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T Osa

Publications and source records attributed to T Osa.

At least 55 records · Page 3Linked to original sources
PubMed1984

Changes in the adrenergic effects and membrane activity of the circular muscle of rat uterus during late pregnancy and postpartum.

Circular muscle strips of rat uterus were obtained in the morning on Days 21 and 22 of pregnancy, and on the first postpartum day. Changes in the effects of noradrenaline and isoprenaline due to pregnant stage and incubation period in vitro were investigated, taking the contractile response and membrane activity as indicators. Plateau potential was dominant in Day 21 and postpartum preparations, and spike potential on Day 22. Noradrenaline (3 X 10(-7), 10(-6) M) caused excitation in Day 21 and postpartum preparations, whereas it caused inhibition in Day 22 preparations during early exposure to Krebs solution. When contractile potentiation was caused, plateau potential was prolonged, and when contractile depression was caused the plateau potential was suppressed. By incubation in vitro with Krebs solution, a transformation of the effect of noradrenaline from excitation to inhibition was caused in Day 21 preparations, and from strong to weak inhibition in Day 22 preparations. Isoprenaline of 3 X 10(-10) M concentration markedly depressed the contractile response in Day 22 preparations, whereas 10(-8) M isoprenaline was not enough to suppress the spontaneous contractions in postpartum preparations.

Animals↗
PubMed1984

Effects in vitro of progesterone and estradiol-17 beta on the contractile and electrical responses in rat myometrium.

Uterine longitudinal and circular muscles from pre- and post-term rats were studied in vitro for their contractile and electrical activities under the influence of 20-100 microM progesterone, 20 microM estradiol-17 beta, or 20 microM stilbestrol. Uterine longitudinal or circular muscle strips were irrigated by Krebs solution at 37 degrees C containing one of the hormones mentioned above, dissolved by the use of ultrasonic wave. Muscle contractions were recorded by a force displacement transducer, and electrical activities of the muscle membrane were studied using an intracellular microelectrode. At diestrus and Day 14 of pregnancy, progesterone depressed the contractions of longitudinal muscle. At pre-term, progesterone potentiated the contractions and prolongated the membrane burst discharge of longitudinal muscles, while estradiol inhibited their contractions and suppressed spike activities. At the same stage of pregnancy, both progesterone and estradiol inhibited contractions of circular muscles. At post-partum, progesterone potentiated and then depressed longitudinal muscles, while estradiol inhibited their contractions. At this stage, both progesterone and estradiol inhibited contractions of circular muscles, although vigorous spike discharges were observed. Stilbestrol depressed contractions of both longitudinal muscles from diestrus rats and longitudinal ileal muscles from a guinea pig. In view of these findings, it was deduced that these ovarian hormones exert dual action on the uterine muscle in vitro, one through changes in the membrane activity and the other through dissociation of excitation-contraction coupling.

Action Potentials↗
PubMed1984

Effects of a brief treatment with saponin on the contractile and electrical activities of isolated uterine muscle of pregnant rat.

The isolated longitudinal or circular muscle strip of rat uterus on day 20 of pregnancy becomes quiescent when incubated with Krebs solution for about 2 hr. Electric stimulation gave rise to a twitch-like contraction with a small amplitude instead of the spontaneous phasic contraction observed during the early period of incubation. When saponin (30-500 micrograms/ml) was applied, the basal tension was elevated and spontaneous contractions having large amplitude were elicited. The amplitude was larger than the phasic contraction of the K-contracture observed prior to the saponin treatment. The membrane was depolarized by about 25 mV, and periodic burst discharge was generated at the onset of saponin treatment. Raising the external Mg concentration from 0 to 2.4 mM in steps caused a depression of contractions in a dose-dependent manner before treatment with saponin, whereas the depression by Mg was much reduced after saponin treatment. The saponin-treated muscle recovered to exhibit control activity when tissues were superfused with Krebs solution for hours, i.e. the membrane was repolarized, the duration of action potential was detracted, and the depressant effect of Mg was again potentiated. For comparison, the effects of saponin and Mg on the contractions of ileal longitudinal muscle of pregnant rat were studied. In view of the above observations, the following were discussed. 1. Saponin impaired the depressant effect of Mg on the generation of contractions. 2. The membrane once impaired by saponin recovered in vitro probably under the influence of the genomic effect of ovarian hormones, a phenomenon which appeared characteristic for pregnant uterus.

