Effects of porcine relaxin on contraction, membrane response and cyclic AMP content in rat myometrium.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
T Osa
Publications and source records attributed to T Osa.
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↗
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↗
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↗
Comparative investigation of the electrical properties in myometrial longitudinal and circular muscles of rat during estrous cycle and pregnancy.
Explore the source record for details and available documents.
Action Potentials↗
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↗
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↗
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↗
Excitation-contraction coupling mechanism in visceral smooth muscle.
Explore the source record for details and available documents.
Animals↗
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↗
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↗
Electrophysiological and mechanical investigations on the dual action of prostaglandin E1 in the pregnant rat myometrium in vitro.
Effects of prostaglindin E1 (PGE1) on the myometrial activity of the pregnant rat were investigated by recording the contractile response and intracellular electrical activity. PGE1 (10-9--10-6 g/ml) caused a depression of the contractile activity in the fresh preparations of either longitudinal or circular muscle strip (within 2-5 hr after exposure to the artificial saline media). However neither membrane potential nor action potential was significantly affected by the treatment with the agents. By contrast, in the aged preparations (bathed in the saline media longer than 2-5 hr), an increase in the contractile response dose-dependently was caused. The generation of action potential was facilitated without depolarization of the membrane. The inhibitory response induced by PGE1 in the fresh preparation was converted to an excitatory response when treated with bretylium. The discussion covers the inhibitory effect of PGE1 which is mediated through intrauterine adrenergic system, and is perhaps due to the focal hyperpolarization block of the conduction of excitation. The excitatory effect is very likely caused by a direct action on myometrial cell membrane.
Animals↗
Effects of magnesium ion and temperature on the phasic and tonic contractions of the potassium contracture in the pregnant rat myometrium.
Effects of Mg ion, low temperature and 2,4-dinitrophenol on the Kcontracture were investigated in pregnant rat uteri. At 36-38degrees C, the addition of Mg ions increased the amplitude of tonic contraction when the isotonic K media contained 2.2 mM Ca (inhibitory effect). When the muscle strip was loaded with Mg ion by exposing it previously to a Locke-Ringer solution containing 1as nearly abolished but the inhibitory effect persisted. The amplitude of the tonic contraction was reduced, and the potentiating effect of the Mg ion was depressed at lower temperatures. The inhibitory effect persisted at low temperatures. The time course of relaxation of the phasic contraction consisted of two exponentials, the initial one fast and succeeding one slow. The effect of Mg on the relaxation during the initial phase was variable, butthe succeeding one always became slower when Mg ions were added. The initial phase of the relaxation became slower at lower temperatures. However, the succeding phase became faster. The above experimental results were interpreted to suggest that the sites of Mg action were two, one being at the outer surface of the membrane competing for occupation with Ca ions, and the other within or at the inner surface of the membrane regulating the amount of bound Ca which is in turn utilized to evoke contraction. The latter is probably mediated by metabolic processes.
Animals↗
Fluorescence and energy transfer of polypeptides containing naphthyl groups in their side chains.
Energy transfer in the singlet state was studied in solution at 25 degrees C for poly(beta-1-naphthylmethyl L-aspartate) and copolymers of beta-1-naphthylmethyl L-aspartate and gamma-benzyl L-glutamate. Transfer efficiencies, migration coefficients, migration lengths, and interaction radii were determined from the quenching studies using biacetyl as a quencher. The migration coefficient increases with increasing naphthyl groups in the copolymers. This means that singlet energy migrates among more naphthyl groups with increasing naphthyl groups in the polymer chain. Interaction radius for the fluorescence quenching by biacetyl was estimated to be in the range of 5.8 to 8.9 A irrespective of whether energy donor is monomer or excimer. Moreover, it was shown that energy migration via excimer does not take place and energy of the excimer is localized.
Aspartic Acid↗