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At least 1,387 records · Page 77Linked to original sources
PubMed1990

Differential regulation of smooth muscle contraction in rabbit internal anal sphincter by substance P and bombesin.

Substance P and bombesin induce contraction of isolated IAS smooth muscle cells by different intracellular mechanisms. The cells contracted in a dose dependent manner to both peptides. The kinetics of contraction were different. Substance P induced contraction peaked at 30 seconds and declined in a time dependent manner while bombesin induced contraction peaked at 30 seconds and was maintained for up to 8 minutes. The absence of extracellular calcium in the medium (0 calcium and 2 mM EGTA) had no affect on substance P induced contraction while it blocked bombesin induced contraction. Substance P induced contraction was blocked by the calmodulin antagonist W7 (10(-9)M) and was not affected by the PKC antagonist H7 (10(-6)M). Bombesin induced contraction was blocked by the PKC antagonist H7 and was not affected by the calmodulin antagonist W7. Our data indicate that substance P induces a transient contraction utilizing intracellular calcium and a calmodulin dependent pathway, while bombesin induces a sustained contraction utilizing calcium from extracellular sources and a calmodulin independent pathway.

Anal Canal↗
PubMed1992

Transient hyperpolarization of non-contracting muscle fibres in anaesthetized rats.

1. Following laminectomy, the L5 ventral roots of anaesthetized rats were split and approximately half of the nerve fibres were stimulated at 40 Hz. Resting membrane potentials were then measured in previously contracting and non-contracting soleus muscle fibres. 2. In the non-contracting soleus fibres there was a post-tetanic increase in mean resting potential (from -82.2 +/- 7.1 (S.D.) to -91.6 +/- 8.7 mV) which was similar to that in contracting fibres (from -83.02 +/- 6.1 to -91.3 +/- 7.3 mV). In both types of fibres the hyperpolarizing responses (HRs) were evidently due to increased sodium pump activity since they could be abolished by the addition of ouabain (1 x 10(-4) M) to the bathing fluid. 3. The beta-adrenergic antagonist, propranolol, completely suppressed HRs in the non-contracting fibres and produced moderate reductions in the contracting ones. The alpha-adrenergic blocking agent, phentolamine, had no effect on the contracting fibres and only a modest, inhibitory, one on the non-contracting fibres. 4. On the basis of the above drug actions it appeared that catecholamines were necessary for the full development of HRs in contracting and non-contracting fibres; noradrenaline, released from intramuscular sympathetic nerve endings, may have been involved. 5. The increased sodium pump activity in the non-contracting fibres would serve to moderate the rise in interstitial [K+] caused by K+ efflux from the contracting fibres. By preventing passive depolarization, due to the rise in interstitial [K+], the sodium pump would also maintain the availability of non-contracting fibres for subsequent recruitment.

Animals↗
PubMed1999

Calcium ions modulate regulation of smooth muscle contraction mediated by phosphorylation of myosin regulatory light chains.

The effect of calcium ions on conformational changes of F-actin initiated by decoration of thin filaments with phosphorylated and dephosphorylated heavy meromyosin from smooth muscles was studied by fluorescence polarization spectroscopy. It is shown that heavy meromyosin with phosphorylated regulatory light chains (pHMM) promotes structural changes of F-actin which are typical for the "strong" binding of actin to the myosin heads. Heavy meromyosin with dephosphorylated regulatory light chains (dpHMM) causes conformational changes of F-actin which are typical for the "weak" binding of actin to the myosin heads. The presence of calcium enhances the pHMM effect and attenuates the dpHMM effect. We propose that a Ca2+-dependent mechanism exists in smooth muscles which modulates the regulation of actin--myosin interaction occurring via phosphorylation of myosin regulatory light chains.

Actins↗
PubMed1997

Oxygen uptake in maximally contracting muscle perfused at low flow with high O2 affinity erythrocytes.

To analyze the roles of blood flow and blood-tissue diffusion in determining oxygen (O2) availability to maximally exercising skeletal muscle, we investigated the influence of low flow on the O2 uptake (VO2)-venous PO2 (PVO2) relation with normal and high O2 affinity erythrocytes. We prepared normal and high O2 affinity erythrocytes by incubating human citrate-phosphate-dextrose-stored erythrocytes with and without cyanate. We perfused maximally contracting gastrocnemius muscle at 4-Hz isometric twitch with solutions containing normal and high O2 affinity erythrocytes for 3 min in anesthetized dogs. During stimulation, perfusion flow was maintained low at 50 ml.min-1.100 g-1 with a perfusion pressure of 50 mmHg. PVO2 for normal affinity erythrocytes (25.6 Torr) was significantly (p < 0.05) higher than that for high O2 affinity erythrocytes (15.9 Torr). Nevertheless, the VO2 for normal and high O2 affinity erythrocytes was approximately the same value, 6.5 ml.min-1.100 g-1 (p > 0.05). The O2 extraction rate was approximately 80% in normal and high O2 affinity erythrocytes. These results indicate that VO2 at low flow was independent of PVO2 in maximally contracting skeletal muscle, although PVO2 was reversely correlated with O2 affinity. We suggest that this PVO2-independency of VO2 at low flow is caused by long red-cell transit time in the capillary without diffusion-limitation and/or a 20% constant arterio-venous shunt of arterial O2 delivery.