Animals↗
PubMed1983

Effects of magnesium on the membrane activity and contraction of the circular muscle of rat myometrium during late pregnancy.

Comparative effects of Mg were studied on circular muscle strips of pregnant rat myometrium near term and during delivery. Frequency and amplitude of spontaneous contraction were markedly depressed by adding 0.6 mM Mg to Mg-free Krebs solution in the muscle strips taken in the morning of Days 19 and 22 of pregnancy. Frequency decreased, whereas the amplitude was not depressed by 0.6 mM Mg in muscle strips taken during delivery. Plateau potential dominated in the circular muscle taken in the morning on Days 19 and 22, and it was depressed by Mg, leaving the evoked spike potential nearly unaffected. Burst of spike potentials dominated in the circular muscle during delivery, and 0.6 mM Mg did not affect the burst discharge. In contrast to the variable effects of 0.6 mM Mg on the polarized muscle strips of different pregnant stages, application of Mg (0.6-3.6 mM) caused commonly a potentiation of tonic contraction of K-contracture generated in muscle strips of any pregnant stage. Prolonged perfusion with Mg-free Krebs solution (several hours) of the muscle strip taken in the morning on Day 22 caused a transformation of membrane activity from a plateau dominant type to a spike dominant one. With the same procedure, the depressant effect of Mg on phasic contractions was progressively decreased.

Action Potentials↗
PubMed1983

Effects of magnesium, oxytocin, and prostaglandin F2 alpha on the generation and propagation of excitation in the longitudinal muscle of rat myometrium during late pregnancy.

In order to find out the changes in myometrial properties towards parturition, effects of Mg, oxytocin, and prostaglandin F2 alpha (PGF2 alpha) were investigated on longitudinal muscle strips taken from rat uteri on Days 20 and 22 of pregnancy. With intracellular recording by microelectrode, membrane potential was 50.5 +/- 1.4 mV on Day 20, and 49.9 +/- 1.0 mV on Day 22 in the Mg-free Krebs solution. The slow potential was larger, and the spike potentials during a burst discharge exhibited variable amplitude on Day 20, whereas these were regular on Day 22. With extracellular recording by the rubber gap method, spike potentials discharged in a synchronized manner on Day 22, suggesting a better coordination between cell groups. When 1.2 mM Mg was applied, the spontaneous activity was depressed more strongly on Day 22. The excitatory effect of PGF2 alpha faded sooner, whereas that of oxytocin persisted. When the fading of PGF2 alpha had occurred, the excitatory effect of oxytocin was weaker than when it was given alone. Because propagation of spontaneous activity, occurring either in the Mg-free solution or in the presence of oxytocin and PGF2 alpha in normal Krebs solution, did not show a definite direction from ovarian to vaginal side of the longitudinal muscle, it was concluded that generation of spontaneous activity was not localized in a given site of the muscle, but originated anywhere in Days 20 and 22 preparations.

Action Potentials↗
PubMed1982

Calcium diffusion in uterine smooth muscle sheets.

The potassium contracture in the longitudinal muscle of estrogen-treated rat uterus was kinetically investigated. The rates of tension development after Ca addition and relaxation after Ca removal were measured under the high-potassium depolarization. Both rates decreased with an increase in preparation thickness. The relaxation rate had only a slight dependence on temperature. On the contrary, both relaxation and contraction rates in a contraction induced by an electrical stimulation strongly depended on temperature, but not on preparation size. These results suggest that the Ca diffusion process in the extracellular space is the rate-limiting step in relaxation of Ca-dependent contracture under potassium depolarization. The diffusion model, in which the effect of the unstirred layer was considered, could quantitatively explain the experimental results. The apparent diffusion coefficient in the muscle sheet was estimated to be approximately 3 x 10(-7) cm2/s. The difference from that in aqueous solution is discussed.

