Biomedical subjects
Publications and source records attributed to S Miwa.
We showed that 6R-BH4, a natural cofactor for aromatic amino acids hydroxylases, can stimulate exocytotic DA release independently of its cofactor activity, and ACh release via monoaminergic system. From these results, it is quite likely that 6R-BH4 plays an important role in the regulation of neuronal activity, as a modulator of neurotransmitter release as well as a cofactor for hydroxylases.
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To clarify functional changes of dopaminergic neurons and dopamine (DA) reuptake during and after ischemia, extracellular DA levels in striatum were determined using in vivo brain microdialysis in a 4-vessel occlusion model of male Wistar rats with and without pharmacological interventions. Without interventions, the extracellular DA levels markedly increased during ischemia, but upon reperfusion, rapidly returned to control level. Infusion of tetrodotoxin, a blocker of voltage-dependent Na+ channels, was without effect on the DA surge during ischemia, but decreased the DA levels after reperfusion to the same extent as in control rats. Pretreatment with nomifensine, an inhibitor of DA reuptake, was also without effect on the surge, but reduced the rate of DA decline after reperfusion to one-fifth of the rate without the pretreatment. When nomifensine was administered 40 min after reperfusion, extracellular DA levels increased to the same extent as in control rats. Infusion of high K+ 1 h after reperfusion induced a smaller increase in extracellular DA levels than that in control rats. It took 96 h for this reduced response to high K+ stimulation to recover after reperfusion. These results suggest that the DA surge during ischemia is mainly derived from action potential-independent DA release (means dysfunction of dopaminergic neurons), although activity of DA reuptake is completely inhibited. After reperfusion, the basal function of dopaminergic neurons and activity of DA reuptake rapidly recover, but the neurons are functionally disturbed to release less DA in response to a given stimulus for several days.
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cDNA clones for human R-type pyruvate kinase (PK) were isolated from a human reticulocyte cDNA library, constructed by PCR with a single gene-specific primer. The full-length cDNA was 2060 base pairs long, and the cDNA encoded 574 amino acids, the same number as that by rat R-type PK. Compared with human L-type PK, R-type PK was 31 amino acids longer at the amino terminus. We also cloned and characterized R-type PK cDNA clones from patients with hereditary hemolytic anemia from a PK deficiency, PK Tokyo. A single nucleotide substitution (ACG to ATG) was found at nucleotide 1151 of the coding sequence of the R-type PK, which caused an amino acid substitution, Thr384----Met. Dot blot hybridization of PCR-amplified genomic DNA from patients and their parents by allele-specific oligonucleotide probes showed that the parents, who were second cousins, were heterozygous. To confirm that the nucleotide change was responsible for the variant phenotype, we expressed the L-type PK with the single amino acid change in Escherichia coli and characterized the enzyme. The variant PK was thermolabile and moved slowly in the polyacrylamide gel buffered in 10 mM Tris.HCl, pH 8.3; these characteristics were fully compatible with data obtained from the patient's PK. From these results, we concluded that enzymatic stability of the variant was affected by the point mutation of the PK-encoding gene.
Recently, we have reported that 6R-L-erythro-tetrahydrobiopterin (6R-BH4), a natural cofactor for hydroxylases of phenylalanine, tyrosine and tryptophan, has a dopamine releasing action in the rat striatum independent of its cofactor role. Here we studied the effects of 6R-BH4 on acetylcholine (ACh) release in the rat hippocampus using brain microdialysis. Intracerebroventricular injection of 6R-BH4 dose-dependently increased extracellular ACh levels monitored by brain microdialysis. Biopterin, an oxidized form of 6R-BH4, and 6S-BH4, an unnatural diastereoisomer of 6R-BH4, had little effect on the ACh levels. The 6R-BH4-induced increase in ACh levels was eliminated after inhibition of voltage-dependent Na+ channels by tetrodotoxin, but not after depletion of catecholamines by reserpine. These results show that 6R-BH4 has direct ACh releasing action in vivo.
Morphological and biochemical changes in the muscular tissue of metamorphosing flounder were studied in relation to the regulatory role of thyroid hormone. Premetamorphic larvae were reared in seawater alone or seawater containing either thyroxine (T4) or an antithyroid drug (thiourea, TU). Histological changes in the muscle were examined and biochemical changes in the muscle proteins were evaluated by SDS-PAGE and immunoblotting for troponin T (TNT). The muscle tissue of premetamorphic larvae was characterized by abundant vacuoles and basophilic sarcoplasm. In control fish, the larval muscle transformed into the adult type during metamorphic climax; the fibers were filled with abundant myofibrils and the vacuoles disappeared. Analysis by SDS-PAGE showed that the bands at 41.5, 35.5, 34.0, 33.5, 25.5, 23.0, 20.0, and 19.0 kDa clearly increased in density from the climax stage. Premetamorphic larvae possessed two immunoreactive TNT isoforms of 41.5 and 34.0 kDa, the former being predominant. At the climax stage an additional isoform appeared at 33.5 kDa, and the 34.0- and 33.5-kDa TNT became predominant. The administration of T4 precociously induced these histological and biochemical changes in the muscle tissue of flounder larvae. In contrast, TU treatment inhibited these developmental changes in the larval muscle. Our results suggest that the developmental changes in the muscular tissue of metamorphosing flounder are regulated by thyroid hormone.
