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Biomedical subjects

G Matsumoto

Publications and source records attributed to G Matsumoto.

At least 19 recordsLinked to original sources
PubMed1992

Proposed tertiary structure of the sodium channel.

On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. 186, 1), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with that of Noda et al. (Nature 320; 188-192, 1986).

Amino Acid Sequence↗
PubMed1992

Primary structure of squid sodium channel deduced from the complementary DNA sequence.

The complete amino acid sequence of a sodium channel from squid Loligo bleekeri has been deduced by cloning and sequence analysis of the complementary DNA. The deduced sequence revealed an organization virtually identical to the vertebrate sodium channel proteins; four homologous domains containing all six membrane-spanning structures are repeated in tandem with connecting linkers of various sizes. A unique feature of the squid Na channel is the 1,522 residue sequence, approximately three fourths of those of the rat sodium channels I, II and III.

Amino Acid Sequence↗
PubMed1992

Synaptic activation of rat adrenal medulla examined with a large photodiode array in combination with a voltage-sensitive dye.

The adrenal medulla is innervated by sympathetic preganglionic nerve fibers in the splanchnic nerve. Synaptic activation of the adrenal medulla causes catecholamine secretion which is known to be modified by various neuropeptides and other factors. To understand the neuronal control mechanism of catecholamine secretion, it is necessary to know the transfer function at the synapse and how it is affected by such factors. By using a large photodiode array in combination with a voltage-sensitive dye, membrane potential changes in a slice of the rat adrenal gland were recorded upon brief local electrical stimulation. Electrical signals were recorded only on the portion of the diode array corresponding to the medulla. In a typical record, a spike and an underlying slow potential were observed following a small deflection due to a presynaptic nerve action potential. Both the spike and slow potential were blocked in Ca(2+)-free solution or by hexamethonium, a nicotinic antagonist, but were not affected by atropine, a muscarinic antagonist. The slow potential was interpreted as a nicotinic synaptic potential in the chromaffin cells and the spike as a population action potential. A double pulse experiment revealed that the chromaffin cell action potential began to fail only when the stimulus interval was less than 50 ms (20 Hz). When the stimulus intensity was reduced, the minimal response was found to behave in an all-or-none fashion. This suggested that one nerve fiber is innervating a cluster of chromaffin cells, which may correspond to a previously histologically identified "complex" of cells [Hillarp (1946) Acta. anat. 4, Suppl. 1]. Each complex was innervated by approximately four nerve fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1992

An improved cryofixation method: cryoquenching of small tissue blocks during microwave irradiation.

The metal contact method of rapid freezing is greatly improved by irradiating the specimen with microwaves at 2.45 GHz for a short period of time (50 ms), while pushing the specimen onto the surface of the copper block cooled by liquid N2. The microwave irradiation, together with two technical improvements (a light-mass plunger and a recently developed beta-gel shock absorber) for preventing bounce, produces a good freezing zone for squid retina, with high reproducibility for each experimental trial, extending from the contact surface to a depth of about 15 microns, which is comparable to the depth obtained by the metal contact method using liquid He in the absence of microwave irradiation. A good freezing zone was also experimentally demonstrated in specimens of rat liver and heart muscle. Microwave irradiation does not have appreciable effects on the ultrastructure of squid retina. The mechanism underlying the improvement in the rapid freezing under the microwave irradiation is discussed.

Animals↗
PubMed1992

A case of congenital dyserythropoietic anemia type II associated with hemochromatosis.

A 54-year-old woman with anemia, diabetes mellitus and liver dysfunction was admitted to our hospital. Numerous binucleated erythroblasts in the bone marrow, a positive serum acidified test, and the presence of anti I and anti i antigens on the surface of her erythrocytes indicated that she had congenital dyserythropoietic anemia (CDA) Type II. Hemochromatosis was confirmed by a liver biopsy. This case is a sibling of a patient with CDA Type II reported by Omine et al in 1981 (Acta Haematol Jpn 44:1). They report that no physical or hematological abnormalities were found when she was examined at the age of 29 years. Twenty-five years later, she developed CDA Type II and hemochromatosis. This case indicates that long-term observation of the family members of a patient with CDA Type II is necessary.

Anemia, Dyserythropoietic, Congenital↗
PubMed1991

Inhibitory effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on the micturition reflex in rat.

The effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an alpha-amino-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor antagonist, on bladder contractions was examined under isometric conditions in urethane anesthetized rats. Intravenous administration of CNQX (33 ng-50 micrograms/kg) inhibited or abolished bladder contraction. Before complete inhibition, the frequency of bladder contractions was reduced without altering the amplitude or duration. Intrathecal administration of CNQX (2 ng/kg-11 micrograms/kg) similarly inhibited bladder contractions. In contrast, CNQX did not affect bladder contractions in chronically spinalized animals (6.7 ng/kg-400 micrograms/kg i.v.), or contractions evoked by stimulation of the decentralized pelvic nerve (1-100 micrograms/kg i.v.).

