Biomedical subjects

S Imai

Publications and source records attributed to S Imai.

At least 397 records · Page 22Linked to original sources

PubMed1991

A novel protein induced in cortical epileptic focus of rat cerebrum: a possible linkage to epileptogenesis.

To precisely evaluate a protein-related mechanism of epileptogenesis, we quantitatively analyzed the 70-kDa protein (namely, P70), a specific protein found in the cobalt-induced epileptic focus, and examined its effect on the electrocorticogram (ECoG) and cortical neurons in cerebral slices and its immunocytochemical localization in rats. Cobalt-induced cortical epileptogenic cortex exhibited a marked induction of P70. Its initiation time was ahead of the generation of epileptogenic activities. The anticonvulsant phenytoin (PHT) attenuated the cobalt-induced epileptogenic activities, but failed to suppress protein induction. Injection of this protein into the motor region of normal rat cerebral cortex elicited an epileptic ECoG and behavioral seizures. It also caused epileptiform activity with paroxysmal depolarization shifts in cortical neurons. These epileptogenic phenomena elicited by P70 were abolished by prior treatment with PHT or phenobarbital. Immunocytochemical analysis with an antiserum against P70 revealed that the reactivity was confined to pyramidal cells only in the region of the focus and was mainly localized on somatic, dendritic, and nuclear membranes and microtubles. These findings suggest that P70 may be linked to epileptogenesis.

Animals↗

PubMed1991

Na+/H+ exchange is not operative under low-flow ischemic conditions.

Using 31P-NMR the existence of Na+/H+ exchange system and its contribution to intracellular pH (pHi) regulation were examined in the isolated isovolumic rat heart under physiological and pathophysiological conditions. Ethylisopropylamiloride (EIPA) was used as a tool to search into the role of Na+/H+ exchange system. In the normal well-oxygenated heart dose-dependent negative chronotropic effects were observed with 10(-6) to 10(-5) M EIPA. After 10(-4) M the heart ceased to beat and a progressive fall of high energy phosphates compounds occurred. However, contrary to expectation pHi did not fall but rose after EIPA. In NH4Cl-loaded hearts removal of NH4Cl resulted in a fall of the pHi followed by a rapid recovery to the normal pHi. After 10(-5) M EIPA the fall of pHi became greater and there was no recovery within 35 min of observation period. This dose of EIPA, however, did not affect the time course of changes in the pHi during 60 min of low-flow ischemia (0.2 ml/min). It is concluded that pHi regulation following an acute acid loading is dependent on amiloride-sensitive Na+/H+ exchange. However, Na+/H+ exchange system does not play an important role in maintenance of the pHi under normoxic or ischemic condition. In the normoxic heart EIPA produced a decrease in heart rate without producing any change either in myocardial energy metabolism or in pHi. Thus, the compound could be categorized as a bradycardic agent.

Amiloride↗

PubMed1991

Activation process of calcium-dependent potassium channel in Euhadra neurons: involvement of calcium/calmodulin and subsequent protein phosphorylation.

1. The activation process of Ca(2+)-dependent potassium channel was studied electrophysiologically and pharmacologically using identified neurons of the land snail, Euhadra peliomphala. 2. Ca(2+)-mediated delayed outward K current (IKD) was dose-dependently reduced by the calmodulin inhibitors, N-(6-aminohexyl)-1-naphthalenesulfonamide (W-5, week) and N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide (W-7, potent). These antagonists also caused a slight membrane depolarization and increase in impulse discharge frequency with decrease in the amplitude of both action potential and after hyperpolarization. 3. The cAMP-dependent protein kinase inhibitor N-[2-(methylamino) ethyl]-5-isoquinoline-sulfonamide (H-8) did not produce any significant effect on IKD and membrane potential. 4. Calmodulin, when injected into the neuron which had been treated with either W-5 or W-7, transiently restored the suppressed IKD nearly to the pretreatment level, and caused hyperpolarization of the cell. In contrast, calcium chloride, intracellularly injected in the same way, had little effect on both the IKD and the membrane potential shifted by these antagonists. 5. Intracellular injection of kinase II, a Ca2+/calmodulin-dependent protein kinase, caused an increase in the IKD and membrane hyperpolarization. Similar but weak effects were produced when a catalytic subunit (CS) of cAMP-dependent protein kinase was intracellularly injected. However, the neurons pretreated with W-7 no longer had any detectable increase in the IKD and hyperpolarization of the membrane. 6. These results suggest the possibility that Ca2+/camodulin-dependent protein phosphorylation may finally mediate the activation of a certain number of potassium channels.

