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T Osa

Publications and source records attributed to T Osa.

At least 37 records · Page 2Linked to original sources
PubMed1989

Comparison of Mg, Mn, and Co ions affecting the beta-adrenoceptor-mediated membrane response in the guinea-pig taenia caeci.

Electrical activity was recorded intracellularly from the muscle cell of guinea-pig taenia caeci in Locke solution. Membrane potential was -46.4 mV, and spike potentials were discharged spontaneously. Isoprenaline (3 microM) hyperpolarized the membrane and suppressed the spike discharge. The hyperpolarization by isoprenaline was increased at low K (2 mM), while decreased at high K (11.8, 29.5, 59 mM). The hyperpolarization by isoprenaline was potentiated in the presence of external Mg ions, depending on the concentration of Mg (0-9.6 mM). Forskolin (3 microM) and papaverine (30 microM) hyperpolarized the membrane; the effects were augmented by 1.2 mM Mg. The hyperpolarization in response to 3 microM isoprenaline or 100 microM papaverine was inhibited by Mn, Co, and low Ca (1 mM) whereas it was not affected by high Ca (7.5 mM). Verapamil (0.5, 2 microM) had no influence of the hyperpolarization caused by isoprenaline. It was discussed that extracellular and/or intracellular Mg and Ca ions played important roles in the beta-adrenoceptor-mediated action on the smooth muscle membrane of taenia caeci.

Animals↗
PubMed1988

Postpartum changes in the mechanical responses of the circular muscle of rat uterus.

The circular muscle strips were isolated from rat uterus 10-60 h after parturition, and the electrical and mechanical responses were investigated. The muscle strips exhibited a variety of contractile activity ranging from frequent spontaneous contractions generated on an elevated muscle tone to a sustained contracture, when incubated with Mg-free Krebs solution. The muscle tone was lowered, and phasic contractions were abolished when the external Ca was removed. Muscle tone was also lowered by addition of 1.2 mM Mg, 1 mM spermidine, or 1 mM tetracaine. The membrane potential was about -25 mV in a muscle which exhibited a contracture, and the membrane was hyperpolarized by 20-25 mV by the (1.5-4.5 x 10(-5) M) caused a gradual decrease in muscle tone, and the that Ca-influx was increased, for which prostaglandin(s) was membrane was hyperpolarized. In view of the above results, it is hypothesized that Ca-influx was increased, for which prostaglandin(s) was probably responsible, in the circular muscle of postpartum rat uterus, thereby elevating the muscle tone in Mg-free solution.

Animals↗
PubMed1988

Effects of cytochalasins on the mechanical and membrane responses in the isolated longitudinal myometrium of pregnant rat with reference to the EGTA-resistant contraction.

Effects of cytochalasins B and D (CB, CD) were examined for the contractions of the longitudinal myometrium of pregnant rat exposed to Krebs solution, 40 mM K Krebs, and Ca-free (40 mM K) solution containing 5 mM Mg. The Ca-free contraction was evoked by applying 3 mM ATP. Application of CB caused a prompt inhibition of the contractions: 3 microM CB depressed the twitch contraction generated in Krebs solution by 12%, the K-contracture by 6%, and the ATP-induced contraction in the Ca-free solution by 59%. CD (3 microM) depressed the K-contracture by 31%, and the ATP-induced contraction in the Ca-free solution by 81%. CB and CD in 3 microM hyperpolarized the membrane and depressed the generation of action potential. From the above results, it was discussed that depressant effects of cytochalasins on twitch contractions in Krebs solution are at least in part due to the depression of membrane excitability, whereas contractions evoked in high K solutions are depressed by cytochalasins due to their effects on cytoskeleton.

Adenosine↗
PubMed1987

The mechanical response of rat myometrium to adenosine triphosphate in Ca-free solution.

The contractile response of the myometrial longitudinal muscle of pregnant and estrogen-treated rats to adenosine triphosphate (ATP) was investigated. ATP (10(-5)-4 X 10(-3) M) added to Krebs solution caused a generation of spontaneous activity consisting of phasic contractions and an elevation of muscle tone in a dose-dependent manner. Effects of the "test solution" consisting of isotonic K, 4(mM) ATP, 4 Mg, 1-20 EGTA, 20 tris(hydroxymethyl)aminomethan (Tris) maleate (pH 6.8) on the contractile response was then investigated. An initial phasic and a following tonic contraction was evoked by the application of the test solution, when applied after the equilibration of the muscle with Krebs solution. ATP was proved to be an agonist to evoke the Ca-free contraction. The phasic contraction was depressed when the muscle was incubated with Ca-free Krebs solution. The amplitude of the tonic contraction became progressively larger when application of the test solution was repeated. The amplitude was 15-70% as large as the tonic component of the K-contracture induced by 40 mM K. Theophylline (10 mM), 0.1 mM papaverine and 1 microM isoprenaline nearly abolished, and 1 mM cAMP partly depressed the tonic contraction of K-contracture, whereas the tonic contraction induced by the test solution was unaffected. A calmodulin antagonist, W-7 (100 microM) strongly suppressed both the K-contracture and the contraction induced by the test solution, whereas trifluoperazine (10-200 microM) preferentially depressed the K-contracture. The tonic contraction induced by the test solution was strongly depressed when Mg was removed and 20 mM EDTA was applied. From these results, it is discussed that some Ca-independent process is involved in the generation of tonic component of Ca-free contraction developed by the application of the test solution.

