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Biomedical subjects

T Osa

Publications and source records attributed to T Osa.

At least 19 recordsLinked to original sources
PubMed1998

Layer-by-layer construction of enzyme multilayers on an electrode for the preparation of glucose and lactate sensors: elimination of ascorbate interference by means of an ascorbate oxidase multilayer.

A layer-by-layer structure of enzyme multilayers composed of glucose oxidase (GOx) or lactate oxidase (LOx) and ascorbate oxidase (AOx) was prepared on the surface of a platinum electrode. The amperometric response to glucose or lactate was studied in the presence of ascorbic acid as a possible interference. An alternating and repeated deposition of avidin and the biotin-labeled enzymes resulted in the layer-by-layer structure of GOx/AOx and LOx/AOx multilayers. Optical and gravimetric measurements based on an ultraviolet-visible absorption spectroscopy and a quartz crystal microbalance revealed that the enzyme multilayers thus prepared consist of monomolecular layers of the proteins. The GOx/AOx and LOx/AOx enzyme multilayers were useful to eliminate ascorbic acid interference in the glucose and lactate biosensors, because ascorbic acid can be converted to an electrochemically inert form, dehydroascorbic acid, before being oxidized directly on the Pt electrode. Thus, the GOx/AOx or LOx/AOx multilayer-modified biosensors can be used to determine the normal blood level of glucose (5 mM) and lactate (1 mM) in the presence of a physiological level of ascorbic acid (0.1 mM). The effects of the number of the AOx layers and geometry of the enzyme layers in the multilayer on the performance characteristics of the biosensors are discussed.

Ascorbate Oxidase↗
PubMed1996

Adsorption behavior of serum albumin on electrode surfaces and the effects of electrode potential.

The adsorption behavior of serum albumin onto the surface of platinum, gold, and glassy carbon electrodes was studied in relation to the electrode potential, by using cyclic voltammetry and a quartz-crystal microbalance. The kinetics of adsorption was significantly dependent on the electrode potential. The adsorption was highly accelerated by the application of positive potential to the electrode, suggesting an electrostatic interaction between the negatively charged albumin molecules and the positively polarized electrode as the origin of the accelerated adsorption. The adsorption of albumin on the electrodes was irreversible with respect to dilution of the albumin solution, while the quartz-crystal microbalance data showed that albumin forms a monomolecular layer on the electrode surface. Protein adsorption on electrode surface in serum was also examined.

Adsorption↗
PubMed1996

Modification of a glassy carbon electrode with diols for the suppression of electrode fouling in biological fluids.

The surface of a glassy carbon (GC) electrode was modified covalently with ethyleneglycol, diethyleneglycol, 1,2-propanediol, and 1,3-propanediol by electrochemical oxidation in order to suppress the electrode fouling originating from non-specific adsorption of serum proteins. Human serum albumin (HSA) was adsorbed significantly on the surface of a bare GC electrode, which was monitored by cyclic voltammetry in the presence of Fe(CN)6(4)-/Fe(CN)6(3)-ions. In contrast, the diol-modified GC electrodes were scarcely fouled in HSA solution and even in human serum. The results were explained reasonably based on the hydrophilic nature of the diol-modified GC surface.

Adsorption↗
PubMed1995

Controlled deposition of glucose oxidase on platinum electrode based on an avidin/biotin system for the regulation of output current of glucose sensors.

A facile method for the regulation of enzyme loading on an electrode surface has been studied using avidin and biotinylated glucose oxidase (GOx). It was demonstrated that an alternate and repeated deposition of avidin and biotinylated GOx gives a protein thin film probably composed of avidin monolayers and biotinylated GOx monolayers which are connected with each other through strong affinity between avidin and biotin moieties of the enzyme (binding constant, 10(15) M-1). Amperometric response of the glucose sensors constructed by this method was controlled stepwise and rather precisely by regulating the number of GOx layers deposited (or the loading of GOx). For example, the output current of the sensors to 1 mM glucose was enhanced to ca. 1300 and 2800 nA after deposition of 10 and 20 layers of GOx, respectively, as compared with 110 nA for the monolayer GOx sensor. The enhanced response contributed to the extension of the dynamic range of the sensors, especially at a lower glucose concentration. The response time of the sensors was satisfactorily fast (ca. 20 s), irrespective of the number of GOx layers.