Animals↗

PubMed1991

Monoclonal antibodies against CA125-bearing antigenic molecule fragments; reactivity with mucinous ovarian tumours and lung cancers.

We first established a cell strain, SHIN-3, from human ovarian serous cystadenocarcinoma, and performed antigen analysis for CA125 which appeared to be massively secreted by the SHIN-3 cells. Protein digestion analysis revealed that a low molecular weight peptide of 49 kDa showed antigen activity. In the present study, we describe a mouse monoclonal antibody against this low molecular peptide, presumed to be part of the CA125-bearing antigenic molecule. Purified antigen prepared from culture supernatant was adsorbed to nitrocellulose membranes and injected intrasplenically in mice. Of the obtained 398 clones, 10 clones were selected by screening in an ELISA test. Of the 10, two were further selected, i.e. SH-9. This hybridoma produces IgG1 monoclonal antibodies. Immunoblotting analysis revealed that SH-9 recognizes the low molecular peptide used as the immunogen. Immunohistological examination with the SH-9 MAb revealed that the antigen reacted with the bronchial epithelium, cervical glands of the uterus and other various normal tissues. Of tumorous tissues, the antibody mainly reacted with ovarian tumours, but positive reactions were also observed with pulmonary adenocarcinomas or squamous cell carcinomas. Surprisingly the positive rate was high in mucinous tumour of the ovary, while no positive reaction was observed in serous tumours. Dot-blot assay using SH-9 revealed that 17/19 (90%) sera of lung cancer patients were positive for the titre suggesting that SH-9 may be useful to set up a serum test for lung cancers.

Animals↗

PubMed1991

Protein changes associated with cobalt-induced epileptic activity in rat cerebral cortex.

In cobalt-induced epileptogenic cortex in rats, a marked increase in two proteins of about 84 kDa and 70 kDa, a slight increase in 12-kDa and 10-kDa proteins and a decrease in a protein of about 57 kDa were noted, as determined by SDS-polyacrylamide gel electrophoresis. The initiation of these protein changes was ahead of the generation of epileptogenic activities. The anticonvulsant drugs phenytoin (PHT) and phenobarbital (PB) attenuated the cobalt-induced epileptogenic activities, but failed to suppress the protein changes. Among these proteins, a 70-kDa protein, when injected intracortically into the motor region of the normal rat cerebrum, evoked epileptic discharges on the electrocorticograph and behavioral seizure, which were abolished by prior treatment with PHT or PB. These findings suggest that the above protein changes are not an indirect offshoot of secondary stimulation of neurons by neurotransmitters or neuromodulators, and that P70 may contribute to the generation of epileptic seizure activities.

Animals↗

PubMed1991

Purification and characterization of a new GTP-binding protein of Mr 24,000 in bovine brain membranes.

A GTP-binding protein with an Mr of 24,000 was purified from a cholate extract of bovine brain membranes in addition to the previously reported alpha beta gamma-trimeric GTP-binding proteins (G proteins). Partial amino acid sequence analysis of the purified 24-kDa protein revealed that it was not identical to any of the low Mr GTP-binding proteins already reported, but similar to the rac-gene products serving as the substrate of an ADP-ribosyltransferase (C3) purified from the culture medium of Clostridium botulinum type C. However, the 24-kDa protein was not ADP-ribosylated by the botulinum C3 enzyme. The 24-kDa protein was purified as a nucleotide-free form and characterized by the following unique properties distinct from those of alpha beta gamma-trimeric G proteins. (1) Mg2+ was essentially required for nucleotide binding to the 24-kDa protein; there was a progressive increase in its binding affinity for nucleotides as the concentration of the divalent cation was increased. (2) Nucleotides previously bound to the 24-kDa protein were rapidly dissociated from the protein in Mg(2+)-free medium, in accord with the fact that the protein was indeed purified as a nucleotide-free form with Mg(2+)-free solutions. (3) The 24-kDa protein apparently exhibited much lower GTPase activity than do alpha beta gamma-trimeric G proteins because the product GDP was released from the 24-kDa protein in exchange for the substrate GTP only at a very low rate. Based on these findings, a possible role of the 24-kDa protein in cellular signalling is discussed in comparison with well characterized alpha beta gamma-trimeric G proteins.