Adenosine Triphosphate↗
PubMed1987

The mechanical response of the isolated longitudinal muscle of pregnant rat myometrium to adenosine triphosphate in the Ca-free solution containing various polyvalent cations.

A small tonic contraction could be evoked by 3 mM adenosine triphosphate (ATP) in the longitudinal muscle of pregnant rat myometrium which was incubated with the Ca-, Mg-free solution containing 2 mM EGTA (40 mM K). The amplitude of the tonic contraction was decreased by exposure to the solution within a few hours, but was again increased when 1-10 mM Mg was added to the Ca-free solution. The ATP-induced contraction was increased for more than 7 h during exposure to the Ca-free solution containing Mg ions. The ATP-induced contraction in the Ca-free (Mg-free) solution was also produced when the solution contained 1 mM Mn or 1.5 mM La. On the other hand, the tonic contraction evoked by 1 mM Ca or Ba in the presence of 40 mM K was depressed by ATP. The above results led us to propose that the ATP-induced contraction evoked in the Ca-free solution containing Mg was mediated by a process independent of Ca, and possibly mediated by a translocation of Mg in the cell. La and Mn could take the place of Mg in producing a tonic contraction caused by ATP application.

Action Potentials↗
PubMed1987

Electrophysiological effects of tetracaine on the longitudinal muscle of rat uterus in various ionic environments.

Electrical activity was recorded intracellularly from the uterine longitudinal muscle of estrogen-treated rat. Membrane potential was -59 mV. Action potential consisted of initial spike and the following plateau potential on which repetitive spike discharge rode. Tetracaine (0.1, 0.2 mM) reduced the maximum rates of rise and fall of initial spike and increased the duration of plateau potential. Sustained depolarization at -33 mV was produced by the application of 0.8 mM tetracaine. The membrane depolarization was accompanied with the increase in membrane resistance. Reduction of initial spike by tetracaine in the maximum rates of rise and fall was prevented by increasing the external Ca concentration and accelerated by decreasing it. In low K (1.2 mM) or isoprenaline (10(-8) M)-containing solution, tetracaine-induced prolongation of plateau potential was inhibited. Plateau potential was reduced in amplitude and was prolonged only slightly by tetracaine in low Na solution (sucrose substitution). Both the initial spike and plateau potentials were blocked completely by 0.2 mM tetracaine in the presence of Mn (0.5 mM) or verapamil (0.5 microM). It is speculated that tetracaine suppresses the K conductances responsible for resting membrane potential and the repolarizations of spike and plateau potentials. Ca influx during the generation of action potential is also supposed to be inhibited by tetracaine.

Action Potentials↗
PubMed1986

Comparative effects of Mg, Ca, Sr, and verapamil on the uterine longitudinal muscle of spayed and estrogen-treated rats.

A comparison was made of effects of Mg, Ca, Sr, or verapamil on the mechanical and electrical activities in the uterine longitudinal muscles of spayed and estrogen-treated rats. The muscle strips taken from spayed rat exhibited spontaneous rhythmic activity in the Locke solution which did not contain Mg, whereas spontaneous activity was less frequent in the preparation taken from estrogen-treated rat. The resting potentials were -54 and -61 mV in the spayed and the estrogen-treated preparations, respectively. An initial spike potential followed by plateau potential with abortive spikes on the top was generated in both spayed and estrogen-treated preparations. In the spayed preparation, the frequency of rhythmic contractions was reduced, and the base-line tension was lowered when 0.6 mM Mg was added to the solution. The base-line tension was elevated progressively when the external Ca concentration was raised, and reached a maximal value up to 10 mM. The amplitude of phasic contraction was progressively increased by increasing Ca concentrations in the range from 1.25 to 5 mM, and was reduced by Ca higher than 10 mM. In the estrogen-treated preparation, the amplitude of phasic contraction was increased by increasing Ca concentrations in the range from 1.25 up to 17.5 mM. When the amplitude of phasic contraction was increased, the duration of plateau potential became protracted. Substitution of the external Ca with Sr caused an increase in the spike activity generated on the top of plateau potential. However, the amplitude of phasic contraction was diminished in both the spayed and the estrogen-treated preparations. Verapamil (2 microM) caused a stronger depression of electrical and mechanical activity in the spayed preparation. Results were discussed in relation to the genomic effects of estradiol on the membrane properties so as to change the interaction with divalent cations.