Animals↗
PubMed1984

The inhibitory effect of X537A on vascular and intestinal smooth muscle contraction.

The effects of X537A (Lasalocid) on contractions induced in vascular and intestinal smooth muscles were examined. High K-induced sustained contractions were inhibited by X537A with an IC50 of 2.8 X 10(-6) M in rabbit aorta and 8.8 X 10(-8) M in guinea-pig Taenia coli. Changing the Ca concentration in the medium did not modify the effect of X537A. X537A also inhibited the noradrenaline-induced contraction in aorta (IC50 = 7.0 X 10(-8) M). In a solution without added glucose, the inhibitory effect of X537A on the K-induced contraction in aorta was augmented (IC50 = 1.5 X 10(-8) M). Under hypoxic conditions, the inhibitory effects of X537A on the noradrenaline-induced contractions in aorta and on the K-induced contraction in T. coli were decreased (IC50 greater than 10(-5) M and 3.2 X 10(-6) M, respectively). X537A inhibited the K-induced increase in cellular 45Ca content in aorta measured by a modified lanthanum method. However, the IC50 for 45Ca uptake (6.6 X 10(-7) M) was lower than that for K-induced contraction. In both tissues, X537A decreased the ATP content. Oxygen consumption of rat liver mitochondria was inhibited by X537A. From these results, it is concluded that the inhibitory effect of X537A on the noradrenaline-induced contraction in aorta and the K-induced contraction in T. coli, but not the K-induced contractions in aorta, may be due to the inhibition of aerobic metabolism.

Adenosine Triphosphate↗
PubMed1991

Defect in colonic smooth muscle contraction in patients with ulcerative colitis.

Patients with ulcerative colitis have decreased postprandial colonic contractions. The purpose of this study was to determine whether the smooth muscle from patients with ulcerative colitis responds abnormally in vitro to different stimuli. Circular colonic smooth muscle strips from patients with ulcerative colitis, acute diverticular disease, or adenocarcinoma were stretched to the optimal length and stimulated with electrical field stimulation (EFS), bethanechol, or increased concentrations of extracellular K+. The EFS-stimulated on-contraction was similar in each group, but the off-contraction was decreased in patients with colitis compared with patients with cancer (P less than 0.02) or diverticular disease (P less than 0.01). Bethanechol stimulated a dose-dependent colonic contraction, which was less in the strips from patients with colitis compared with cancer (P less than 0.02) or diverticular disease (P less than 0.05). The response to increased extracellular K+ was less in muscle from patients with colitis (P less than 0.01) than in the other tissues. Muscle from diverticular disease developed greater stress to K+ stimulation than did muscle from cancer (P less than 0.05). These studies suggest that there is a decrease in the force of muscle contraction in colonic muscle obtained from patients with colitis compared with normal muscle resected from patients with cancer or with muscle associated with diverticular disease of the colon. The similar relatively low amplitude of the on-contraction in each group suggests the physiological release of an inhibitory neurotransmitter.

Adenocarcinoma↗
PubMedDate not supplied

Comparative investigations of aspirin and indomethacin effects on blood flow in the vascular bed of skeletal muscles at rest and during muscle contractions in dogs and cats.

The effecs of two different inhibitors of prostaglandin synthesis--aspirin and indomethacin--on the blood flow in the vascular bed of the hindleg of vagotomized animals were studied before, during and after muscular activity of this limb. The responses of resistance and capacitance vessels were recorded simultaneously. Muscular contractions were evoked stimulating electrically (4 impulses/second) the peripheral part of the sciatic nerve. It was found that both inhibitors reduced exercise hyperaemia and postexercise hyperaemia. The response of the capacitance vessels was also reduced during muscular contractions. The obtained results confirmed that endogenous prostaglandins participate in the vascular response during exercise in the precapillary and postcapillary sections of microcirculation in the muscles. The particularly important effect of aspirin on postexercise hyperaemia in dogs in relation to cats is stressed.

Animals↗