Animals↗
PubMed1981

Modification by magnesium and manganese ions of the effects of oxytocin on the electrical and mechanical activity of the longitudinal muscle of estrogen-treated rat uterus.

Ovariectomized rats were given one-shot injections of 10 microgram estradiol-17 beta benzoate, and the longitudinal muscle of the uterus was used for experiment 4 days later. The membrane potential was 58.8 +/- 2.4 mV, and the membrane activity consisted of repetitive spike potentials carried on a plateau potential. Oxytocin (1 mU/ml) caused a depolarization of 7.6 +/- 3.7 mV in a Mg-free Locke solution, a prolongation of burst discharge and increase in the frequency of spontaneous activity. The effects were potentiated by 1-3 mM Mg. Burst discharge was abolished by the application of 0.5 mM Mn, and resumed when 0.1 mU/ml oxytocin was applied. Depolarization up to about - 30 mV and a contracture were caused by 1 mU oxytocin when applied with 1-2 mM Mn. The excitatory effect of oxytocin was depressed by 5 mM Mn. Marked depolarization and contracture were produced by 1 mU oxytocin when the application of Mn was discontinued (rebound phenomenon). The above observations indicate the superficial site of Mg and Mn at low concentration in cooperative action with oxytocin, and an additional site of Mn for the rebound potentiation of contraction and depolarization. It is proposed that oxytocin accelerated Mn influx, and that intracellular Mn participates in electrical and contractile responses due to the application of oxytocin. In this respect, acetylcholine caused a similar effect.

Acetylcholine↗
PubMed1980

Effects of estradiol-17 beta on the membrane response and K-contracture in the uterine longitudinal muscle of ovariectomized rats studied in combination with the Mn action.

The membrane potential was about --50mV, and the spontaneous membrane activity was composed of an irregular discharge of action potentials in the longitudinal muscle of the ovariectomized rat uterus. The membrane potential was increased slightly, and repetitive spike potentials were generated on a plateau potential in uteri of ovariectomized rats injected daily with 5 microgram estradiol benzoate, until the steady effect was built up in 3--4 days. The phasic contraction resulted in a relaxation upon exposure to the isotonic K solution containing 2.2 mM Ca, then a tonic contraction developed in ovariectomized uterus. The phasic contraction decayed slightly and it proceeded into a tonic contraction in estrogen-treated uteri. The amplitude of the tonic contraction became larger when the external Ca concentration was raised, and the dose-response relationship shifted to the lower range of the external Ca concentration in the estrogen-treated uterus. In the Ca-depleted solution, the tonic contraction subsided and a contraction was generated when Mn was applied. The change in the configuration of the K-contractures depending on the estrogenic treatment was ascribed to an increase in the Ca influx upon K-depolarization forming greater tonic contraction.

Animals↗
PubMed1979

Influence of magnesium on the beta-inhibition of catecholamines in the uterine circular muscle of estrogen-treated rats.

The effects of Mg and isoprenaline on the uterine circular muscle of ovariectomized rats which were injected with estradiol for 2--6 days were investigated. The muscle strip exhibited an action potential that was composed of a spike and a plateau, and also exhibited a twitch-like contraction due to electrical stimulation. The duration of the action potential became longer when the treatment with estrogen was applied until the maximal effect was built up in 4--5 days. Both the duration of the action potential and the amplitude of contraction were reduced when isoprenaline was applied. When Mg (0.5 mM) was added to the bathing solution these beta-effects were progressively potentiated and the maximal effect was obtained in about 1 hr. An increase in membrane conductance was induced by the application of isoprenaline in a control Locke solution and it was further accelerated by exposure to Mg-containing solution. The possibility that the beta-action is potentiated by Mg ions which penetrated into the membrane is concluded.

