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H Suga

Publications and source records attributed to H Suga.

At least 55 records · Page 3Linked to original sources
PubMed1999

Multiple TGF-beta receptor related genes in sponge and ancient gene duplications before the parazoan-eumetazoan split.

Members of the transforming growth factor beta (TGF-beta) family mediate key events in cell growth and development. Various receptors for diverse members of the TGF-beta family have recently been isolated and sequenced. These receptors form a family (TbetaR family) with a Ser/Thr kinase domain in common. To understand the divergence pattern of the TbetaR family during animal evolution, we have conducted cloning of cDNAs encoding the TbetaR family members from Ephydatia fluviatilis, a freshwater sponge. We obtained seven cDNAs (sALK-1-sALK-7) which are closely related in structure to known family members. Including these sponge sequences, a phylogenetic tree of the family members was inferred by a maximum likelihood method. The phylogenetic tree suggests that the sponge receptors sALK-1-sALK-3, which are closely related to each other, are sponge homologs of vertebrate activin type I receptor (ActR-I). sALK-5 is likely to be a homolog of TGF-beta type II receptor. sALK-4 and sALK-6 might be ancestral precursors of type I and type II receptors, respectively, and sALK-7 is possibly an ancestral precursor of both types. The tree revealed that most, if not all, of the gene duplications that gave rise to known subtypes with distinct ligand specificities antedate the divergence of parazoans and eumetazoans, the earliest divergence of extant animal phyla.

Animals↗
PubMed1999

Total Ca handling in canine mild Ca overload failing heart.

We analyzed total Ca handling of the left ventricle (LV) in the mildly failing heart preparation induced by a temporary intracoronary Ca overloading intervention in eight excised and cross-circulated canine hearts. This Ca intervention consisted of interruption of coronary blood perfusion by Ca-free oxygenated Tyrode perfusion for 10 min followed by high-Ca (16mmol/l) oxygenated Tyrode perfusion for 5 min. This intervention decreased the LV contractility index, Emax (end-systolic maximum elastance), by 40% after restoration of the blood cross-circulation. We expected a Ca overload or paradox failing heart resembling the postischemic stunned heart and being characterized by an increased O2 cost of Emax. However, LV O2 consumption under mechanically unloading conditions decreased by 30% from control without increasing the O2 cost of Emax. To obtain a mechanistic view of this failing heart, we investigated cardiac total Ca handling by our integrative analysis method. In this method, we obtained the internal Ca recirculation fraction (RF) from the decay beat constant of the postextrasystolic potentiation following each sporadic spontaneous extrasystole in these failing LVs. We combined the RF with the decreased Emax and the unchanged O2 cost of Emax in our recently developed formula of total Ca handling. We found that these failing LVs had a slightly but significantly increased RF accompanied by either a slightly increased futile Ca cycling or a slightly decreased Ca reactivity of Emax, or both. Any of these three possible changes can account for the unchanged O2 cost of Emax. This result indicates that the present mildly failing heart has not yet fallen into a typical Ca overload or paradox by the temporary Ca overloading intervention.

Animals↗
PubMed1999

Myocardial mechanical restitution and potentiation partly underlie alternans decay of postextrasystolic potentiation: simulation.

We have reported that the postextrasystolic potentiation (PESP) decays in alternans or monotonically, respectively, depending on whether the first postextrasystolic beat interval has a compensatory pause or not, in the canine left ventricle. To get better mechanistic insight into the alternans PESP decay, we hypothesized that the myocardial mechanical restitution and potentiation could partly account for both types of PESP decay. To test this hypothesis, we simulated PESP decay on a computer using a documented equation combining myocardial mechanical restitution and potentiation. We changed the first postextrasystolic beat interval after a fixed extrasystolic beat interval without changing regular and other postextrasystolic beat intervals. The simulated PESP decayed in alternans or monotonically as a function only of the first postextrasystolic beat interval. Thus, the myocardial mechanical restitution and potentiation could partly account for both alternans and monotonic decay of PESP. We conclude that myocardial mechanical restitution and potentiation may partly underlie the initial two alternating beats, the first beat being the most potentiated and the second beat being the most depressed, of alternans PESP decay in the canine heart.