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1991

Anticalmodulin drugs block the sodium gating current of squid giant axons.

The effects of calmodulin (CaM) antagonists (W-7, W-5, trifluoperazine, chlorpromazine, quinacrine, diazepam, propericyazine and carmidazolium) on the sodium and potassium channels were studied on the intracellularly perfused and voltage-clamped giant axon of the squid. It was found that the drugs are more potent blockers of the sodium current than of the potassium current. The drugs also reduce the sodium gating current. The blockage of the sodium and gating current can be explained by assuming that the drugs interact with the sodium gating subunit in one of its closed states. The site of action is probably the intracellular surface of the axolemma where presumably a Ca(2+)-calmodulin complex can be formed.

Animals↗
PubMed1990

Variation in the pattern of [Ca2+]i change induced by acetylcholine in cultured hippocampal neurons.

Acetylcholine (ACh) caused various patterns of change in the intracellular Ca2+ concentration ([Ca2+]i) in cultured rat hippocampal neurons. We studied the underlying mechanisms of the [Ca2+]i changes with simultaneous recording of [Ca2+]i and membrane potential/current. In most cases, [Ca2+]i rise was accompanied by a membrane depolarization. The [Ca2+]i change was significantly reduced when the membrane was voltage clamped, which implies that most of the [Ca2+]i rise results from the Ca2+ influx through the voltage-gated Ca2+ channel activated by the membrane depolarization. The membrane depolarizations were classified into two types, one associated with membrane conductance decrease and the other associated with membrane conductance increase. The former results from potassium conductance ((gK+) decrease, and the latter may result from the activation of a Na(+)-permeable channel. However, [Ca2+]i elevation was also observed in some neurons showing membrane hyperpolarization in response to ACh. This seems to show that ACh liberates Ca2+ from the intracellular Ca2+ store, resulting in the activation of a calcium-dependent K+ channel (KCa). The variations of ACh response in the hippocampal neurons seem to result from a variety of muscarinic acetylcholine receptors and various species of ion channels governed by those receptors.

Acetylcholine↗
PubMed1990

Simultaneous recordings of cytosolic Ca2+ level and membrane potential and current during the response to thyroliberin in clonal rat anterior pituitary cells.

The response to thyroliberin in prolactin-producing rat GH4C1 clonal cells was studied using fura-2 to monitor the cytosolic Ca2+ level ([Ca2+]i) in single cells, combined with recordings of membrane potential and current. The average value of [Ca2+]i was 109 nM (mean +/- SD, n = 112), and evoked action potentials caused transient elevations of about 100 nM. At higher firing frequencies these transients merged to a sustained elevation. In 100% of the cells thyroliberin caused an instant rise in [Ca2+]i, peaking at 795 +/- 300 nM (n = 112). This first phase of the thyroliberin response was associated with hyperpolarization in current clamp and outward current in voltage clamp, caused by the opening of Ca2(+)-activated K+ channels. In 75% of the cells the initial peak in [Ca2+]i was followed by a prolonged plateau phase at 247 +/- 76 nM (n = 84). In current clamp the second-phase elevation of [Ca2+]i was linked to either a modest depolarization in combination with enhanced firing frequency or a more pronounced depolarization in silent cells. This elevation of [Ca2+]i was reversed by hyperpolarizing current injection. No second-phase elevation of [Ca2+]i was observed during voltage clamp at a holding potential of -50 mV. Short exposure to Ca2(+)-free conditions eliminated the second-phase elevation in [Ca2+]i, whereas the first phase remained intact. Our experiments show a direct relationship between electrical activity and [Ca2+]i in the GH4C1 cells. The second-phase elevation of [Ca2+]i caused by thyroliberin is the result of influx through voltage-sensitive Ca2+ channels, without involving agonist-gated channels.

Animals↗
PubMed1990

Serum type IV collagen concentrations in diabetic patients with microangiopathy as determined by enzyme immunoassay with monoclonal antibodies.