ADP Ribose Transferases↗

PubMed1991

The bialaphos biosynthetic genes of Streptomyces viridochromogenes: cloning, heterospecific expression, and comparison with the genes of Streptomyces hygroscopicus.

The bialaphos resistance gene, bar, was used as a selectable marker to isolate the bialaphos production genes (bap) from the Streptomyces viridochromogenes genome. The S. viridochromogenes bar gene was cloned on overlapping restriction fragments using pIJ680 and pIJ702 in the bialaphos-sensitive host, S. lividans. Although the restriction endonuclease cleavage map of these fragments was not similar to the bap cluster of S. hygroscopicus, the presence and location of bar and four other bap genes as well as a gene required for the transcriptional activation of the cluster (brpA) was demonstrated by heterologous cloning experiments using a series of previously characterized bialaphos-nonproducing S. hygroscopicus mutants. Since recombination-deficient mutants of streptomycetes have not been isolated, restored function provided by cloned homologous DNA results from both recombination (marker rescue) and complementation in trans. In contrast to our previously reported homologous cloning experiments where we were able to define the position of mutant alleles by recombination, in these heterologous cloning experiments we observed little if any recombination between plasmid-cloned genes and the chromosome. As a result, this approach allowed us to define the location and orientation of functional genes using a genetic complementation test. The organization of the clustered S. viridochromogenes bap genes was indistinguishable from the corresponding S. hygroscopicus mutant alleles. The fact that the S. viridochromogenes transcriptional regulatory gene, brpA, functioned in S. hygroscopicus implied that some transcriptional regulatory signals may also be interchangeable. In these two Streptomyces species, which have considerable nucleotide sequence divergence, the complex biochemical and genetic organization of the bialaphos biosynthetic pathway is conserved.

Anti-Bacterial Agents↗

PubMed1991

Low uracil concentration in the liver might be responsible for the decreased antineoplastic activity of fluoropyrimidines in mice with CCl4-induced chronic liver dysfunction.

Some fluoropyrimidines are considered to be metabolized in liver microsomes. The present study was designed to assess the effect of chronic liver dysfunction on the antineoplastic activity of fluoropyrimidines. Chronic liver dysfunction was induced in BALB/c mice by 8 weeks of CCl4 injections. The 5-fluorouracil (5-FU)-sensitive MOPC-104E and 5-FU-resistant Meth-A cells were inoculated subcutaneously into the mice and then various fluoropyrimidines were administered intragastrically. The antitumor activity of the fluoropyrimidines decreased in mice with chronic liver dysfunction, although the concentration of 5-FU in the tumor of normal mice did not differ from that of mice with liver dysfunction. However, the concentration of uracil in the liver was decreased in mice with chronic liver dysfunction. On the other hand, the percent conversion of Tegafur [1-(2-tetrahydrofuryl)-5-FU] to 5-FU in the normal liver did not differ from that in the dysfunctional liver. These results suggest that low uracil concentrations in the liver may result from chronic liver dysfunction and lead to decreased antitumor efficacy of fluoropyrimidines.

Animals↗

PubMed1991

[Studies on plasmalemmal Ca(2+)-pump ATPase--for a better understanding of the mechanisms of relaxation of smooth muscle].

First, we will briefly describe how our study on the mechanisms of relaxant effects of nitroglycerin and related compounds (NG) on the vascular smooth muscle developed to a study on the sarcolemmal (SL) Ca(2+)-ATPase. These compounds were found to have no effects on the voltage-dependent Ca2+ channel and Ca(2+)-induced Ca2+ release from the sarcoplasmic reticulum (SR) and Na(+)-Ca2+ exchange mechanism has been shown not to play an important role in the vascular smooth muscle. Furthermore, when we initiated our study, the idea of receptor-operated Ca2+ channels and Ca2+ release from the SR by inositol triphosphates were not known. A major part of this review is devoted to a description of the characteristic features of SL Ca(2+)-ATPase and its regulation by various protein kinases. References to SR enzyme are made when necessary. Brief mention is made of the putative molecular structure and its possible variations as envisaged by genetic engineering techniques. However, particular attention is directed to the regulation by cyclic GMP-dependent protein kinase as this seems to be most important as regards the mechanisms of vascular smooth muscle relaxation by NG.

Animals↗

PubMed1991

Effect of carvedilol on venous return: a mechanism of reduction in blood pressure.

