Biomedical subjects

M Iino

Publications and source records attributed to M Iino.

At least 127 records · Page 7Linked to original sources

PubMed1994

Primary structure and distribution of ryanodine-binding protein isoforms of the bullfrog skeletal muscle.

We have cloned two groups of cDNAs which encode isoforms of ryanodine-binding protein/Ca2+ release channel of the bullfrog skeletal muscle sarcoplasmic reticulum. One of the cDNA groups encodes the protein of 5,037 (or 5,031 with a deletion) amino acids with a molecular weight of 571,262 (or 570,607), which is identified as the alpha-isoform of the ryanodine-binding protein based on the amino acid sequence of three tryptic fragments of the purified protein. The other group of cDNAs encodes the protein of 4,868 amino acids with molecular weight of 553,029, which contains the sequences of three proteolytic fragments derived from the beta-isoform protein. About 70% of the amino acid sequence identity is present between alpha- and beta-isoforms of the bullfrog. The primary structure of the alpha-isoform is highly (80%) homologous to the ryanodine-binding protein cloned from rabbit skeletal muscle (type 1). The beta-isoform, on the other hand, is more than 85% identical with that from the rabbit brain (type 3), while it has only 67% overall identity with type 1. Analyses of RNA from various tissues of the bullfrog demonstrate that the beta-isoform is widely expressed, while the alpha-isoform is expressed mainly in skeletal muscle. A phylogenetic analysis of the ryanodine-binding protein/Ca2+ release channel family suggests that the various types of Ca2+ release channels have evolved from an ancestor gene. Possible differential roles of alpha- and beta-isoforms of ryanodine-binding protein in Ca2+ release mechanisms including skeletal muscle excitation-contraction coupling were discussed.

Animals↗

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

Relationship between calcium permeability and rectification properties of AMPA receptors in cultured rat hippocampal neurons.

Cultured rat hippocampal neurons were classified into three groups on the basis of the functional properties of their AMPA-subtype glutamate receptors. The type I neuron had AMPA receptors with an outwardly rectifying I-V relation and little permeability to Ca2+ whereas the AMPA receptors in the type II neuron were characterized by marked inward rectification and high Ca2+ permeability. In the third type of neuron, the responses of AMPA receptors exhibited intermediate properties in both I-V relation and Ca2+ permeability. We suggest that these intermediate properties in the third type of neuron reflect the coexistence of Ca(2+)-permeant and Ca(2+)-impermeant AMPA receptors.

Animals↗

PubMed1994

pH dependence of inositol 1,4,5-trisphosphate-induced Ca2+ release in permeabilized smooth muscle cells of the guinea-pig.

1. The dependence on pH of inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release was studied in saponin-skinned smooth muscle cells from guinea-pig portal vein, using the indicator fura-2 to monitor Ca2+ release. 2. Increasing pH between 6.7 and 7.3 enhanced the rate of IP3-induced Ca2+ release at all the Ca2+ concentrations above 30 nM without changing the bell-shaped dependence of the Ca2+ release rate on Ca2+ concentration with a peak near 300 nM. 3. The ascending limb of the biphasic Ca2+ dependence was shifted slightly toward the lower Ca2+ concentration at pH 7.3, suggesting an increase in the Ca2+ sensitivity of IP3-induced Ca2+ release at the higher pH. 4. With the elevation in pH from 6.7 to 7.3 at 100 nM Ca2+, about 7-fold higher IP3 concentration was required to release half of the Ca2+ in the store within 15 s. This pH-dependent change in the IP3 sensitivity was smaller at 1 microM Ca2+ and was indiscernible in the absence of Ca2+. 5. These results suggest that H+ may inhibit binding of IP3 and Ca2+ to the modulator sites of the Ca2+ release mechanism. However, these effects on the binding sites may not fully explain the complex effect of pH, and there may be pH-dependent step(s) involved in the gating mechanism of IP3 channels. The present study demonstrates the importance of pH as a modulator of IP3-induced Ca2+ release.

Animals↗

PubMed1994

Transition from Lorentzian to Gaussian line shape of magnetization transfer spectrum in bovine serum albumin solutions.

