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Biomedical subjects

K Sumikawa

Publications and source records attributed to K Sumikawa.

At least 163 records · Page 9Linked to original sources
PubMed1984

Partial purification and functional expression of brain mRNAs coding for neurotransmitter receptors and voltage-operated channels.

Poly(A)+ mRNAs extracted from embryonic chicken brain and from adult rat brain were fractionated on sucrose density gradients. The fractions were subsequently injected into Xenopus oocytes where the mRNA was translated. The products were processed and incorporated into the oocyte membrane where they formed functional neurotransmitter receptors and voltage-operated channels. Different mRNA fractions induced the incorporation of different transmitter receptors and voltage-operated channels into the oocyte membrane. These experiments provide a useful step towards the understanding of the structure and function of neurotransmitter receptors and channels.

Animals↗
PubMed1983

Arrhythmogenic plasma levels of epinephrine during halothane, enflurane, and pentobarbital anesthesia in the dog.

Plasma levels of epinephrine which correspond to the arrhythmogenic doses were determined during halothane, enflurane, and pentobarbital anesthesia in the dog. The arrhythmogenic dose was established by a series of 3-min infusion of epinephrine at 10-min intervals. The mean values of the arrhythmogenic doses and the corresponding plasma levels of epinephrine were: 2.18 micrograms X kg-1 X min-1 and 38.7 ng/ml during halothane; 11.43 micrograms X kg-1 X min-1 and 206.3 ng/ml during enflurane; and 15.27 micrograms X kg-1 X min-1 and 296.5 ng/ml during pentobarbital anesthesia. The arrhythmogenic plasma levels of norepinephrine during halothane anesthesia was nearly the same as that of epinephrine.

Anesthesia, General↗
PubMed1983

Selective actions of intravenous anesthetics on nicotinic- and muscarinic-receptor-mediated responses of the dog adrenal medulla.

The selective actions of intravenous anesthetics on the cholinergic nicotinic and muscarinic responses of adrenal medullary cells were studied using isolated dog adrenals perfused with modified Locke's solution. Log-probit dose-response curves of the inhibitory effects of the anesthetics on the catecholamine releases induced by acetylcholine, nicotine, and muscarine were determined. Percentage inhibition by the anesthetics at clinically relevant concentrations were 98% of nicotine- and 31% of muscarine-induced releases by alphaxalone 2.6 microM, 76% of nicotine and 13% of muscarine by thiopental 23.9 microM, 86% of nicotine and no inhibition of muscarine by ketamine 17.0 microM, and no inhibition of either response by diazepam 5.0 microM. The ratio of IC50 (concentration for 50% inhibition), which was calculated by dividing IC50 for muscarine by IC50 for nicotine, showed a variety of values ranging from 3.9 for diazepam to 38.0 for ketamine. The results suggest that each anesthetic has characteristic selective inhibitory effects on nicotinic and muscarinic cholinergic responses. The differing effects on the muscarinic responses might be one of the factors contributing to the characteristic properties of each anesthetic, whereas the inhibition of nicotinic responses might reflect a common property for many anesthetics.

Adrenal Medulla↗
PubMed1982

Synthesis of chick brain GABA receptors by frog oocytes.

Poly(A)-mRNA, extracted from the optic lobe of chick embryos, directs the synthesis of gamma-aminobutyric acid (GABA) receptors in Xenopus laevis oocytes. The receptors are inserted into the oocyte membrane, where they form receptor--channel complexes. When activated by GABA, and related agonists, the chick brain receptors open membrane channels that are permeable to chloride ions. Thus, Xenopus oocytes provide a novel and useful approach to the study of brain receptors.

Animals↗
PubMed1982

The molecular cloning and characterisation of cDNA coding for the alpha subunit of the acetylcholine receptor.

A rare cDNA coding for most of the alpha subunit of the Torpedo nicotinic acetylcholine receptor has been cloned into bacteria. The use of a mismatched oligonucleotide primer of reverse transcriptase facilitated the design of an efficient, specific probe for recombinant bacteria. DNA sequence analysis has enabled the elucidation of a large part of the polypeptide primary sequence which is discussed in relation to its acetylcholine binding activity and the location of receptor within the plasma membrane. When used as a radioactive probe, the cloned cDNA binds specifically to a single Torpedo mRNA species of about 2350 nucleotides in length but fails to show significant cross-hybridisation with alpha subunit mRNA extracted from cat muscle.

Amino Acid Sequence↗
PubMed1982

Similarity of acetylcholine receptors of denervated, innervated and embryonic chicken muscles. 1. Molecular species and their purification.