We studied the effect of carvedilol, a beta-blocker with a potent alpha-blocking activity, on venous return in anesthetized dogs. Though 3 micrograms/kg of carvedilol caused a slight increase in blood pressure and total peripheral resistance, these changes disappeared by further doses of the agent. On the other hand, each dose of carvedilol (3-100 micrograms/kg) decreased venous return significantly and dose-dependently. These results indicate that the hypotensive effect of carvedilol mainly depends on the decrease in venous return rather than arterial vasodilation.

Adrenergic beta-Antagonists↗

PubMed1991

Hemodynamic effects of benazeprilat in the anesthetized dog with acute left ventricular failure.

To examine the hemodynamic effects of benazepril, an angiotensin converting enzyme inhibitor, in left ventricular failure, its active metabolite benazeprilat was administered during acute ischemic left ventricular failure in anesthetized open chest dog induced by repeated injections of plastic microspheres into the left coronary artery. The coronary embolization with microspheres resulted in a moderate and stable left ventricular pump failure characterized by increased left ventricular end-diastolic pressure (LVEDP) and decreased cardiac output (CO). Benazeprilat (30 micrograms/kg) administered intravenously after a stabilization period lowered LVEDP and maintained CO. The total peripheral resistance was reduced with benazeprilat. The oxygen consumption and the coronary blood flow were reduced with benazeprilat because of a decrease in wall tension and afterload. These results suggest that benazeprilat (benazepril) has beneficial effects for the treatment of acute left ventricular failure.

Acute Disease↗

PubMed1991

Incomplete proviral genome of mouse mammary tumour virus is present on chromosome Y of NIH Swiss and some genetically related mouse strains.

An incomplete proviral genome of endogenous mammary tumour virus (MMTV) was found in DNA of several strains of mice. This MMTV-related sequence was assigned to the Y chromosome since it was clearly observed in male mice only. This MMTV provirus contained a sequence related to LTR (long terminal repeat), but not to gag-pol and env genes. NFS, NIH Swiss/S, STS/A, and DD/Tbr mice have this sequence but BALB/cHeA, SHN, SLN, C57BL/6NJcl, C3H/HeNJcl and CBA/JJcl mice are negative. In the strains containing this sequence, a DNA test for the sequence makes it possible to easily distinguish the DNAs of male or female mice.

Animals↗

PubMed1991

Strain difference in the susceptibility of thymocytes to radiation-induced apoptosis: in vitro study.

The susceptibility of thymocytes from STS/A to radiation-induced cell death was compared with that of thymocytes from BALB/cHeA. After in vitro exposure to 12 Gy X-ray, thymocytes were incubated at 37 degrees C for 8 h and then cell mortality was assessed by 0.02% erythrosin B exclusion. Cell death took place from 2 h in the incubation period, reaching a maximum at 6 h for both strains. The dose-effect on cell death at 4 h of incubation was examined after 1-24 Gy of X-irradiation. An increase in cell death was detectable even at 1 Gy in both strains. The number of dead cells in BALB/cHeA gradually increased with doses of more than 1 Gy, finally to a maximum (approximately 60%) in the dose range of 8-12 Gy, whereas the maximum cell death in STS/A was approximately 40%. The difference between the strains at maximum cell death was significant (P less than 0.005). The difference in the radiosensitivity of thymocytes between the two strains could not be attributed to a difference in the composition of their subpopulations because flow cytometric analysis based on the expression of CD4 and CD8 showed no intrinsic difference in the thymocyte subpopulations of BALB/cHeA and STS/A.

Animals↗

PubMed1991

Effects of lidocaine on ischemic myocardial metabolism assessed by 31P-NMR in the isolated perfused rat heart.

Using an isolated perfused rat heart preparation, the protective effects of lidocaine and diltiazem on ischemic derangements of myocardial energy metabolism were studied with 31P-nuclear magnetic resonance spectroscopy. The hearts were perfused with a solution containing lidocaine (4.27 x 10(-5), 12.80 x 10(-5) M) or diltiazem (2.22 x 10(-7), 2.22 x 10(-6) M) for 15 min prior to the induction of global ischemia. The decrease in myocardial oxygen consumption rate, assessed as the product of heart rate and left ventricular systolic pressure (HR x LVP), was greater in diltiazem-treated than in lidocaine-treated hearts. Diltiazem and lidocaine significantly retarded the fall in myocardial pH during ischemia and improved ATP recovery after reperfusion. There was a good correlation between suppression of HR x LVP observed before induction of ischemia and decreased drop in pH during the early phase of ischemia in the diltiazem-treated groups (r = -0.78, p less than 0.01), but not in the lidocaine-treated groups. These results indicate that the beneficial effects of diltiazem on the ischemic myocardium are due primarily to the cardio-depressant effects. The beneficial effects of lidocaine cannot, however, be explained solely on the basis of the depression of oxygen consumption.