Avidin↗
PubMed1995

Influence of intracellular Mn on the contractile inhibition caused by db cAMP, forskolin, and porcine relaxin in the circular muscle of the estrogen-treated rat uterus.

Whether Mn ion permeates into circular muscle cells of the estrogen-treated rat uterus and how contractile inhibitions caused by db cAMP, forskolin, and relaxin are affected by treatment with Mn were examined. By exposing the muscle strip to 0.35 mM Mn added to Mg-free Krebs solution, the magnitude of phasic contractions evoked by electrical stimulation was reduced to 21.8 +/- 14.7% (n = 22) of control. Mn influx was measured by fura-2 fluorescence quenching at the Ca isosbestic excitation wavelength (360 nm). The contractile inhibitions caused by 30 microM db cAMP and 0.2 microM forskolin were enhanced after pretreatment with 0.35 mM Mn for 10 min, whereas the inhibition caused by 100 mU relaxin underwent enhancement or attenuation. These results are discussed in relation to those reported previously for the longitudinal muscle in which the influences of treatment with Mn were somewhat different.

Animals↗
PubMed1994

Pretreatment with porcine relaxin and Mg ions enhances inhibitory effects of dibutyryl cyclic AMP in longitudinal muscle of estrogen-treated rat myometrium.

Phasic contractions were evoked in Mg-free Krebs solution by electrical stimulation in the longitudinal myometrial strip taken from estrogen-treated rats, and the application of 30 microM dibutyryl cyclic AMP (db cAMP) for 15 min depressed the amplitude of contraction to 81 +/- 18% (+/- SD, n = 23) of the control. The contractile depression caused by db cAMP was not significantly altered by pretreatment with either 1 mM Mg (40 min) or 100 mU porcine relaxin (15 min) alone; however it was markedly enhanced to 22 +/- 30% (n = 7) of the control response by the combined pretreatment with Mg and relaxin. The enhancement lasted for longer than 2 h thereafter in Mg-free Krebs solution. It was discussed that some memory factor was induced by relaxin in the presence of 1 mM Mg to respond strongly to db cAMP.

Animals↗
PubMed1994

Effects of Mg and Mn ions on the inhibitory action of cyclic nucleotides in the longitudinal myometrium of rat.

Contractile response, membrane activity, and fluorescence signal from mag-fura-2 were measured on the longitudinal myometrium taken from estrogen-treated rat, and the influence of Mg and Mn ions on the inhibitory effects caused by db cAMP, 8-bromo cGMP, and db cGMP was investigated. Taking the Kd value of mag-fura-2 with Mg to be 2.0 mM, the intracellular Mg concentration was estimated to be 380 microM in the tissue incubated with Mg-free Krebs solution and 420 microM in the tissue exposed to Ca-free 40 mM K solution containing 15 mM Mg for 5 min, respectively. The phasic contractions generated by electrical stimulation in Mg-free Krebs solution were more strongly depressed by 30 microM db cAMP, 10 microM 8-bromo cGMP, and 1 mM db cGMP after the Mg loading treatment. The muscle was exposed to Ca-free 40 mM K solution containing 0.6 mM Mn for 10 min, and it was assumed that the muscle was loaded with Mn ions. After the Mn loading treatment, the contractile depression caused by 8-bromo cGMP and db cGMP was enhanced, whereas that by db cAMP was attenuated. These results were discussed in relation to the influence of intracellular load with Mg or Mn on the inhibitory actions caused by isoprenaline, forskolin, and relaxin.

Animals↗
PubMed1993

Influence of Mn ion the action of dibutyryl cyclic AMP and forskolin on contraction, membrane response, and cyclic AMP-dependent protein kinase activity in rat myometrium.