Acetylcholine receptors were purified to homogeneity from chicken embryonic, adult innervated and denervated muscles, by bio-specific chromatographies using immobilised alpha-neurotoxin and lentil lectin. A minimum specific activity for the pure receptor was estimated to be 6000 nmol alpha-toxin binding sites/g protein. For analysis, the receptors were radio-iodinated or tritiated to high specific radioactivity with succinimidyl-[2,3-3H]propionate. All of the iodinated protein present in the purified receptor preparation reacted with antibody against the pure acetylcholine receptor from Torpedo marmorata electric organ. In the case of all three muscle types used the same oligomeric forms were obtained. The principal form has a sedimentation coefficient of about 9 S, while a minor species (approximately 5S) was also appreciable in crude preparations of embryonic and denervated muscles. Immunization of rabbits with the homogenous receptor from chicken denervated muscle produced muscle weakness characteristic of experimental autoimmune myasthenia gravis. These antisera were equally reactive towards the receptor --125I-alpha-bungarotoxin complexes from chick innervated and denervated muscles. Likewise, the electrophoretic mobilities of the receptors (9-S form) from all three muscle types were identical, as were the isoelectric points of their complexes with 125I-alpha-bungarotoxin. Collectively, these findings and associated ones on subunit structure denote that the 9-S receptor molecules from junctional and extra-junctional area and embryonic stage of chicken muscle are indistinguishable by all criteria yet applied to them.

Animals↗
PubMed1982

Similarity of acetylcholine receptors of denervated, innervated and embryonic chicken muscles. 2. Subunit compositions.

The native (9-S) form of the acetylcholine receptor, purified from chick embryonic or adult innervated or denervated chicken muscles, was shown in each case to contain three subunits of Mr about 40000 (predominant), 50000 and 54000. The 40000-Mr subunit (termed alpha) appears to exist in two forms; the minor variant form of it, with Mr about 41000, may have a different carbohydrate content. Bromo[3H]acetylcholine, an affinity alkylating reagent for this receptor, labels the 40000-Mr subunit and the accompanying 41000-Mr variant. The apparent ratio of the subunits varies with the several methods of detection used (protein staining, radio-iodination or tritiation) but the alpha subunit always predominates. The alpha subunit was separated in urea gel isoelectric focusing; its isoelectric point was identical there for the three receptors from innervated, denervated and embryonic muscles. Their respective peptide maps for alpha subunit were identical, and likewise for the 54000-Mr subunit. All of the evidence obtained shows that the subunit structures of the junctional, extra-junctional and embryonic chick muscle receptors are identical. Although the alpha subunit in the receptor from Torpedo electric organ, cat muscle and chicken muscles is distinguishable in all three cases in dodecylsulphate gel electrophoresis, it is affinity-labelled in each case. The peptide map of this subunit after limited proteolysis is also very similar in all three cases. It is concluded that the alpha subunits from these three diverse sources are closely related structurally.

Animals↗
PubMed1982

Translation of exogenous messenger RNA coding for nicotinic acetylcholine receptors produces functional receptors in Xenopus oocytes.

Messenger RNA extracted from the electric organ of Torpedo was injected into Xenopus oocytes. This led to the synthesis and incorporation of functional acetylcholine receptors into the membrane of the oocyte. When activated by acetylcholine these Torpedo acetylcholine receptors in the oocyte membrane opened channels whose ionic permeability resembled that of nicotinic receptors in other cells.

Animals↗
PubMed1982

Mechanism of the differential effects of halothane on nicotinic- and muscarinic-receptor-mediated responses of the dog adrenal medulla.

The mechanism of the differential effects of halothane on the cholinergic nicotinic and muscarinic responses of adrenal medullary cells was studied using isolated dog adrenals perfused with modified Locke's solution. The concentrations of halothane exhibiting 50% inhibition of catecholamine release induced by nearly equipotent agonists were 0.8% for nicotine, 1.9% for acetylcholine, and 2.8% for muscarine, respectively. Per cent inhibition by halothane (1.5%) of nicotine-induced catecholamine release was 98.5%, and those of veratridine-, acetylcholine-, CaCl2-, Na+-deprivation- and muscarine-induced catecholamine release were 89.7, 32.5, 21.4, 10.1, and 9.5%, respectively. Halothane showed an inhibitory effect on the agonist-induced catecholamine release in Na+-free solution to the same extent as in Na+-containing solution. Tetrodotoxin abolished veratridine-induced catecholamine release completely and decreased nicotine-induced release slightly, whereas it had no effect on either muscarine- or acetylcholine-induced catecholamine release. Verapamil inhibited acetylcholine-induced catecholamine release by 65%, and nicotine- and muscarine-induced release by 79% and 26%, respectively. The results suggest that halothane at clinical concentrations selectively inhibits the nicotinic-receptor-mediated responses of the dog adrenal medulla. The mechanism involved might be the susceptibility to halothane of the Ca++ channels that are linked to the respective nicotinic and muscarinic receptors. An inhibition of exocytosis might be also indicated as part of the effect of halothane.

Acetylcholine↗