Search results for "Muscle Contraction"

Synthesis and Muscarinic Activity of Isoxazole-substituted 1,2,5,6-Tetrahydropyridines

1994

Selective action of two aporphines at alpha 1-adrenoceptors and potential-operated Ca2+ channels.

1993

Abstract Contractions evoked by noradrenaline (1 μM) or a depolarizing solution of 60 mM KCI were concentration dependently depressed by the aporphine alkaloids (S)-boldine and (R)-apomorphine in rataorta. Both drugs had a greater inhibitory potency on the contraction elicited by noradrenaline. Dose-response curves for noradrenaline were shifted to the right in presence of (S)-boldine. (R)-Apomorphine acted by a complex mechanism at α 1 -adrenoceptors and its inhibitory effects was irreversible. The conformational features of these alkaloids may explain their different behaviour at α 1 -adrenoceptors. In Ca 2+ -free solution, the alkaloids inhibited the contraction evoked by noradrenaline b…

Multiple actions of glaucine on cyclic nucleotide phosphodiesterases, α1-adrenoceptor and benzothiazepine binding site at the calcium channel

1992

1. In the present study, the properties of glaucine (an aporphine structurally related to papaverine) were compared with those of papaverine, diltiazem, nifedipine and prazosin. The work includes functional studies on rat isolated aorta contracted with noradrenaline, caffeine or KCl, and a determination of the affinity of glaucine at calcium channel binding sites of alpha-adrenoceptors, by use of [3H]-(+)-cis-diltiazem, [3H]-nitrendipine and [3H]-prazosin binding to cerebral cortical membranes. The effects of glaucine on the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta were also determined. 2. Contraction evoked by noradrenaline (1 micro…

Investigations of the dual contractile/relaxant properties showed by antioquine in rat aorta.

1993

1. In the present study we assessed the activity of antioquine, a bisbenzyltetrahydroisoquinoline alkaloid isolated from Pseudoxandra sclerocarpa, by examining its effects on the contractile activity of rat isolated aorta, specific binding of [3H]-(+)-cis-diltiazem, [3H]-nitrendipine and [3H]-prazosin to cerebral cortical membranes and the different molecular forms of cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta. 2. Contractions in rat aorta induced by high concentrations of KCl (80 mM) and noradrenaline (1 microM) were inhibited by antioquine in a concentration-dependent manner (0.1 microM- 300 microM). The alkaloid appeared more potent against KCl-induced contract…

Signal Characteristics of EMG with Special Reference to Reproducibility of Measurements

1975

Reliability and constancy of recordings of EMG signal characteristics were investigated from the measurements taken with miniature size surface electrodes during submaximal and maximal contraction of the rectus femoris muscle. The following EMG variables were studied: integrated EMG (IEMG) various bandwidths of the power spectral density function, mean power frequency (MPF), and rise time, amplitude and number of spikes of the averaged motor unit potential (AMUP). The results indicated that for most of the variables studied the reproducibility of measurements was better within the test session (reliability) than between the different test days (constancy). The reliability values for IEMG, M…

Effects of 5-HT4 receptor stimulation on basal and electrically evoked release of acetylcholine from guinea-pig myenteric plexus

1992

The effects of 5-methoxytryptamine and 5-hydroxytryptamine (5-HT) on both basal and electrically evoked outflow of tritium were studied in guinea-pig myenteric plexus preparations preincubated with [3H]-choline. Basal outflow. 5-Methoxytryptamine caused a transient and calcium-dependent increase in basal outflow of [3H]acetylcholine that was abolished by tetrodotoxin. Ondansetron (1 μmol/1) did not affect the stimulatory response of 5-methoxytryptamine but ICS 205-930 (1 and 3 μmol/1) produced parallel rightward displacements of the concentration-response curve to 5-methoxytryptamine. The PKB value for ICS 205-930 was 6.6 suggesting an involvement of 5-HT4 receptors. 5-HT caused an increase…

Two types of receptors for 5-hydroxytryptamine on the cholinergic nerves of the guinea-pig myenteric plexus

1985

Abstract The effects of 5-hydroxytryptamine (5-HT) on spontaneous and electrically-evoked release of [3H]-acetylcholine (ACh) from guinea-pig myenteric plexus preparations preincubated with [3H]-choline have been investigated in the absence of cholinesterase inhibitors. 5-HT caused a transient increase in spontaneous release and an inhibition of the electrically-evoked release of [3H]-ACh. The 5-HT-induced contractions of the longitudinal muscle were clearly related to the increase in spontaneous release. The inhibitory effect was not due to activation of alpha-adrenoceptors since it was also observed in the presence of tolazoline and on strips from reserpine-pretreated guinea-pigs. After d…

Participation of Intracellular Calcium Stores in Serotonin-Induced Contractions in Rat Aorta

1993

Serotonin 1 mumol/l induces a contractile response in the isolated rat aorta in both the presence or absence of extracellular Ca. The present study analyzes the influence of temperature and caffeine on subsequent serotonin-induced contractions. In Ca-free medium, the contraction elicited by serotonin was higher at 25 degrees C than at 37 degrees C. In addition, the existence of two independent intracellular Ca pools releasable by serotonin, one of them also sensitive to caffeine, is postulated. The results also showed that addition of serotonin decreases the contractile response to this agonist in Ca-free medium.

Amplifying effect of serotonin on contractile responses in rat aorta and depletion of intracellular Ca-stores

1993

1. Serotonin, 1 microM, induces a contractile response in isolated rat aorta in the presence or absence of extracellular Ca. 2. In Ca-free media, the fast phasic contraction is lower in magnitude and further addition of serotonin evokes no response. 3. Recovery of the contractile response in Ca-free medium is obtained by a 40 min incubation in Ca-containing solution. 4. In Ca, Mg-free medium, the response to serotonin is significantly higher than that obtained in the presence of Mg. 5. An amplifying effect of serotonin on the contractile responses induced by serotonin itself or by noradrenaline was observed in Ca-containing but not in Ca-free solution.

Effects of different unstable supports on EMG activity and balance

2013

This study analysed the equilibrium strategies and EMG activity during postural equilibrium in four different unstable surfaces. Thirteen team sport males were tested on a FLAT surface and on three different wobble boards (JAKOBS(®) with easy multidirectional displacements, FREEMAN with strong multidirectional displacements and LATERAL with unidirectional lateral displacements). They had to maintain single-limb stance during 5s for each condition. The right foot centre of pressure (COP) position and its variability with concomitant EMG activity of soleus (SOL), tibialis anterior (TA), peroneus longus (PL) and extensor digitorum longus (EXD) muscles were recorded. Subjects maintained balance…