Animals↗
PubMed1999

Extensive gene duplication in the early evolution of animals before the parazoan-eumetazoan split demonstrated by G proteins and protein tyrosine kinases from sponge and hydra.

To know whether genes involved in cell-cell communication typical of multicellular animals dramatically increased in concert with the Cambrian explosion, the rapid evolutionary burst in the major groups of animals, and whether these genes exist in the sponge lacking cell cohesiveness and coordination typical of eumetazoans, we have carried out cloning of the G-protein alpha subunit (Galpha) and the protein tyrosine kinase (PTK) cDNAs from Ephydatia fluviatilis (freshwater sponge) and Hydra magnipapillata strain 105 (hydra). We obtained 13 Galpha and 20 PTK cDNAs. Generally animal gene families diverged first by gene duplication (subtype duplication) that gave rise to diverse subtypes with different primary functions, followed by further gene duplication in the same subtype (isoform duplication) that gave rise to isoform genes with virtually identical function. Phylogenetic trees of Galpha and PTK families including cDNAs from sponge and hydra revealed that most of the present-day subtypes had been established in the very early evolution of animals before the parazoan-eumetazoan split, the earliest branching among the extant animal phyla, by extensive subtype duplication: for PTK and Galpha families, 23 and 9 subtype duplications were observed in the early stage before the parazoan-eumetazoan split, respectively, and after that split, only 2 and 1 subtype duplications were found, respectively. After the separation from arthropods, vertebrates underwent frequent isoform duplications before the fish-tetrapod split. Furthermore, rapid amino acid changes appear to have occurred in concert with the extensive subtype duplication and isoform duplication. Thus the pattern of gene diversification during animal evolution might be characterized by bursts of gene duplication interrupted by considerably long periods of silence, instead of proceeding gradually, and there might be no direct link between the Cambrian explosion and the extensive gene duplication that generated diverse functions (subtypes) of these families.

Amino Acid Substitution↗
PubMed1999

Multiple protein tyrosine phosphatases in sponges and explosive gene duplication in the early evolution of animals before the parazoan-eumetazoan split.

Protein tyrosine phosphatases (PTPs) regulate various physiological events in animal cells. They comprise a diverse family which are classified into two categories, receptor type and nonreceptor type. From the domain organization and phylogenetic tree, we have classified known PTPs into 17 subtypes (9 receptor-type and 8 nonreceptor-type PTPs) which are characterized by different organization of functional domain and independent cluster in tree. The receptor type PTPs are thought to be implicated in cell-cell adhesion by association of cell adhesion molecules. Since sponges are the most primitive multicellular animals and are thought to be lacking cell cohesiveness and coordination typical of eumetazoans, cloning and sequencing of PTP cDNAs of Ephydatia fluviatilis (freshwater sponge) have been conducted by RT-PCR to determine whether or not sponges have PTP genes in their genomes. We have isolated nine PTPs, of which five are possibly receptor type. A phylogenetic tree including the sponge PTPs revealed that most of the gene duplications that gave rise to the 17 subtypes had been completed in the very early evolution of animals before the parazoan-eumetazoan split, the earliest branching among extant animal phyla. The family tree also revealed the rapid evolutionary rate of PTP subtypes in the early stage of animal evolution.

Amino Acid Sequence↗
PubMed1999

Protein tyrosine kinase cDNAs from amphioxus, hagfish, and lamprey: isoform duplications around the divergence of cyclostomes and gnathostomes.