Action Potentials↗
PubMed1978

Electrophysiological comparison between the longitudinal and circular muscles of the rat uterus during the estrous cycle and pregnancy.

The membrane activities of the longitudinal and circular muscles bundle of rat uteri were recorded with a single sucrose gap method, using animals at various stages of the estrous cycle, pregnancy and after ovariectomy. In the longitudinal muscle during estrus, an initial plateau potential was followed by a slow potential. During diestrus and metestrus, an asynchronized action potential composed of plateau and a slow potential were exhibited. The action potential recorded in uteri taken out of an ovariectomized animal or during early pregnancy was similar to that of uteri during diestrus and metestrus. The circular muscle during estrus gave a plateau potential similar to that of the longitudinal muscle. During diestrus, metestrus, early pregnancy and in the ovariectomized uterus, the membrane activity of the circular muscle was decomposed to produced small plateaus. The spike activity took place in the longitudinal muscle after mid-pregnancy. The slow potential was dominant in the circular muscle during mid-pregnancy, while spikes were progressively generated toward term. Those differences of membrane activity between the longitudinal and circular muscle bundles were discussed in relation to the endogenous change in the sex steroid hormones.

Action Potentials↗
PubMed1978

Effects of catecholamines on the circular muscle of rat myometria at term during pregnancy.

The effects of catecholamines on the circular muscle of myometria in pregnant rats at term (21st and 22nd days) were investigated by recording electrical and mechanical responses. Slow potentials were found to be the dominant activity in the morning on the 21st day of pregnancy, and spike potentials were manifested on the 22nd day. The alpha-excitation of catecholamines in the circular muscle was represented by mechanical potentiation, prolongation of the slow potential and depolarization of the membrane. In contrast, the beta-inhibition was mechanical inhibition, depression of the slow potential and hyperpolarization. Noradrenaline at a concentration of 6 X 10(-6M caused excitatory action in the circular muscle on the 21st day of pregnancy, while the effect became inhibitory on the 22nd day of pregnancy. Results obtained by the use of adrenergic agonists and antagonists led to the conclusion that the reversal of the effect of noradrenaline could be ascribed largely to the enhancement of the beta-action, the mechanism of which was brought about probably through the endogenous change in the steroid hormone secretion at the very end of pregnancy.

Action Potentials↗
PubMed1977

Effect of ions and drugs on the plateau potential in the circular muscle of pregnant rat myometrium.

Effect of Na, Ca, anions and isoprenaline on the plateau potential in circular muscle of 11- to 13-day pregnant rat myometrium were investigated using the double sucrose gap method. During the plateau potential, which amounted about 15-20 mV and lasted for 10-20 sec, the membrane conductance increased initially, then decreased. The amplitude and duration of the plateau potential increased by raising the external Ca concentration to between 0.3 and 3 mM, and decreased when the concentration was increased more. The plateau was prolonged in low Na solutin (54 mM). When 154 mM Cl was replaced with Br the plateau was prolonged, however, the plateau was nearly suppressed when Cl was replaced with benzene sulphonate or isethionate. Isoprenaline increased membrane conductance and depressed the plateau. It was concluded that a decrease in K conductance was largely responsible for the plateau potential, and an inward Ca current may have contributed to its formation.

Animals↗
PubMed1977

Effects of ions and drugs on the negative afterpotential in the longitudinal muscle of pregnant rat myometrium.

Effect of Na, Ca anions and drugs (isoprenaline, TEA, procaine) on the negative afterpotential in the longitudinal muscle of pregnant rat myometrium were investigated using the double sucrose gap method. The negative afterpotential having a peak amplitude of about 15 mV decayed initially rapidly then slowly, the total duration being about 1 sec. Raising the external Ca concentration up to 10 mM or reducing Na to 54 mM increased the amplitude of the negative afterpotential. Replacement of Cl with Br enhanced the negative afterpotential and and replacement with benzene sulphonate or isethionate depressed it. The application of 10 mM TEA increased, while 10 mM procaine reduced the amplitude of both spike and negative afterpotential. 10(-10)-107(-8)g/ml isoprenaline depressed the negative afterpotential dosedependently, while leaving the spike potential nearly unaffected. It was concluded that the negative afterpotential was composed of a least two ionic mechanisms, one of Cl origin, the other of Ca origin.