Animals↗

PubMed1991

[Highly metastatic mammary tumors in M. m. musculus Sub-Jyg (JYG mouse)].

The present paper reports the highly metastasis of mammary tumors in Chinese wild mouse M. m. musculus Sub-Jyg (JYG mouse), which was recently inbred at the National Institute of Genetics, Mishima, Japan. The incidence of mammary tumors at 18th generation was 89% at about 9 months of age. Histology of mammary tumors in 19 cases examined were medullary or papillary adenocarcinoma (Comedo type) with highly anaplastic features. Metastasis was found not only in the lungs (53%), but also in the liver (21%) and spleen (16%), respectively. MMTV antigen and particle were also found in various organs by immunoperoxidase method and electronmicroscopy. As a result of present observation, JYG mouse was considered to be a unique model in the study of the metastasis of mammary tumors to the liver and spleen.

Adenocarcinoma, Papillary↗

PubMed1991

The different activation of int genes in mammary carcinomas developed in three mouse strains harboring mouse mammary tumor viruses derived from DD/Tbr.

RNA expressions of common integration site (int) genes and several oncogenes were investigated in mammary carcinomas spontaneously developed in different three strains of mice; DD/Tbr, NIH Swiss and BALB/c which harbor DD-MMTV derived from DD/Tbr mouse. Latter two strains of mice were designated NIH/Mtv+ and BALB/Mtv+, respectively. An increased expression of int-1 (wnt-1) and int-2 genes was observed in 56% (9/16) and 50% (8/16) of mammary carcinomas of DD/Tbr mice, respectively. Either int-1 or int-2 RNAs were expressed in 81% (13/16) of the carcinomas of DD/Tbr mice. IN NIH/Mtv+ mice, activation of int-1 and int-2 was observed in 41% (7/17) and 24% (4/17) of mammary carcinomas, respectively. Either int-1 or int-2 RNAs were expressed in 47% (8/17) of the carcinomas examined in this strain. In BALB/Mtv+ mice, on the other hand, either int-1 or int-2 gene were transcribed into RNAs at low frequency (33%: 3/9). These results suggest that the frequency of activation of int genes in mammary carcinomas induced by the same DD-MMTV in three strains of mice is genetically defined characteristics of these strains, and that the involvement of int-1 and int-2 genes in virus-induced mammary carcinogenesis may be influenced by genetic properties of animals. The activation of int-1 and int-2 genes did not clearly correlate with an increase in the expression of oncogenes examined; H-ras, K-ras, N-ras, myc, raf, fgr, fms, erB, mos, and src genes.

Animals↗

PubMed1991

Successful use of the centrifugal ventricular assist device for postcardiotomy cardiogenic shock.

A centrifugal pump was successfully used as a left ventricular assist device (LVAD) in a 54-year-old female who developed cardiogenic shock following open heart surgery. Cardiac index prior to the LVAD support was 1.4 l/min/m2 and increased to 3.0 l/min/m2 at removal of the device, which assisted for 88h. She resumed her daily activity 10 months after the operation and is in New York Heart Association functional class I.

Cardiac Surgical Procedures↗

PubMed1991

Conversion of bialaphos to other oligopeptides containing phosphinothricin by Streptomyces hygroscopicus.

Two oligopeptides containing phosphinothricin were accumulated in the culture of bialaphos (BA) producer Streptomyces hygroscopicus SF1293 when large amount of BA was added to the culture at idio phase. One of the oligopeptides was a new substance, BA dimer (phosphinothricyl-alanyl-alanyl-phosphinothricyl-alanyl-alan ine), and the other was a known substance called If (phosphinothricyl-alanyl-alanyl-phosphinothricin). Though BA none producing mutants which were blocked at the steps 1, 10 and 13, respectively in BA biosynthesis also converted BA to BA dimer and If, the mutants blocked at the step 11 (alanylation) could not curry out the conversion. Antibiotic activities of BA dimer and If were lower than 1/100 of BA.

Aminobutyrates↗