In long-term diabetes mellitus, thickening of basement membrane in capillaries and small vessels is a characteristic lesion and plays an important role in the progression of diabetic microangiopathy. We have developed a sandwich enzyme immunoassay for human serum type IV collagen peptide with monoclonal antibodies. Previous studies suggested that collagen levels reflect the activity of fibrogenesis in basement membrane. Serum type IV collagen levels were measured in 137 non-insulin-dependent diabetic patients (aged 50-75 yr) with or without clinical signs of retinopathy, nephropathy, and/or neuropathy and 110 healthy subjects (aged 50-75 yr) without serological abnormality. Serum concentrations of type IV collagen were significantly higher (P less than 0.01) in diabetic patients (mean +/- SE 124.1 +/- 4.1 ng/ml) than in healthy subjects (73.9 +/- 2.2 ng/ml) and were increased with the prevalence or incidence of diabetic complications. In the patients with diabetic microangiopathy, serum type IV collagen levels became higher as clinical signs worsened. Especially in the patients with diabetic nephropathy, serum type IV collagen levels became higher with elevation of blood urea nitrogen, serum creatinine, and serum beta 2-microglobulin but not urinary excretion of beta 2-microglobulin and N-acetyl-beta-glucosaminidase. These observations indicated that elevation of serum type IV collagen in diabetic nephropathy was related to glomerular filtration dysfunction rather than renal tubular dysfunction. However, the antigen, which can be detected by our assay system, did not exist in urine specimens of healthy subjects, and an intimate relationship was not observed between serum type IV collagen level and serum creatinine level.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Purification and characterization of Ca2+/calmodulin-dependent actin-binding proteins from squid retina.

Ca2+/calmodulin (CaM)-dependent actin-binding proteins (CABPs) of 92, 105, 120 and 135 kDa were purified from squid retina. These proteins were eluted from the CaM affinity column in a Ca2+-dependent manner, and binding of the CABPs to F-actin was regulated by Ca2+/CaM. Electron microscopic observations employing the low-angle rotary shadowing technique showed the CABP molecules to have granular shapes similar to the granular proteins associated with actin filaments in squid rhabdomeral microvilli. We have previously reported that these actin filaments are fragmented upon exposure to light [(1988) J. Cell Biol. 106, 1151-1160]. Since the intracellular Ca2+ concentrations of the invertebrate retina are elevated during the light illumination, these results indicate that the CABPs are directly associated with the actin filament in the microvilli of the squid photoreceptors. We therefore suggest that the CABPs may regulate the light-induced structural changes of the microvillar cytoskeleton.

Actins↗
PubMed1989

Detection-threshold of 50-Hz electric fields by human subjects.

The threshold intensity for detection of an AC electric field was studied in human subjects at several different temperatures and humidities. The dorsum and palm of the hand were exposed to fields, representing hairy and hairless skin, in order to clarify whether hair movement is critical for field detection. Experiments were carried out on human subjects (seven men and four women) during hot humid weather of July-August and dry cool air of October-November. Threshold values obtained in the summer were 30-65 kV/m for the hairy skin on the dorsum of the hand, while for the hairless skin on the palm the threshold was greater than 115 kV/m (highest field available due to limitations of the power supply). During the fall, the threshold was much higher than during the summer. We sought possible reasons for the difference and found that humidity was the main factor. Relative permittivity of woman's hair was then estimated by measuring capacitance of the hairs under dry (35% RH) and wet (85% RH) conditions at 20 degrees C. The values of relative permittivity obtained under these two conditions differed by several times the average. The differences in detection thresholds may be attributable to the different relative permittivities of the hairs under dry and wet conditions.

Adult↗
PubMed1989

Axolinin localization in the nervous tissue of squid revealed by monoclonal antibodies specific for axolinin: cellular and subcellular localization of axolinin in the squid neuron.

Cellular and subcellular distributions of axolinin, the 260-kilodalton (kD) microtubule-associated glycoprotein originally purified from squid axons, in various squid tissues such as optical lobes, bundles of small nerve fibers (fin nerves), giant stellate ganglia, skin, muscle, liver, and gill, were immunologically studied using monoclonal antibodies specifically recognizing the polypeptide chain of axolinin. The following results were obtained: (1) Axolinin is confined to squid neurons and skin; (2) axolinin is localized in the axon whereas another 260-kD microtubule-associated protein, MAP B, is localized in the cell bodies; and (3) axolinin is localized mainly in the peripheral part of the axoplasm of the squid giant axon. The last result has confirmed our previous conclusion obtained using polyclonal antisera against axolinin, which contain antibodies recognizing not only axolinin-specific epitopes but also nonspecific epitopes. The physiological importance of the localization of axolinin in axons and the skin is discussed based on its possible relationship to excitability function.

Animals↗
PubMed1989

[A case of renal cancer complicated with acute hypercalcemia and acute pancreatitis].

A 55-year-old man who had liver metastasis after undergoing surgery for renal cancer was hospitalized immediately on May 4, 1987 with complaints of general malaise, epigastric pain, nausea and vomiting. Because of abnormally high levels of blood calcium 15.6 mg/dl and serum amylase 2,069 IU/l, the case was diagnosed as hypercalcemic crisis and acute pancreatitis. Following recovery from the critical stage with administration of elcatonin and FOY, therapy for cancer initiated. We report the clinical course of this patient and discuss about hypercalcemia and acute pancreatitis as cases of oncologic emergency.

Acute Disease↗