Contractile response, membrane activity, and protein kinase A (PKA) activity were measured on the longitudinal muscle taken from the estrogen-treated rat uterus, and the influence of Mn ion on the inhibitory effects caused by db cAMP and forskolin was investigated. Phasic contractions generated in the muscle taken from the middle portion of uterus were depressed to 48 and 83% by 30 microM db cAMP and 0.1 microM forskolin in Mg-free Krebs solution, respectively; phasic contractions were more strongly depressed by the agents in the solution containing 0.2 mM Mn. Action potentials consisted of spike and plateau components, and the duration of the plateau potential was reduced by the application of the agents; membrane activity was more strongly depressed in the presence of 0.2 mM Mn. The contractile depression caused by db cAMP was reduced and by forskolin was enhanced by pretreatment of the tissue with 0.6 mM Mn for 30 min. The PKA activity was increased by 39 and 6% of the control, when 30 microM db cAMP and 0.1 microM forskolin were applied, respectively; the PKA activity in response to db cAMP and forskolin was reduced and enhanced, respectively, when the tissues were pretreated with 0.6 mM Mn. It was proposed that Mn ions permeated into cell interior when the muscle was exposed to 0.6 mM Mn, so that the effects of the agents were differently affected. It was also shown that plateau potential dominated in the muscle taken from the ovarian portion, and the contractile inhibition caused by the agents was far weaker.

Action Potentials↗
PubMed1991

Effects of porcine relaxin on contraction, membrane response and cyclic AMP content in rat myometrium in comparison with the effects of isoprenaline and forskolin.

1. The longitudinal muscle from the uterus of oestrogen-treated rats was quiescent in Mg-free Krebs solution. Electrical stimulation generated phasic contraction, which was depressed to 35% and 18% by 50 mu and 150 mu porcine relaxin, respectively. 2. The phasic contractions were more strongly depressed to 26% by 50 mu relaxin in solution containing 0.6 mM Mg, and the depression lasted for more than 4 h after the removal of relaxin. During the persisting depression, raising the external Ca to 7.5 mM did not restore the contraction, but the contraction was restored by removal of Mg. 3. The depression of the phasic contraction by relaxin, examined in Mg-free solution, was enhanced and reduced by pretreatment of the tissue with 0.6 mM Mg and 0.6 mM Mn, respectively, for about 15 min. In contrast, the depression of contraction by isoprenaline or forskolin was enhanced by pretreatment with either Mg or Mn. 4. The cellular content of cyclic AMP was measured in Krebs solution containing 0.6 mM Mg. The values were 1.24 (pmol mg-1 protein) in control solution, and 2.31 and 1.56 when the tissues were treated with 150 mu relaxin and 10(-9) M isoprenaline, respectively. 5. The cyclic AMP production in response to 10(-7) M forskolin measured in Mg-free solution was enhanced when the tissue was pretreated with either 0.6 mM Mg or Mn for 15 min. The cyclic AMP production in response to 100 mu relaxin was increased when the tissue was pretreated with 0.6 mM Mg, and was unchanged by pretreatment with Mn. The cyclic AMP production in response to 10(-9) M isoprenaline was unchanged by pretreatment with the divalent cations. 6. The membrane potential of the muscle was -60.8 mV in Krebs solution containing 0.3 mM Mg, and electrical stimulation induced an action potential which consisted of spike and plateau components. Application of 150 mu relaxin reduced the duration of the plateau; the contractions were progressively depressed. The resting membrane potential and membrane resistance were unchanged by application of 150 mu relaxin. The membrane was hyperpolarized by 2.8 mV, accompanied by a decrease in membrane resistance, when 10(-9) M isoprenaline was applied. 7. Although there were several differences between the effects of relaxin and isoprenaline, it is probable that some process, which is cyclic AMP-dependent, accelerated by Mg and depressed by Mn, is involved in the depressant action of relaxin on contraction.

Adrenergic beta-Agonists↗
PubMed1991

[Relaxin and myometrial activity].

The research on intracellular signal transduction and the smooth muscle contraction have made much progress since 1970. Effects of relaxin, a peptide hormone mainly produced and released from ovary, are reviewed in the above point of view. Cyclic AMP content in myometrial cells is increased by relaxin. One site of relaxin action can be the suppression of myosin light chain kinase activity. Another effect of relaxin is the suppression of action potential, whereby the Ca-influx is reduced. However, relaxin up to 300 mU does not hyperpolarize the myometrial membrane of estrogen-primed rat, which differs from the adrenergic beta-action. Unrealed signal transduction seems involved in the relaxin action.

