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Biomedical subjects

T Oka

Publications and source records attributed to T Oka.

At least 19 recordsLinked to original sources
PubMed1979

Sodium ions and the development of the inotropic action of ouabain in guinea-pig heart.

Factors that determine the interaction of ouabain with the positive inotropic receptor were examined in isolated perfused guinea-pig hearts. The hearts were exposed to ouabain during a perfusion with a modified Krebs-Henseleit solution. The interaction of ouabain with the inotropic receptors under those conditions was estimated by subsequently perfusing the heart with a regular Krebs-Henseleit solution and monitoring the resting and developed tension. Ouabain failed to cause an increase in the force of contraction when the cardiac tissue was exposed to this agent in the absence of Na+ and Ca2+ either in the presence of a low or high concentration of K+. The absence of Ca2+ or the lack of contraction was not responsible for the failure of ouabain to interact with the inotropic receptor, since the exposure of cardiac tissue to ouabain in a Ca,+-free medium containing Na+ resulted in a development of the positive inotropic effect. Thus, ouabain does not interact with its inotropic receptor in the absence of Na+. The properties of the ouabain-receptor interaction resemble those of ouabain binding to Na+, K+-ATPase. In addition, ouabain increases the mobility of superficially bound Ca2+.

Animals↗
PubMed1979

Induction by lithium ion of multiplication of mouse mammary epithelium in culture.

Lithium ion at concentrations between 2 and 20 mM simulated the stimulatory effects of insulin on the uptake of alpha-aminoisobutyric acid, synthesis of RNA and DNA, and cell multiplication in mouse mammary gland explants cultured in a chemically defined synthetic medium. Other monovalent cations were virtually ineffective. In most instances the stimulatory effect of lithium ion was somewhat smaller than and additive to that of insulin. However, lithium ion was incapable of substituting for the action of insulin in augmenting milk protein synthesis in mammary explants cultured with other lactogenic hormones, prolactin, and glucocorticoid. The observed similarities of the responses of mammary cells to lithium and insulin suggest that possible importance of cation(s) in the regulation of mammary cell proliferation, which may be a common basis for the action of the two agents. On the other hand, the observed inability of lithium to mimic the lactogenic effect of insulin indicates a specific function of the hormone in the functional differentiation of mammary cells.

Animals↗
PubMed1979

Calcium requirements for electrically-induced release of an endogenous opiate receptor ligand from the guinea-pig ileum.

Calcium requirements for electrically-induced release of an endogenous opiate receptor ligand in the myenteric plexus-longitudinal muscle strip of the guinea-pig ileum were studied. The naloxone-reversible depression of the electrically evoked contraction caused by stimulation at 10 Hz in normal Krebs solution was markedly reduced by decreasing the calcium concentration in the solution. The depression was greatly diminished by increasing the magnesium concentration in the solution. These results show that the electrically-induced release of an opiate-like material requires calcium ions.

Animals↗
PubMed1978

Indication and appreciation of operative procedures for mandibular ankylosis.

Mandibular ankylosis may be of various etiology. A number of operative procdures have been presented and criticized, but the most appropriate procedure for ankylosis is not universally accepted. During the past decade, 17 cases of mandibular ankylosis have been treated surgically in the Nagoya University Hospital. The etiology includes both temporomandibular ankylosis and extraarticular origin. Three different surgical procedures were used: (1) High operation, in which skin incision is made in the preauricular region. This method is applied for moderate arthrogenic cases. (2) Low operation, in which skin incision is made in the submandibular region. This is applied for severe arthrogic cases and extraarticular ossification cases. (3) Tubed pedicle skin grafting is applied for buccal contracture cases caused by noma etc. A long-term follow-up to 10 years has disclosed many interesting findings and made it possible to evaluate each operative procedure.

Adult↗
PubMed1978

Peptide bond synthesis catalyzed by alpha-chymotrypsin.

alpha-Chymotrypsin [EC 3.4.21.1] catalyzed the syntheses of peptide bonds with various N-acylated amino acids or peptides having aromatic or hydrophobic amino acid residues at the C-terminal position as carboxyl components, and amino acid derivatives, peptides or their derivatives as amine components. A neutral pH was most efficient and quite high concentrations of alpha-chymotrypsin and starting materials were required for synthesis. Four amine components, hydrophobic or bulky amino acid residues were useful at the N-terminal position. Stereospecificity was also observed at the N-terminal position of amine components. Peptide synthesis was not usually seen when the products were soluble in the reaction mixture. This could be partly overcome by increasing the concentration of either the carboxyl or the amine component to more than ten times that of the other.

Amines↗
PubMed1978

Effect of beta-lactam antibiotics on in vitro peptidoglycan cross-linking by a particulate fraction from Escherichia coli K-12 and Bacillus megaterium KM.

The binding constants of several beta-lactam antibiotics towards penicillin-binding components in Escherichia coli K-12 (Spratt, Eur. J. Biochem. 72:341-352, 1977) and the antibiotic concentrations required to inhibit the peptidoglycan transpeptidase of E. coli 50% were compared. Penicillin-binding component 1B may have been the transpeptidase working in vitro. The structure-activity relationships of beta-lactam antibiotics and the mechanisms of action in E. coli and Bacillus megaterium are discussed.

Bacillus megaterium↗