Magnetization transfer experiments using an off-resonance irradiation technique were performed on bovine serum albumin solutions by varying the irradiation frequency and the concentration. A transition of the magnetization transfer spectrum from Lorentzian to Gaussian line shape was observed around the critical concentration of 6.2 mmoles of protein to kg of solution. Observed magnetizations were well expressed by the rate equations of populations for spins below and above the transition, which yielded the magnetization transfer rates, the intrinsic relaxation rates of both protein and water protons, and the effective tumbling time and the rigid line width of the protein. The result showed that the estimates of the values for magnetization transfer rate do not change once the critical concentration is reached.

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

Feedback control of inositol trisphosphate signalling bycalcium.

Inositol 1,4,5-trisphosphate (InsP3)-induced Ca2+ release depends on the cytoplasmic concentration of Ca2+ in a biphasic manner: activated with the increase in Ca2+ up to approximately 300 nM and inhibited by its further increase. Kinetic studies of the Ca2+ release with rapid increase in Ca2+ or InsP3 using respective caged compounds indicated that the effects of Ca2+ appear immediately upon change in the Ca2+ concentration. Recovery from the Ca(2+)-dependent inhibition seemed also rapid after reduction in the Ca2+ concentration. These results indicate that there is a Ca(2+)-mediated positive feedback control of InsP3-induced Ca2+ release below 300 nM Ca2+. This feedback control seems to explain, at least partly, the phenomenon that InsP3 is more effective in the Ca2+ stores with greater Ca2+ loading. The Ca(2+)-mediated feedback control is also expected to give rise to temporally or spatially confined Ca2+ release as well as Ca2+ wave within the cells.

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↗

PubMed1994

The role of human factor X activation peptide in activation of factor X by factor IXa.

We studied the interaction of factor X activation peptide (XAP) with factor IXa and factor Xa and the effect of XAP on factor IXa-catalyzed activation of factor X. XAP associated with factor Xa in the presence of 5 mM Ca2+ was dissociated from factor Xa by gel chromatography using Ultrogel AcA54 in 5 mM EDTA, or in 8 M urea-0.1% SDS. An exogenous isolated XAP inhibited the factor IXa-catalyzed factor X activation both in the presence and absence of factor VIIIa. 4-Amidinophenylmethylsulfonyl (aPMS)-factor Xa independent of XAP also inhibited the factor X activation more effectively than XAP alone in the presence of factor VIIIa. However, aPMS-factor Xa independent of XAP hardly inhibited the factor X activation in the absence of factor VIIIa. The binding of 125I-labeled factor X to the aPMS-factor IXa fixed to a microwell plate was inhibited by unlabeled factor X or XAP, but not by aPMS-factor Xa with or without XAP. Factor IXa directly bound to XAP and aPMS-factor Xa with XAP, but did not bind to aPMS-factor Xa without XAP. These findings suggest that the region of XAP in factor X directly interacts with factor IXa, and factor Xa region other than XAP interacts with factor VIIIa. Desialation or deletion of N-linked carbohydrates of XAP reduced the inhibitory activity of XAP for the factor X activation by factor IXa to approximately 50% of that of the intact XAP. This suggests that the sialic acids in the carbohydrate chains of the XAP region partly contribute to the interaction with factor IXa during its activation.

Amino Acid Sequence↗

PubMed1994

Effects of cyclopiazonic acid on rhythmic contractions in uterine smooth muscle bundles of the rat.

1. We studied the effects of cyclopiazonic acid (CPA) on rhythmic contractions and on Ca2+ uptake by the intracellular stores in longitudinal muscle strips of the rat uterus at 30 degrees C. 2. Oxytocin (1 microM) in Ca(2+)-free solution induced a transient rise in the intracellular Ca2+ concentration ([Ca2+]i) and contraction after Ca2+ loading of the stores in high-K(+)- and Ca(2+)-containing solution. CPA inhibited oxytocin-induced Ca2+ release and contraction, the half and full inhibitory concentrations of CPA being 0.3 and 10 microM, respectively. In contrast, addition of CPA after Ca2+ loading exerted no significant inhibitory effects. 3. Oxytocin (10 nM) applied in Ca(2+)-containing solution induced rhythmic increases in both force and [Ca2+]i. CPA (10 microM) had no effect on oxytocin-induced rhythmic contractions. 4. At a high concentration (300 microM), CPA inhibited the rhythmic contractions induced by 10 nM oxytocin; the frequency and the peak height were decreased, and in many bundles contractions were completely abolished. These inhibitory effects were reversed after CPA washout. 5. CPA (300 microM) inhibited the rate of rise of [Ca2+]i due to depolarization induced by high-K(+)-containing solution. 6. These results suggest that low concentrations of CPA inhibit the loading of Ca2+ into intracellular stores in intact tissue strips, and that the Ca2+ stores are not directly involved in the uterine rhythmic contractions. It is also suggested that a high concentration of CPA inhibits the mechanism that is responsible for the generation of rhythmic contractions as well as voltage-dependent Ca2+ channels.

