeared that the overall TDP was based on a major photosensing mechanism specific to the tip and on at least one additional mechanism not specific to the tip, and that the tip-specific TDP was restored in decapitated coleoptiles with kinetics similar to that for fPIPP. It is suggested that the photoreceptor system, which accounts for fPIPP and a substantial part of TDP, is regenerated in decapitated coleoptiles, perhaps together with the mechanism for lateral auxin translocation.

Cotyledon↗

PubMed1996

Factor VII central. A novel mutation in the catalytic domain that reduces tissue factor binding, impairs activation by factor Xa, and abolishes amidolytic and coagulant activity.

Factor VII is a vitamin K-dependent zymogen of a serine protease that participates in the initial phase of blood coagulation. A factor VII molecular variant (factor VII Central) was identified in a 24-year-old male with severe factor VII deficiency and whose plasma factor VII antigen was 38% of normal, but expressed <1% factor VII procoagulant activity. DNA sequence analysis of the patient's factor VII gene revealed a thymidine to cytidine transition at nucleotide 10907 in exon VIII that results in a novel amino acid substitution of Phe328 to Ser. The patient was homozygous for this mutation, whereas each parent of the patient was heterozygous for this mutation. To investigate the molecular properties of this variant, a recombinant F328S factor VII mutant was prepared and analyzed in relation to wild-type factor VII. F328S factor VII exhibited <1% factor VII procoagulant activity and a 2-fold decreased affinity for tissue factor and failed to activate factor X or IX in the presence of tissue factor following activation by factor Xa. In addition, F328S factor VIIa exhibited no detectable amidolytic activity in the presence of tissue factor. The rate of F328S factor VII activation by factor Xa was markedly decreased relative to the rate of wild-type factor VII activation as revealed by densitometry scanning of SDS gels. Temporal analysis of this reaction by SDS-polyacrylamide gel electrophoresis also revealed the formation of two novel F328S factor VII degradation products (40 and 9 kDa) resulting from factor Xa proteolysis of the Arg315-Lys316 peptide bond in intact F328S factor VII. Computer modeling and molecular dynamics simulations of the serine protease domain of factor VIIa suggested that the inability of F328S factor VIIa to cleave substrates may result from the apparent formation of a hydrogen bond between Tyr377 and Asp338, a residue at the bottom of the substrate-binding pocket important for the interaction of substrate arginine side chains with the enzyme. These findings suggest that Phe328, which is conserved in prothrombin, factor IX, factor X, factor VII, and trypsin, is important for factor VIIa catalysis.

Adult↗

PubMed1996

Subtype specificity of the ryanodine receptor for Ca2+ signal amplification in excitation-contraction coupling.

In excitable cells membrane depolarization is translated into intracellular Ca2+ signals. The ryanodine receptor (RyR) amplifies the Ca2+ signal by releasing Ca2+ from the intracellular Ca2+ store upon receipt of a message from the dihydropyridine receptor (DHPR) on the plasma membrane in striated muscle. There are two distinct mechanisms for the amplification of Ca2+ signalling. In cardiac cells depolarization-dependent Ca2+ influx through DHPR triggers Ca2+-induced Ca2+ release via RyR, while in skeletal muscle cells a voltage-induced change in DHPR is thought to be mechanically transmitted, without a requirement for Ca2+ influx, to RyR to cause it to open. In expression experiments using mutant skeletal myocytes lacking an intrinsic subtype of RyR (RyR-1), we demonstrate that RyR-1, but not the cardiac subtype (RyR-2), is capable of supporting skeletal muscle-type coupling. Furthermore, when RyR-2 was expressed in skeletal myocytes, we observed depolarization-independent spontaneous Ca2+ waves and oscillations, which suggests that RyR-2 is prone to regenerative Ca2+ release responses. These results demonstrate functional diversity among RyR subtypes and indicate that the subtype of RyR is the key to Ca2+ signal amplification.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1996

Voltage-dependent blockage of Ca(2+)-permeable AMPA receptors by joro spider toxin in cultured rat hippocampal neurones.

1. The effect of synthetic joro spider toxin (JSTX-3) on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels in cultured rat hippocampal neurones was investigated using the whole-cell patch-clamp technique. 2. A population of cultured neurones had AMPA receptors with strong inward rectification and substantial Ca2+ permeability (type II neurones), whereas most neurones (type I neurones) had slight outward rectification and little Ca2+ permeability. JSTX-3 selectively suppressed the inwardly rectifying and Ca(2+)-permeable AMPA receptors expressed in type II neurones without affecting AMPA receptors in type I neurones. 3. The effect of JSTX-3 on the Ca(2+)-permeable AMPA receptors was use and voltage dependent. In the steady state, current responses induced by ionophoretic applications of kainate (a non-desensitizing agonist of AMPA receptors) were suppressed by the toxin in a dose-dependent manner at negative potentials (IC50 = 56 nM at -60 mV). 4. At the standard membrane potential (-60 mV), recovery from the blockage by JSTX-3 was very slow. Even after washout for more than 7 min, the recovery was only partial. However, the blockage was completely removed immediately after application of a +60 mV voltage pulse for 5 s in conjunction with a single ionophoretic application of kainate.

Animals↗

PubMed1996

Native structure and arrangement of inositol-1,4,5-trisphosphate receptor molecules in bovine cerebellar Purkinje cells as studied by quick-freeze deep-etch electron microscopy.