Animals evolved a variety of gene families involved in cell-cell communication and developmental control by gene duplication and domain shuffling. Each family is made up of several subtypes or subfamilies with distinct structures and functions, which diverged by gene duplications and domain shufflings before the divergence of parazoans and eumetazoans. Since the separation from protostomes, vertebrates expanded the multiplicity of members (isoforms) in the same subfamily by further gene duplications in their early evolution before the fish-tetrapod split. To know the dates of isoform duplications more closely, we have conducted isolation and sequencing cDNAs encoding the fibroblast growth factor receptor, Eph, src, and platelet-derived growth factor receptor subtypes belonging to the protein tyrosine kinase family from Branchiostoma belcheri, an amphioxus, Eptatretus burgeri, a hagfish, and Lampetra reissneri, a lamprey. From a phylogenetic tree of each subfamily inferred from a maximum likelihood (ML) method, together with a bootstrap analysis based on the ML method, we have shown that the isoform duplications frequently occurred in the early evolution of vertebrates around or just before the divergence of cyclostomes and gnathostomes by gene duplications and possibly chromosomal duplications.

Animals↗
PubMed1999

Monophyly of lampreys and hagfishes supported by nuclear DNA-coded genes.

The phylogenetic position of hagfishes in vertebrate evolution is currently controversial. The 18S and 28S rRNA trees support the monophyly of hagfishes and lampreys. In contrast, the mitochondrial DNAs suggest the close association of lampreys and gnathostomes. To clarify this controversial issue, we have conducted cloning and sequencing of the four nuclear DNA-coded single-copy genes encoding the triose phosphate isomerase, calreticulin, and the largest subunit of RNA polymerase II and III. Based on these proteins, together with the Mn superoxide dismutase for which hagfish and lamprey sequences are available in database, phylogenetic trees have been inferred by the maximum likelihood (ML) method of protein phylogeny. It was shown that all the five proteins prefer the monophyletic tree of cyclostomes, and the total log-likelihood of the five proteins significantly supports the cyclostome monophyly at the level of +/-1 SE. The ML trees of aldolase family comprising three nonallelic isoforms and the complement component group comprising C3, C4, and C5, both of which diverged during vertebrate evolution by gene duplications, also suggest the cyclostome monophyly.

Animals↗
PubMed1999

O(2) cost of contractility but not of mechanical energy increases with temperature in canine left ventricle.

We investigated the effects of myocardial temperature on left ventricular (LV) mechanoenergetics in the excised, cross-circulated canine heart. We used the framework of the LV contractility (E(max))-pressure-volume area (PVA; a measure of total mechanical energy)-myocardial oxygen consumption (VO(2)) relationship. We have shown this framework to be useful to integrative analysis of the mechanoenergetics of a beating heart. In isovolumic contractions at a constant pacing rate, increasing myocardial temperature from 30 to 40 degrees C depressed E(max) and increased the oxygen cost of E(max), which was enhanced by dobutamine, in a linear manner. However, the slope of the VO(2)-PVA relation (reciprocal of contractile efficiency) and its VO(2) intercept remained constant. Q(10) values of E(max), the oxygen cost of E(max), and the oxygen cost of PVA were 0.4, 2.1 and 1.0, respectively, around normothermia. We conclude that the temperature-dependent processes of cross-bridge cycling and Ca(2+) handling integratively depress E(max) and augment its oxygen cost without affecting the oxygen cost of PVA as myocardial temperature increases by 10 degrees C around normothermia.

Animals↗
PubMed1999

Energy expenditure by Ba(2+) contracture in rat ventricular slices derives from cross-bridge cycling.

To clarify the energy-expenditure mechanism during Ba(2+) contracture of mechanically unloaded rat left ventricular (LV) slices, we measured myocardial O(2) consumption (VO(2)) of quiescent slices in Ca(2+)-free Tyrode solution and VO(2) during Ba(2+) contracture by substituting Ca(2+) with Ba(2+). We then investigated the effects of cyclopiazonic acid (CPA) and 2,3-butanedione monoxime (BDM) on the Ba(2+) contracture VO(2). The Ca(2+)-free VO(2) corresponds to that of basal metabolism (2.32 +/- 0.53 ml O(2). min(-1). 100 g LV(-1)). Ba(2+) increased the VO(2) in a dose-dependent manner (from 0.3 to 3.0 mmol/l) from 110 to 150% of basal metabolic VO(2). Blockade of the sarcoplasmic reticulum (SR) Ca(2+) pump by CPA (10 micromol/l) did not at all decrease the Ba(2+)-activated VO(2). BDM (5 mmol/l), which specifically inhibits cross-bridge cycling, reduced the Ba(2+)activated VO(2) almost to basal metabolic VO(2). These energetic results revealed that the Ba(2+)-activated VO(2) was used for the cross-bridge cycling but not for the Ca(2+) handling by the SR Ca(2+) pump.