Animals↗

PubMed1993

Critical intracellular Ca2+ concentration for all-or-none Ca2+ spiking in single smooth muscle cells.

Neurotransmitters induce contractions of smooth muscle cells initially by mobilizing Ca2+ from intracellular Ca2+ stores through inositol 1,4,5-trisphosphate (InsP3) receptors. Here we studied roles of the molecules involved in Ca2+ mobilization in single smooth muscle cells. A slow rise in cytoplasmic Ca2+ ([Ca2+]i) in agonist-stimulated smooth muscle cells was followed by a wave of rapid regenerative Ca2+ release as the local [Ca2+]i reached a critical concentration of approximately 160 nM. Neither feedback regulation of phospholipase C nor caffeine-sensitive Ca(2+)-induced Ca2+ release was found to be required in the regenerative Ca2+ release. These results indicate that Ca(2+)-dependent feedback control of InsP3-induced Ca2+ release plays a dominant role in the generation of the regenerative Ca2+ release. The resulting Ca2+ release in a whole cell was an all-or-none event, i.e. constant peak [Ca2+]i was attained with agonist concentrations above the threshold value. This finding suggests a possible digital mode involved in the neural control of smooth muscle contraction.

Animals↗

PubMed1993

Caffeine inhibits Ca(2+)-mediated potentiation of inositol 1,4,5-trisphosphate-induced Ca2+ release in permeabilized vascular smooth muscle cells.

We studied the effects of caffeine on inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release in saponin-permeabilized smooth muscle cells. The Ca2+ concentration in the vicinity of the Ca2+ store was strongly buffered to exclude the secondary effect of Ca2+ on the Ca2+ release. 2 mM caffeine shifted the IP3 concentration-Ca2+ release relation at 100 nM Ca2+ to the higher IP3 concentration without decreasing the steepness of the relation. The ascending limb of the biphasic Ca2+ dependence of IP3-induced Ca2+ release was shifted to the higher Ca2+ concentration by 2 mM caffeine. However, caffeine showed little inhibitory effect in the absence of Ca2+. These results indicate that caffeine inhibits IP3-induced Ca2+ release only when the Ca2+ release is potentiated by Ca2+.

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↗

PubMed1993

Characterization of functionally important regions of tissue factor by using monoclonal antibodies.

Tissue factor is a cellular membrane glycoprotein that acts as a cofactor for Factor VIIa-catalyzed activation of Factors X and IX in the extrinsic blood coagulation pathway. We prepared fourteen murine monoclonal antibodies to human tissue factor (designated MTF-1 to -14), and purified tissue factor from human placenta by immunoaffinity chromatography using the antibody-coupled Sepharose 4B. The antibodies were characterized for inhibitory activity against the activation of Factor X by a complex of Factor VIIa and purified placental tissue factor or a recombinant mutant tissue factor whose transmembrane and cytoplasmic domains were deleted. Four MTFs (MTF-6, -7, -8, and -14) markedly inhibited the cofactor activity of tissue factor by directly blocking the interaction with Factor VIIa. Three other MTFs (MTF-1, -4, and -9) moderately inhibited the cofactor activity of the mutant tissue factor, presumably by diminishing the interaction between the extracellular region of the tissue factor and phospholipids. Both groups of MTFs inhibited the cofactor activity of the mutant tissue factor in Factor X activation by Factor VIIa in the absence of phospholipids. These findings suggest that the former four MTFs recognize the binding site for Factor VIIa and the latter three MTFs recognize the site for Factor X in the extracellular region of tissue factor. These MTFs are useful to purify tissue factor by immunoaffinity chromatography and to study the structure-function relationship of tissue factor, and may be useful to establish an immunoassay of tissue factor in body fluids.