We used quick-freeze deep-etch replica electron microscopy to visualize the native structure of inositol-1,4,5-trisphosphate receptor (IP3R) in the cell. In the dendrites of Purkinje neurons of bovine cerebellum there were many vesicular organelles whose surfaces were covered with a two-dimensional crystalline array of molecules. Detailed examination of the cytoplasmic true surface of such vesicles in replica revealed that the structural unit, identified as IP3R by immunocytochemistry and subsequent Fourier analysis, is a square-shaped assembly and is aligned so that the side of the square is inclined by approximately 20 degrees from the row-line of the lattice. Comparison with the ryanodine receptor (RyaR), another intracellular Ca2+ channel on the endoplasmic reticulum, suggested that IP3R, unlike RyaR, has a very compact structure, potentially reflecting the crucial difference in the function of the cytoplasmic portion of the molecule.

Animals↗

PubMed1996

Generation and characterization of mutant mice lacking ryanodine receptor type 3.

The ryanodine receptor type 3 (RyR-3) functions as a Ca2+-induced Ca2+ release (CICR) channel and is distributed in a wide variety of cell types including skeletal muscle and smooth muscle cells, neurons, and certain non-excitable cells. However, the physiological roles of RyR-3 are totally unclear. To gain an insight into the function of RyR-3 in vivo, we have generated mice lacking RyR-3 by means of the gene targeting technique. The mutant mice thus obtained showed apparently normal growth and reproduction. Although Ca2+-induced Ca2+ release from intracellular Ca2+ stores of the mutant skeletal muscle differed in Ca2+ sensitivity from that of wild-type muscle, excitation-contraction coupling of the mutant muscle seemed to be normal. Moreover, we could not find any significant disturbance in the smooth muscle and lymphocytes from the mutant mice. On the other hand, the mutant mice showed increased locomotor activity, which was about 2-fold greater than that of the control mice. These results indicate that the loss of RyR-3 causes no gross abnormalities and suggest that the lack of RyR-3-mediated Ca2+ signaling results in abnormalities of certain neurons in the central nervous system.

Animals↗

PubMed1996

Sphingosine-containing phospholipid vesicles support human factor VII autoactivation in the absence of tissue factor.

We studied the effects of lipid membrane composition on factor VII autoactivation and observed that factor VII was activated in the presence of phospholipid vesicles containing sphingosine. The time course for the factor VII activation was sigmoidal and the duration of the initial lag phase was decreased by the addition of exogenous factor VIIA. Kinetic studies revealed that factor VII activation in the presence of sphingosine-containing phospholipids can be defined by a second-order reaction mechanism with an apparent second-order rate constant of 1.1x10(4) M(-1)s(-1). The sphingosine-mediated factor VII autoactivation rate was dependent on the concentration of calcium ions and sphingosine content of the vesicles. Neither bovine serum albumin-conjugated sphingosine nor sphingosine analogues (ceramide, sphingomyelin) affected the factor VII autoactivation rate.

Calcium↗

PubMed1996

Distribution of neurones expressing inwardly rectifying and Ca(2+)-permeable AMPA receptors in rat hippocampal slices.

1. Current-voltage (I-V) relationships and Ca2+ permeability of receptor channels activated by bath application of kainate, a non-desensitizing agonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, were examined in various types of neurones in hippocampal slices of 5- to 13-day-old rats by using the tight-seal patch clamp recording technique. 2. Three types of responses were observed: type I response with outwardly rectifying I-V relationship, type II response with I-V relationship of marked inward rectification, and intermediate response with I-V relationship of weaker inward rectification. Neurones with type I, type II and intermediate I-V relationships of kainate responses were referred to as type I, type II and intermediate neurones, respectively. 3. Permeability of Ca2+ ions was estimated by the reversal potential of kainate response in the outside-out patch in Na(+)-free extracellular solution containing 100 mM Ca2+. The reversal potentials were -44.4 +/- 14.0 mV (mean +/- S.D.) for type I (n = 7), +11.8 +/- 3.6 mV for type II (n = 5), and -8.7 +/- 7.4 mV for the intermediate neurones (n = 7). The values of PCa/PCs, the ratios of the permeability coefficients of Ca2+ and Cs+, estimated according to the constant-field equation were 0.08 for type I, 1.71 for type II, and 0.50 for the intermediate neurones. 4. Type II and intermediate responses were observed mainly in non-pyramidal neurones in various areas of the hippocampus, most frequently observed in the stratum molecular of the dentate gyrus and in the stratum radiatum and the stratum lacunosum-molecular of both the CA1 and CA3 regions. Both type II and intermediate neurones stained with biocytin had round- or ellipsoidal-shaped somata and issued divergent axonal projections to the surrounding structures. 5. Excitatory postsynaptic currents (EPSCs) recorded in type II neurones had 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)-sensitive fast and D-2-amino-5-phosphonovalerate (APV)-sensitive slow components. The I-V relationship of the fast component showed a strong inward rectification, indicating that inwardly rectifying AMPA receptors are involved in excitatory synaptic transmission.

2-Amino-5-phosphonovalerate↗

PubMed1996

Spermine blocks synaptic transmission mediated by Ca(2+)-permeable AMPA receptors.

AMPA-gated glutamate receptors with outward rectification (type I receptors) are almost impermeable to Ca2+, while those with strong inward rectification (type II receptors) have high Ca2+ permeability. In the present study current responses in rat hippocampal neurones mediated by type II AMPA receptors were blocked by application of spermine to the external solution (IC50 = 170 microM), but those mediated by type I AMPA receptors were not affected. Furthermore, in putative non-pyramidal neurones in rat hippocampal slices, EPSCs mediated by type II AMPA receptors were markedly reduced by 1mM spermine, while those mediated by type I AMPA receptors were much less affected. Thus, external spermine exerts differential blocking action on the two different types of AMPA receptors.

Animals↗