Animals↗
PubMed1999

Weibull distribution function for cardiac contraction: integrative analysis.

The Weibull distribution is widely used to analyze the cumulative loss of performance, i.e., breakdown, of a complex system in systems engineering. We found for the first time that the difference curve of two Weibull distribution functions almost identically fitted the isovolumically contracting left ventricular (LV) pressure-time curve [P(t)] in all 345 beats (3 beats at each of 5 volumes in 23 canine hearts; r = 0.999953 +/- 0.000027; mean +/- SD). The first derivative of the difference curve also closely fitted the first derivative of the P(t) curve. These results suggest the possibility that the LV isovolumic P(t) curve may be characterized by two counteracting cumulative breakdown systems. Of these, the first breakdown system causes a gradual pressure rise and the second breakdown system causes a gradual pressure fall. This Weibull-function model of the heart seems to give a new systems engineering or integrative physiological view of the logic underlying LV isovolumic pressure generation.

Animals↗
PubMed1999

Analytical expression of effective afterload in aortic and mitral regurgitation.

Effective arterial elastance (Ea) is the coupling parameter between the left ventricle and peripheral circulation in normal subjects. If left ventricular end systolic pressure (Pes), contractility (Es) and Ea are known, left ventricular end diastolic volume (LVEDV) and ejection fraction of the ventricle are completely determined. The aim of this study was to give an analytical expression for Ea in patients with mitral and aortic regurgitation, and predict both LVEDV and the effect of vasodilator therapy on LVEDV. Twenty-three subjects with atypical chest pain, 15 patients with mitral insufficiency and 11 with aortic insufficiency underwent diagnostic cardiac catheterization, coronary angiography, and left ventricular cineangiography, which was analyzed quantitatively. Ea was 2.05 +/- 0.63 in normal subjects, while it was 1.28 +/- 0.71 and 1.57 +/- 0.87 in patients with mitral and aortic insufficiency, respectively. All these groups differed with ANOVA test (p = 0.0031). We tested the ability of the analytical expressions for Ea in normal subjects, and patients with mitral insufficiency or aortic insufficiency to predict measured Ea and LVEDV. Ea and LVEDV were predicted rather accurately in every case (p < 0.0001). We used published data to test the effect of resistance modulation on LVEDV. Predicted and measured LVEDV were linearly correlated both in aortic (p < 0.0001) and mitral insufficiency (p = 0.027). Moreover, in some cases a left ventricular enlargement after vasodilator therapy could be anticipated because of an unbalanced decrease in resistance and heart rate. Ea seems to be the coupling parameter between the left ventricle and the peripheral circulation not only in normal subjects, but also in patients with mitral or aortic regurgitation; its measurement before administering vasodilating drugs may be useful in order to predict the effects on LVEDV, and achieve an optimal ventriculoarterial coupling.

Aortic Valve Insufficiency↗
PubMed1999

Hybrid logistic characterization of isometric twitch force curve of isolated ferret right ventricular papillary muscle.

We previously found that the isovolumic pressure curve of the left ventricle and the isometric twitch force curve of the right ventricular in situ papillary muscle, both of the blood-perfused canine heart, were precisely fitted by our newly proposed hybrid logistic function. This function describes the difference between the two S-shaped logistic functions for the rising and falling components: A/[1+exp{-(4B/A)(t-C)}]-D/[1+exp{-(4E/D)(t-F)}]+G. This function characterizes comprehensively both ventricular and in situ papillary muscle contraction and relaxation. In the present study, we hypothesized that this function could also characterize the force curve of the most popular, standard-type, isolated and Tyrode-superfused papillary muscle preparation. To test this hypothesis, we investigated how precisely the hybrid logistic function could fit 112 isometric twitch force curves observed in eight isolated and Tyrode-superfused ferret right ventricular papillary muscles at different muscle lengths and extracellular Ca2+ concentrations. We always obtained a precise curve fitting with a correlation coefficient above 0.9987. This fitting was much more precise than sinusoidal and polynomial exponential function curve fittings. These results supported the present hypothesis. We conclude that our hybrid logistic function reasonably characterizes the force curve of the isolated myocardial preparation. This result broadens the generality of the hybrid logistic characterization of ventricular isovolumic pressure and myocardial isometric twitch force generation. The hybrid logistic characterization seems to be an integrative expression of contractile processes in myocardial twitch contraction.