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The purpose of the present study is to clarify the effects of hypoxia on the activity of the dopaminergic neurons in the brain and its mechanism of action. For this purpose, the effects of hypoxia on the extracellular levels of 3,4-dihydroxyphenylethylamine (dopamine) were examined in the rat striatum using in vivo brain microdialysis in the presence or absence of pretreatment with either tetrodotoxin (a blocker of voltage-dependent sodium channels) or nomifensine (a blocker of dopamine reuptake). Exposure to various degrees of hypoxia (15, 10, and 8% O2 in N2) increased dopamine levels in striatal dialysates to 200, 400, and 1,100%, respectively, of the control value. On reoxygenation, dopamine levels in the dialysates rapidly returned to the control level. Reexposure to hypoxia increased the dopamine levels to the same extent as during the first exposure. After addition of tetrodotoxin (40 microM) to the perfusion fluid or pretreatment with nomifensine (100 mg/kg, i.p.), exposure to hypoxia no longer increased the dopamine levels. These results suggest that although hypoxia induces an increase in the extracellular dopamine levels (hence, an apparent increase in the activity of the dopaminergic neurons), this increase is not the result of an increase in dopamine release itself, but rather the result of inhibition of the dopamine reuptake mechanism.
1. To characterize NKY-722, a novel hydrophilic dihydropyridine derivative, as a Ca2+ antagonist, we examined its effects on 45Ca2+ influx, intracellular free Ca2+ concentrations [( Ca2+]i), and release of noradrenaline and adrenaline in bovine cultured adrenal chromaffin cells. 2. NKY-722 had little effect on basal 45Ca2+ influx into the resting cells, but inhibited high K+ (35.9 mM)-evoked 45Ca2+ influx in a concentration-dependent manner with an IC50 value of 5.2 nM. 3. NKY-722 inhibited high K(+)-evoked increases in [Ca2+]i in a concentration-dependent manner without effect on the resting [Ca2+]i. 4. NKY-722 had little effect on basal release of noradrenaline and adrenaline but inhibited high K(+)-evoked release of noradrenaline and adrenaline in a concentration-dependent manner with IC50 values of 5.0 nM and 4.8 nM, respectively. 5. Nicardipine, a prototype of NKY-722, also inhibited high K(+)-evoked 45Ca2+ influx and release of noradrenaline and adrenaline in a concentration-dependent manner: the IC50 value for high K(+)-evoked 45Ca2+ influx was 51 nM, and the values for high K(+)-evoked release of noradrenaline and adrenaline were 52 nM and 50 nM, respectively. 6. These results show that NKY-722 is a hydrophilic Ca2+ antagonist ten times more potent than nicardipine.
We raised antibodies to brain fodrin and erythrocyte ankyrin and examined the distribution of the antigens in cultured bovine chromaffin cells by immunocytochemical techniques. Immunofluorescence microscopy of whole cells showed intense labeling for both proteins, but fine localization could not be determined. In contrast, in cell specimens mechanically unroofed before fixation, the distribution of the two proteins revealed an apparent difference in the ventral plasma membrane: immunofluorescence for fodrin was dense and mostly even, whereas that for ankyrin appeared as scattered dots. Immunogold electron microscopy of the unroofed cells showed that labeling for fodrin was localized in a network of thin filaments, the diameter of which was 2-3 nm at the thinnest portion. Ankyrin labeling was mostly associated with filaments 5-10 nm in diameter. Notably, labeling for both fodrin and ankyrin was found over the coated membrane. The present results indicate that fodrin and ankyrin in the chromaffin cell do not constitute a submembranous network as spectrin and ankyrin do in the erythrocyte; whereas fodrin is closely associated with the plasma membrane, ankyrin is mostly linked to the cytoskeleton. The existence of both proteins in the coated region implies that they are functionally related to exocytosis and/or to ensuing membrane retrieval in the chromaffin cell.
To assess the influence of autonomic regulation on automaticity in patients with intrinsic sinus node dysfunction, heart rate responses to autonomic drugs were evaluated in 28 patients with sick sinus syndrome and in 8 normal subjects. Heart rates before and after intravenous administration of isoproterenol (Isp), propranolol, atropine, and methoxamine were measured. To compare the results with electrophysiologic data, heart rate and automaticity recovery time (ART) before and after pharmacologic autonomic blockade (AB) were evaluated. Seventeen patients without syncope showed a similar heart rate response after administration of Isp to that of normal subjects, but 11 patients with syncope showed a significantly lower response than patients without syncope. Responses to atropine and methoxamine were lower and response to propranolol was larger in patients as compared to normal subjects. However, no significant difference was observed between patients with and without syncope. Twelve patients showed severely prolonged max ART exceeding 5000 msec after AB. Seven of them showed preserved response to Isp and max ART before AB was significantly shorter than that after AB. The other 5 patients with lower response to Isp showed no significant change in max ART before and after AB. In conclusion, sympathetic regulation in patients with preserved response to Isp might compensate for the impaired intrinsic automaticity in preventing syncope even in patients with severely impaired intrinsic sinus node function.