Animals↗
PubMed1976

Comparative investigations of alpha- and beta-effects on the longitudinal and circular muscles of the pregnant rat myometrium.

Comparative effects of noradrenaline (10(-8)-10(-6) g/ml) and isoprenaline (10(-10)-10(-6) g/ml) on electrical and contractile activity were investigated in longitudinal and circular muscle strips of rat myometrium (13-19 days pregnant). When recorded with an intracellular microelectrode, spike potentials of longitudinal muscle discharged spontaneously in bursts. Treatment with either noradrenaline or isoprenaline hyperpolarized the membrane and increased membrane conductance, causing the cessation of spontaneous activity. Slow potential was dominant in the circular muscle, and it became prolonged after treatment with noradrenaline, leading to an increase in tension. Isoprenaline reduced the duration of the slow potential and depressed the contraction. The minimal concentration of isoprenaline needed to suppress the spontaneous activity in circular muscle was much higher than in longitudinal muscle. The excitatory effect of noradrenaline on circular muscle was antagonized by treatment with phentolamine, and the inhibitory effect of catecholamines on both longitudinal and circular muscles by propranolol. alpha-Adrenoceptor appears predominant in circular muscle, while beta-adrenoceptor in longitudinal muscle in rat myometrium during late-pregnancy.

Action Potentials↗
PubMed1975

Physiological comparison of the longitudinal and circular muscles of the pregnant rat uterus.

A comparative investigation of the longitudinal and circular muscles in the pregnant rat uterus (10-15 days) was made by means of electrical and mechanical recordings. The response of the circular muscle strip was characterized in the following respects: application of stretch caused acceleration of spontaneous activity that was greater in extent than in the longitudinal muscle strip; tetanic contraction was not produced by repetitive stimuli in the range of 0.1-5 Hz; slow potential was dominant in the circular muscle cells. The longitudinal contraction of the uterine segment occurred in synchronization with the change in the intraluminal pressure. Either the longitudinal stretch or the increase in the intraluminal volume caused the acceleration of synchronized activity. Stimulation of the longitudinal muscle caused membrane response in the circular muscle cells and vice versa, suggesting electrical interference between longitudinal and circular muscle cells.

Animals↗
PubMed1975

Effects of magnesium and temperature during the recovery process from the potassium contracture of the pregnant rat myometrium.

Effects of external ions (Na, K, Mg) on the recovery from K-contracture of the pregnant rat myometrium were investigated in Ca-free media. Relaxation was faster, when the external concentration of Na and K ions was higher. The time course of relaxation within a limited range of 60-20% of the mechanical output followed a single exponential function. The rate of relaxation, given by the reciprocal of the period during which the contraction decayed to 1/e, was 0.3-0.5 min-1 at 34-35 degrees C in isotonic Na solution. Low temperature caused prolongation of the relaxation, and the activation energy estimated on the rate of relaxation was 3-4 kcal-mol-1. Relaxation became faster when Mg (0.5-20 mM) was added to the relaxation media. Relaxation in isotonic K media was slower than in isotonic Na media, and the addition of Mg caused a slight acceleration of the relaxation. Low temperature caused an acceleration of the relaxation, irrespective of the presence or absence of external Mg ions. In low K media, where K ions were replaced by isomolar sucrose, addition of Mg caused a significant acceleration of the relaxation. Activation energy ranged between 13-15 kcal mol-1 in the solutions containing Mg. This favors the existence of a relaxing system in pregnant rat myometrium that is Mg- and metabolism-linked.

Animals↗