Action Potentials↗
PubMed1986

Blockade by cycloheximide of the prepartum changes in membrane activity and adrenergic response of the circular muscle of rat uterus.

A study was made of the effects of cycloheximide, an inhibitor of protein synthesis, on the transformations of electrical activity and adrenergic response of the circular muscle of rat uterus during pregnancy and postpartum. Electrical activity proceeded from plateau type on Day 18 of gestation to spike type on Day 22. Excitatory reaction of the contraction to noradrenaline (10(-7), 3 X 10(-7) M) on Day 18 altered to an inhibitory one on Day 22. When pregnant rats were injected intraperitoneally with 50 micrograms cycloheximide daily from Day 18, the changes mentioned above were suppressed and parturition delayed. In the preparations obtained on Day 21, the excitatory effect of 10(-7) M noradrenaline on the contraction changed to an inhibitory one by in vitro incubation for 7 h with Krebs solution. This transformation was prevented by the incubation with 2 micrograms/ml cycloheximide for 7 h. Membrane activity and adrenergic response turned to plateau-dominant action potential with long duration and potentiation of the contraction by noradrenaline (10(-7), 3 X 10(-7) M) 48 h after parturition, respectively. Cycloheximide (50 micrograms/day, i.p., immediately after delivery and on the next day) failed to inhibit these postpartum changes. The results suggest that the process of protein synthesis is involved in the alterations in electrical activity and adrenergic response of the circular muscle of rat uterus during late pregnancy stage.

Action Potentials↗
PubMed1985

Changes in action potential and beta-adrenergic effects of the circular muscle of postpartum rat uterus.

Spike potential dominated in the circular muscle of postpartum rat uterus during the period between 0 and 15 hr after the delivery of the first newborn. During the postpartum period ranging between 20 and 48 hr, the plateau potential was dominant. Application of 10(-9) M isoprenaline strongly depressed the contraction during early postpartum period (0-15 hr), and the depressant effect was much smaller thereafter. In vivo treatment of postparturient rats with estradiol-17 beta (50 micrograms) or progesterone (50 micrograms) for 2 days did not alter the postpartum change in action potential or the effect of isoprenaline. The postpartum changes in muscle properties mentioned above were prevented in the distended portion of uterus, when several fetuses and placentas were artificially kept inside the uterus for 2 days, while other fetuses were delivered out. The hormonal influences on the circular muscle of postpartum rat uterus were discussed in view of the above experimental findings.

Action Potentials↗
PubMed1985

Effects of polyamines on the mechanical and electrical activities of the isolated circular muscle of rat uterus.

Effects of polyamines (0.05-1.2 mM) on the mechanical and electrical activities in the circular muscles of pre-(day 20 of pregnancy) and post-partum (10-15 h after delivery) rat myometria were studied. In the prepartum preparations, spermine and spermidine, added to the Mg-free Krebs solution, depressed contractions in a dose-dependent manner, whereas cadaverine and putrescine potentiated them. The latter agents depressed contractions when preparations were treated with indomethacin. Plateau potentials were spontaneously generated in the Mg-free solution in the prepartum circular muscle. The duration of the plateau became shorter, and spike potentials supermounted on the plateau potential were depressed when spermine or spermidine was applied. In the postpartum preparations, spike activity was depressed by spermine and spermidine. In both pre- and post-partum preparations, the membrane activity was little affected by cadaverine and putrescine. In view of the above findings, it was hypothesized that polyamines in general took the place of divalent cations in causing membrane stabilization. Cadaverine and putrescine probably caused a potentiation of contraction by stimulating the synthesis of endogenous prostaglandins.

Animals↗
PubMed1984

Kinetic model for isometric contraction in smooth muscle on the basis of myosin phosphorylation hypothesis.

A kinetic model was proposed to simulate an isometric contraction curve in smooth muscle on the basis of the myosin phosphorylation hypothesis. The Ca2+-calmodulin-dependent activation of myosin light-chain kinase and the phosphorylation-dephosphorylation reaction of myosin were mathematically treated. Solving the kinetic equations at a steady state, we could calculate the relationship between the Ca2+ concentration and the myosin phosphorylation. Assuming that two-head-phosphorylated myosin has an actin-activated Mg2+-ATPase activity and that this state corresponds to an active state, we computed the time courses of the myosin phosphorylation and the active state for various Ca2+ transients. The time course of the active state was converted into that of isometric tension by use of Sandow's model composed of a contractile element and a series elastic component. The model could simulate not only the isometric contraction curves for any given Ca2+ transient but also the following experimental results: the calmodulin-dependent shift of the Ca2+ sensitivity of isometric tension observed in skinned muscle fibers, the disagreement between the Ca2+ sensitivity of myosin phosphorylation and that of isometric tension at a steady state, and the disagreement between the time course of myosin phosphorylation and that of isometric tension development.

Animals↗