Action Potentials↗
PubMed1989

Augmentation by external Mg ions of beta-adrenoceptor-mediated actions in the longitudinal muscle of rat uterus.

1. The longitudinal muscle isolated from the uterus of oestrogen-treated rats was not spontaneously active in Locke solution, and electrical stimulation evoked phasic contraction. Isoprenaline (3 x 10(-11) - 10(-8) M) and dibutyryl cyclic AMP (db cyclic AMP, 0.1-0.8 mM) depressed the phasic contraction; the depression was enhanced in the presence of 0.6 mM Mg. 2. The contracture generated by 40 mM K was partially relaxed by isoprenaline (10(-11) - 10(-8) M) and db cyclic AMP (0.1-0.8 mM). Mg (0.6 mM) enhanced the isoprenaline-induced relaxation, but not that induced by db cyclic AMP. 3. The membrane potential of the muscle was -61 mV, and electrical stimulation induced an action potential which consisted of spike and plateau components. Application of isoprenaline and db cyclic AMP mainly reduced the duration of the plateau potential. The effect was potentiated by 0.6 mM Mg. 4. The membrane was hyperpolarized, accompanied by a decrease in membrane resistance, when 10(-8) M isoprenaline or 0.8 mM db cyclic AMP was applied. The effects of isoprenaline were prominently augmented in the presence of 1.2 mM Mg, while those of db cyclic AMP were slightly potentiated. 5. Forskolin (0.1 microM) or papaverine (10 microM) inhibited the phasic contraction and the K-contracture. The effect on the phasic contraction was potentiated by 0.6 mM Mg, while that on the K-contracture was not affected. 6. Forskolin shortened the action potential at 0.3 microM, and hyperpolarized the membrane with a decrease in membrane resistance at 3.0 microM. The membrane effects were augmented by 0.6 and 1.2 mM Mg, respectively. 7. It was hypothesized that external Mg ions could affect at least two processes involved in actions at beta-adrenoceptors on rat myometrium; receptor-agonist interaction and cyclic AMP-mediated inhibition of membrane excitability.

Animals↗
PubMed1989

Photo-switchable ion and enzyme sensors. Photoinduced potentiometric response of glassy carbon electrode coated with polymer or polymer/enzyme dual membrane.

Photo-switchable ion and enzyme sensors were fabricated by the use of glassy carbon electrode coated with nonactindoped or enzyme modified poly(vinyl chloride) (PVC) membranes. The ion sensor with nonactin-doped PVC membrane, which contained spirobenzopyran as the photosensitive dye, exhibited a potentiometric photoresponse to NH4+ ion in the solution. The dynamic range of the NH4+ ion sensor was 10(-7)--10(-3) M. Urea, adenosine, and asparagine sensors were prepared by coating the surface of the NH4+-ion sensor with urease, adenosine deaminase, and asparaginase membranes, respectively. These enzyme sensors could be used for determining the substrates at the micro mole level. The performance characteristics of these sensors were compared with those previously prepared membrane electrode sensors.

Carbon↗
PubMed1989

Enzyme sensors based on an ion-sensitive field effect transistor coated with Langmuir-Blodgett membranes. Use of polyethyleneimine as a spacer for immobilizing alpha-chymotrypsin.

A highly branched polyethyleneimine (PEI) was used as a spacer for immobilizing alpha-chymotrypsin on the surface of Langmuir-Blodgett (LB) membranes which were deposited on the gate of an ion-sensitive field effect transistor (ISFET). alpha-Chymotrypsin could be covalently immobilized through the glutaraldehyde-activated PEI on the LB membrane-coated ISFET. The alpha-chymotrypsin-modified ISFET showed a potentiometric response to the substrate at concentrations of more than 0.1 mM. Some performance characteristics of the sensor, such as pH response, response time, and long-term stability were examined.

Chymotrypsin↗