Animals↗

PubMed1993

Effects of ryanodine on the properties of Ca2+ release from the sarcoplasmic reticulum in skinned skeletal muscle fibres of the frog.

1. We studied the effects of ryanodine on the functions of the sarcoplasmic reticulum (SR) in skinned muscle fibres from Xenopus laevis. 2. Ryanodine treatment decreased the Ca2+ uptake capacity of the SR in a fixed Ca2+ loading condition. The extent of the decrease in the SR Ca2+ uptake capacity was closely correlated with the activity of the Ca(2+)-induced Ca2+ release (CICR) during the ryanodine treatment. This suggests, in agreement with the previous biochemical results, that ryanodine acts on the CICR channels when they are open. 3. The rate of Ca2+ leakage from the SR increased after ryanodine treatment. However, the leakage rate constants were independent of the degree of the loss of SR Ca2+ uptake capacity by the ryanodine treatment. This is inconsistent with the notion that the SR is a single uniform compartment and that the decline in the SR Ca2+ uptake capacity is a result of the increase in the Ca2+ leakage. 4. Partial recovery of the Ca2+ uptake capacity of the ryanodine-treated SR was observed when Ca2+ loading was carried out in the presence of 10 mM procaine. This indicates that procaine partially blocks the open-locked channels. 5. After Ca2+ loading in the presence of procaine, removal of procaine induced a rapid release of Ca2+ from the SR through the open-locked channels. This rapid release was dependent both on the adenine nucleotide concentration and on the Ca2+ concentration. Thus, the 'open-locked' CICR channels are still regulated by Ca2+ and adenine nucleotides.

Animals↗

PubMed1993

[Ca2+ release mechanism studied in single isolated smooth muscle cells].

This paper briefly reviews our current effort to study the Ca2+ mobilization mechanism in enzymatically dispersed single smooth muscle cells. Each single cell obtained from guinea pig taenia caeci possesses two types of Ca2+ stores, one (S alpha) with both Ca(2+)-induced and IP3-induced Ca2+ release mechanisms and the other (S beta) with only IP3-induced Ca2+ release mechanism. After depletion of S alpha either with ryanodine treatment or with caffeine pretreatment, carbachol failed to induce Ca2+ release, while intracellular application of IP3 did induce Ca2+ release. Our results suggest that the difference between the agonist- and IP3-induced responses can be resolved by obligatory involvement of positive feedback control of IP3-induced Ca2+ release in the agonist-induced Ca2+ release. Furthermore, we were able to demonstrate that the dose-response relation in single cells shows an all-or-none feature, which seems at least partly due to the feedback control of Ca2+ release. We discuss the reasons why graded dose-response relation is obtained in bundles of smooth muscles, while the response of single cells is an all-or-none type.

Animals↗

PubMed1993

[Evaluation of home blood pressure measurement by a correlation study between home blood pressure and ambulatory blood pressure].

To evaluate the self-measurement of blood pressure at home, a comparative study was performed among home (Home BP), ambulatory (24-hour BP) and office blood pressure in essential hypertensive patients. In all patients, Home BP was self measured by themselves twice a day for a month. 24-hour BP was measured once during the period of self-Home BP measurement. Office BP was measured twice a month. The average of Office BP (147/92 mmHg) and Home BP (145/89 mmHg) were higher than the average of 24 hour BP (131/82 mg). For systolic BP, about two weeks self-measurement of BP at home just after waking elicited a very high correlation between home and average 24-hour BP (r = 0.82), whereas for diastolic BP the r value was moderate (r = 0.61). In patients (n = 22) treated with antihypertensives, furthermore, the correlation coefficient between home and 24-hour BP for systolic BP reached 0.89, which is higher than in all patients (n = 28). The average value of BP measured just after waking at home elicited a higher correlation with the average value of 24-hour BP compared with that measured before going to bed. The results suggest that in essential hypertensive patients who are treated with antihypertensives, to measure BP just after waking for about two weeks at home could help clinicians to evaluate and predict the value of average 24-hour BP.

Adult↗

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↗