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Results for “Muscle Tonus”

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At least 397 records · Page 22Linked to original sources
PubMed1980

Effects of increasing osmolality on rat ileal smooth muscle.

The effects of changing bathing medium osmolality on tension generation in smooth muscle were studied on potassium-depolarized segments of rat ileum. Increasing the tonicity of the medium evokes a transient relaxation of the smooth muscle; restoration of isotonicity evokes a transient contraction of similar amplitude and time course. While immersed in hypertonic media of less than 1.3 times normal tonicity, the smooth muscle slowly increases its isometric tension; in media of nearly twice normal tonicity, the smooth muscle loses tension. All of these effects occur whether the medium is made hypertonic with added NaCl or sucrose.

Animals↗
PubMed1976

The dilatatory action of adenosine on pial arteries of cats and its inhibition by theophylline.

The effect of adenosine upon pial resistance vessels was studied using local microapplication from the perivascular side and measurement of vascular diameter. Concentration-response curves revealed a concentration-dependent dilatatory effect of adenosine between 10(-7) and 10(-3) M. The degree of dilatation was independent of initial vessel size (47-260 mu). The dilatations due to adenosine could be reduced by theophylline in a reversible competitive antagonism. Concentration-response curves for theophylline yielded no vascular reaction at concentrations of up to 10(-5) M theophylline. From these data is is concluded that the pial arterial resting tone is not influenced under our experimental conditions by adenosine formed and released by brain tissue. The dilatations measured at high theophylline concentrations are apparently due to a mechanism different from the adenosine antagonism.

Adenosine↗
PubMed1980

Effects of a mild weight-lifting program on the progress of glucocorticoid-induced atrophy in rat hindlimb muscles.

The effect of a mild weight-lifting program on the progress of glucocorticoid-induced atrophy was investigated. Groups of rats were either injected daily for 6 weeks with triamcinolone acetonide, 1 mg/kg (group S), subjected to a weight-lifting program 4 times per week (group T), or subjected to the injection and weight-lifting programs concurrently (group ST). The training program, besides decreasing the normal body weight gain of control (group C) rats, had no effects on gastrocnemius and soleus muscles. In group ST, the extent of gastrocnemius atrophy was less severe than in group S, and the mean areas of all fiber types were greater in similar proportion. Gastrocnemius muscles were also tetanically stronger (g, g/g body weight) in group ST than group S. The soleus muscles of groups ST and S were similar in all indices of size and strength, except for a significantly decreased fast-twitsch-oxidative-glycolytic (FOG) mean fiber area in the ST seleus muscles. The extent of fast-twitsch muscle atrophy resulting from chronic glucocorticoid treatment can be lessened by mild weight-lifting exercise. Differences in fiber area responses between soleus and gastrocnemius may reflect recruitment and/or metabolic differences of similar fiber types in the two muscles.

Animals↗
PubMed1983

Alterations in smooth muscle contraction kinetics during tonic activation.

The kinetics of actin myosin interaction were studied in rat tracheal smooth muscle by analyzing the time course of post-vibration tension recovery. Longitudinal vibration (100 Hz sinus: 8% of the muscle length) of the contracted preparation (electrical field stimulation 30 Hz, 0.3 ms or 0.1 mM acetylcholine treatment) inhibits the process of force generation. The tension recovery after cessation of vibration follows a double exponential function with an initial fast and a subsequent slow component (the time constants averaged 1.17 +/- 0.10 s and 7.0 +/- 0.32 s (n = 60), respectively). Changes in the amplitude of vibration, the stimulation strength, or the extent of resting tension affect the amplitude without altering the time constants of tension recovery. These experimental conditions influence rather the number than the kinetics of acting cross-bridges. An extension of the pre-vibration stimulation period from 15 s to 16 min as well as a reduction in temperature from 37 degrees C to 25 degrees C hardly affects the extent of force development. However, the time constants of both the fast and the slow component of tension recovery were increased by up to a factor of about 7. These experimental results indicate an effect on the kinetics of actin myosin interaction.

Actins↗
PubMed1983

Changes of steady state activity in motor cortex consistent with the length-tension relation of muscle.

Steady state activity of motor cortex (MI) neurons and muscles was examined in relation to joint position. Two monkeys performed either isometric or load-bearing isotonic contractions, at different joint positions and during variation of steady torque. In either condition, MI steady state firing rate were found to be related to the amount of muscular excitation necessary to adjust muscle tension to length at any given position and load. The results obtained from 526 neurons (including pyramidal tract neurons) demonstrate for 206 neurons a correlate of the length-tension relation of muscle in the motor cortex.

Animals↗
PubMed1985

Avian adductor profundus muscle: characterization of a pure slow tonic region by histochemical, monoclonal antibody and peptide mapping studies.

The fibre type composition of the avian adductor profundus (AP) muscle which is composed of a thick white posterior part (Post. AP) and a thin red anterior part (Ant. AP) was investigated. Using the histochemical ATPase technique, monoclonal antibody analysis of myosin and C-protein isoforms, and electrophoretic and peptide mapping analyses of myosin, we have established that the Post. AP is composed of essentially pure slow tonic fibres similar to those of the anterior latissimus dorsi muscle (ALD). The Ant. AP, on the other hand, is shown to contain a mixture of slow and fast fibres, the latter giving immunocytochemical reactions atypical of the fast fibres. The larger size of the Post. AP in comparison with the ALD muscle should provide significantly more tissue for biochemical studies of tonic fibres than was previously available.

Adenosine Triphosphatases↗
PubMed1995

Nitric oxide and endothelin in pathophysiological settings.

The role of the endothelium is now known to encompass the generation of many potent cytokines which impact endothelial cells, adjacent tissue such as smooth muscle cells, and distant sites in an autocrine, paracrine, and endocrine manner, respectively. This review addresses two of these cytokines, nitric oxide and endothelin, and describes how each effects the functions of endothelial cells, including regulation of platelet aggregation and coagulation, regulation of vasomotor tone, modulation of inflammation, and the regulation of cellular proliferation. The emphasis is on the increasingly recognized importance of the autocrine and paracrine mechanisms by which nitric oxide and endothelin act. In particular, autoinduction of endothelin is proposed as a central mechanism underlying endothelin's renowned effects. Additionally, specific nitric oxide/endothelin interactions are discussed by which each cytokine modulates the production and actions of the other. The net effect observed in a variety of physiological and pathophysiological settings, therefore, reflects a balance of these opposing functions.

Cell Division↗