Animals↗
PubMed1999

New index for oxygen cost of contractility from curved end-systolic pressure-volume relations in cross-circulated rat hearts.

We have already reported the linear oxygen consumption per beat (VO(2))-systolic pressure-volume area (PVA) relation from the curved left ventricular (LV) end-systolic pressure-volume relation (ESPVR) in the cross-circulated rat heart. The VO(2) intercept (PVA-independent VO(2)) is primarily composed of VO(2) for Ca(2+) handling in excitation-contraction (E-C) coupling and basal metabolism. The aim of the present study was to obtain the oxygen cost of LV contractility that indicates VO(2) for Ca(2+) handling in E-C coupling per unit LV contractility change in the rat heart. Oxygen cost of LV contractility is obtainable as a slope of a linear relation between PVA-independent VO(2) and LV contractility. We obtained a composite VO(2)-PVA relation line at a mid-range LV volume (mLVV) under gradually enhanced LV contractility by stepwise increased Ca(2+) infusion and thus the gradually increased PVA-independent VO(2) values. As a LV contractility index, we could not use E(max) (ESP-V ratio; ESP/ESV) for the linear ESPVR because of the curved ESPVR in the rat LV. A PVA at a mLVV (PVA(mLVV)) has been proposed as a good index for assessing rat LV mechanoenergetics. Since the experimentally obtained PVA(mLVV) was not triangular due to the curved ESPVR, we propose an equivalent ESP-V ratio at a mLVV, (eESP/ESV)(mLVV), as a LV contractility index. This index was calculated as an ESP-V ratio of the specific virtual triangular PVA(mLVV) that is energetically equivalent to the real PVA(mLVV). The present approach enabled us to obtain a linear relation between PVA-independent VO(2) and (eESP/ESV)(mLVV) and the oxygen cost of LV contractility as the slope of this relation.

Animals↗
PubMed1998

Phospholipase C cDNAs from sponge and hydra: antiquity of genes involved in the inositol phospholipid signaling pathway.

To know whether or not the set of genes involved in the inositol phospholipid signaling pathway already existed in the early evolution of animals, we carried out cloning of cDNAs encoding phospholipase Cs (PLCs) from Ephydatia fluviatilis (freshwater sponge) and Hydra magnipapillata strain 105 (hydra). We isolated two PLC cDNAs, PLC-betaS and PLC-gammaS, from sponge and three cDNAs, PLC-betaH1, PLC-betaH2, and PLC-deltaH, from hydra. From the domain organization and the divergence pattern in the PLC family tree, the sponge PLC-betaS and PLC-gammaS and the hydra PLC-deltaH are possibly homologous to the vertebrate PLC-beta, PLC-gamma and PLC-delta subtypes, respectively. A detailed phylogenetic analysis suggests that the hydra PLC-betaH1 and PLC-betaH2 are homologs of the vertebrate PLC-beta1/2/3/Drosophila PLC21 and the vertebrate PLC-beta4/Drosophila norpA, respectively. A phylogenetic analysis of the PLC family and the protein kinase C (PKC) family, together with that of the G protein alpha subunit (Galpha) family, revealed that the origin of the set of genes G(alpha)q, PLC, PKC involved in the inositol phospholipid signaling pathway is very old, going back to dates before the parazoan-eumetazoan split, the earliest branching among extant animal phyla.

Animals↗
PubMed1998

Ancient gene duplication and domain shuffling in the animal cyclic nucleotide phosphodiesterase family.