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The amount of polyamines in urine from patients with various neoplasms is larger than in normal subjects. We have determined the concentration of 5'-methylthioadenosine (MTA), a by-product of the polyamine biosynthesis, in patients with malignancies as well as normal subjects. Our studies indicate that the amount of MTA in urine from patients with leukemias and malignant lymphomas was higher than in normal subjects (p less than 0.005). Urine samples from patients with other malignancies contained normal amounts of MTA. The levels of blood MTA in patients with leukemias before treatment or in relapse was higher than in control subjects (p less than 0.005), while in patients with other malignancies and leukemia in remission, the levels were not different from control subjects. Peripheral blood MTA levels clearly decreased after effective chemotherapy. The measurement of MTA levels in urine and blood may not be as useful as polyamine assays for the detection of malignancies, but blood levels of MTA may be useful as an indicator of the efficacy of chemotherapy in leukemic patients.
A 44-year-old previously healthy male was diagnosed as anemic and treated at a nearby hospital. A year later, he was admitted to our hospital for precise examination of the progression of refractory anemia. Blood examination showed hemolytic anemia and more detailed examination of this hemolysis revealed pyruvate kinase deficiency. The activity was 15.1% of a normal control. Pyruvate kinase activities of his family members were normal or slightly decreased. Ten months after admission to our hospital, 2% of blast cells with Auer's body in the peripheral blood were noted which increased progressively. The bone marrow contained 17.3% of blast cells with a subsequent diagnosis of acute myelogenous leukemia being made. Although intensive chemotherapy was performed, the patient achieved a brief remission and died 2 years after admission to our hospital.
During the relatively recent period in which normal genes for most red cell enzymes have been isolated, the techniques of molecular biology have been applied to the studies of erythroenzymopathy. Single nucleotide substitutions have been identified in aldolase, triosephosphate isomerase, glucose 6-phosphate dehydrogenase, and adenylate kinase variants by the cloning and nucleotide sequence of the patients' genes. Up to now, all of the enzyme-deficient variants which have been investigated have been caused by point mutations. An exception is a hemolytic anemia secondary to increased adenosine deaminase (ADA) activity. Red cell ADA activity increases on the order of a hundred-fold in affected individuals. The basic abnormality appears to result from overproduction of structurally normal enzyme due to abnormal transcriptional or translational efficiency.
Pyruvate kinase (PK) deficiency was initially described by Valentine et al. in 1961. Since then, more than 300 cases have been described, including 65 in Japan. PK deficiency is the most common hereditary nonspherocytic hemolytic anemia among several red cell enzyme defects of the Embden-Meyerhof glycolytic pathway. The clinical manifestations are highly variable. Splenectomy usually increases the hemoglobin level by about 2 g/100 mL. Standardization of methods for characterization of PK variants was achieved in 1979. There are four PK isozymes, M1, M2, L and R, in mammalian tissues. We have clarified the switch from M2-type to L-type PK during maturation of erythroid precursor cells. Recently we cloned and sequenced a full length human L-type PK cDNA. It will be useful to clarify the molecular basis of PK deficiency.
To better characterize the role of serotonin in the Arthus reaction, we examined the concentration of the amine and the activities of serotonin-metabolizing enzymes, monoamine oxidase (MAO) and serotonin-N-acetyltransferase (NAT), in reaction sites induced in guinea pig skin. The specific activity of total MAO in the intact skin was 108.0 +/- 15.9 pmol/min/mg protein, and consisted of about 92% of type A activity and 8% of type B. The activity of total MAO was about 10 times greater than that of NAT. Total MAO activity increased to 130%-150% of control levels at 2 h after initiation of the reaction and approximated the control level at 3 to 6 h. Subsequently, the activity decreased linearly to 50% at 12 h and to 20% at 24 h. Although the time-dependent changes of MAO type A activity were similar to those of total MAO activity, MAO type B activity increased to 42% at 30 min, remained at 30%-40% until 6 h, and then decreased to 20% at 12 h and to 5% at 24 h. NAT activity in the reaction sites decreased with time to 50% of the control at 30 min and to 35% at 4 h and was stationary until 24 h. The serotonin concentration decreased linearly with time to 16% of the control level at 1 h, increased sharply to 240% at 6 h, and remained at more than 200% until 24 h. This biphasic change in serotonin concentration seems to be related to the dynamic changes in the activities of serotonin-degrading enzymes. In addition, the accumulation of platelets in the reaction sites may increase serotonin concentration and MAO activity subsequent to 1 h after the initiation.