The animal cyclic nucleotide phosphodiesterases (PDEs) comprise at least seven subtypes, PDE1-7, which differ from each other in domain organization and primary function, and they diverged from an ancestral gene by gene duplication and domain shuffling during animal evolution. To obtain rough estimates for the divergence times of these subtypes, cloning of PDE cDNAs from Ephydatia fluviatilis (freshwater sponge) by RT-PCR was carried out. We obtained four cDNAs, EFPDE1, EFPDE2, EFPDE3, and EFPDE4, which are possibly homologs of the vertebrate PDE1, PDE2, PDE3, and PDE4, respectively, judging from the sequence similarity, domain organization, and branching pattern in the phylogenetic tree. The phylogenetic tree of the PDE family revealed that most gene duplications and domain shufflings that gave rise to different subtypes had been completed in the early evolution of animals before the separation of sponges and eumetazoans.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

Unusual metal ion catalysis in an acyl-transferase ribozyme.

Most studies of the roles of catalytic metal ions in ribozymes have focused on inner-sphere coordination of the divalent metal ions to the substrate or ribozyme. However, divalent metal ions are strongly hydrated in water, and some proteinenzymes, such as Escherichia coli RNase H and exonuclease III, are known to use metal cofactors in their fully hydrated form [Duffy, T. H., and Nowak, T. (1985) Biochemistry 24, 1152-1160; Jou, R., and Cowan, J. A. (1991) J. Am. Chem. Soc. 113, 6685-6686]. It is therefore important to consider the possibility of outer-sphere coordination of catalytic metal ions in ribozymes. We have used an exchange-inert metal complex, cobalt hexaammine, to show that the catalytic metal ion in an acyl-transferase ribozyme acts through outer-sphere coordination. Our studies provide an example of a fully hydrated Mg2+ ion that plays an essential role in ribozyme catalysis. Kinetic studies of wild-type and mutant ribozymes suggest that a pair of tandem G:U wobble base pairs adjacent to the reactive center constitute the metal-binding site. This result is consistent with recent crystallographic studies [Cate, J. H., and Doudna, J. A. (1996) Structure 4, 1221-1229; Cate, J. H., Gooding, A. R., Podell, E., Zhou, K., Golden, B. L., Kundrot, C. E., Cech, T. R., and Doudna, J. A. (1996) Science 273, 1678-1685; Cate, J. H., Hanna, R. L., and Doudna, J. A. (1997) Nat. Struct. Biol. 4, 553-558] showing that tandem wobble base pairs are good binding sites for metal hexaammines. We propose a model in which the catalytic metal ion is bound in the major groove of the tandem wobble base pairs, is precisely positioned by the ribozyme within the active site, and stabilizes the developing oxyanion in the transition state. Our results may have significant implications for understanding the mechanism of protein synthesis [Noller, H. F., Hoffarth, V., and Zimniak, L. (1992) Science 256, 1416-1419].

Acyltransferases↗
PubMed1998

Structural and kinetic characterization of an acyl transferase ribozyme.

We have previously isolated, by in vitro selection, an acyl-transferase ribozyme that is capable of transferring a biotinylated methionyl group from the 3' end of a hexanucleotide substrate to its own 5'-hydroxyl. Comparison of the sequences of a family of evolved derivatives of this ribozyme allowed us to generate a model of the secondary structure of the ribozyme. The predicted secondary structure was extensively tested and confirmed by single-mutant and compensatory double-mutant analyses. The role of the template domain in aligning the acyl-donor oligonucleotide and acyl-acceptor region of the ribozyme was confirmed in a similar manner. The significance of different domains of the ribozyme structure and the importance of two tandem G:U wobble base pairs in the template domain were studied by kinetic characterization of mutant ribozymes. The wobble base pairs contribute to the catalytic rate enhancement, but only in the context of the complete ribozyme; the ribozyme in turn alters the metal binding properties of this site. Competitive inhibition experiments with unacylated substrate oligonucleotide are consistent with the ribozyme acting to stabilize substrate binding to the template, while negative interactions with the aminoacyl portion of the substrate destabilize binding.

Acyltransferases↗