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PubMed1976

Plastic properties of vertebrate smooth muscle (taenia coli of the guinea pig).

After extension and creep due to a constant load the taenia coli of the guinea pig shows plastic deformation. The deformation is partially abolished by complete unloading: to 51% in the relaxed and to 83% in the depolarized = contracted state. The quantitative relations between creep (N) and its time derivative (dN/dt) as well as those between stress relaxation (R) and dR/dt stated in our previous papers, remain valid if plastic deformations have occurred during these processes.

Animals↗
PubMed1978

Forelimb reflexes modulated by tonic neck positions in cats.

The modulation of monosynaptic forelimb reflexes by tonic neck positions was investigated in cats with the head fixed. Lateral flexion of the body in a horizontal plane markedly facilitates reflexes of the deep radial nerve (DR) in the ipsilateral forelimb, while the antagonistic ulnar nerve (ULN) reflexes are strongly inhibited. Opposite effects are seen after contralaternal body movement. Dorsiflexion of the body clearly increases DR-reflexes and exerts a reciprocal although more pronounced inhibition on ULN reflexes. Opposite effects appear after ventriflexion. The reflex modulation starts with head-body displacements of approximately 5 degrees and increases with increasing angles. Furthermore reflex modulation does not depend on the intact cerebrum and cerebellum. The comparison of forelimb and hindlimb reflexes shows a decrease of the neck influences along the spinal cord.

Animals↗
PubMed1978

CO2-dependent component of the neurogenic vascular tone in the cat.

Complete vascular isolation of the hindlimbs was performed in vagotomized cats under Sodium Pentobarbital anesthesia. The hindlimbs were perfused at constant flow with blood kept at a constant and physiological PO2, PCO2, and pH values by means of a specially designed pump-oxygenator system. The animals were hyperventilated with different CO2 mixtures (0%, 5%, 7% and 10% in O2) thereby changing blood gases and pH levels in the upper body but not in the hindlimb vascular bed. At body PaCO2 (mm Hg) of 13.7 +/- 1.0 (means +/- SE), 30.6 +/- 1.05, 40,4 +/- 0,9 and 58.4 +/- 2.9 the hindlimb perfusion pressure (mm Hg) was, respectively 124 +/- 7.6, 138 +/- 7.4, 156 +/- 11.9 and 187 +/- 15.1. These changes in perfusion pressure were still present after complete peripheral chemoreceptor denervation but were abolished after section of the spinal cord at the T5 level. Since hindlimb perfusion pressure fell when body PaCO2 was lowered below physiological levels it is concluded that part of the neurogenic vascular tone of the hindlimbs is maintained by a CO2 mediated stimulation of supraspinal structures.

Animals↗
PubMed1982

The contribution of the parallel and series elastic components to the dynamic properties of the rat tail artery under two different smooth muscle tones.

The dynamic elastic modulus (Ed) and the coefficient of wall viscosity (eta w) of the tail artery of normotensive rats were determined as functions of the circumferential wall stress under quasistatic and dynamic conditions. The experiments were performed under strong smooth muscle activation induced by norepinephrine, and during relaxation induced by papaverine. The following results were obtained. 1. Ed and eta w increase with increasing wall stress. At a given wall stress, Ed is virtually independent of frequency while eta w decreases markedly with increasing frequency. This behaviour of eta w is called thixotropy or pseudoplasticity. 2. In the wall stress range from 5--60 kPa the values of Ed, and in the wall stress range from 60--140 kPa those of eta w obtained under smooth muscle activation and during relaxation are virtually identical. 3. In the relaxed smooth muscle, the phase angles between sinusoidal pressure and radius changes area virtually independent of the mean wall stress at all frequencies. In the low stress range, the phase angles are greater at low frequencies in the activated state than in the relaxed state, decrease with increasing wall stress, and are virtually identical to the values under papaverine at high wall stresses. At high frequencies no dependence of the phase angles on the mean wall stress can be seen.

Animals↗
PubMed1984

Superfast tension transients from intact muscle fibres.

We have measured tension transients from tetanically stimulated intact single fibres of the M. lumbricalus and the M. tibialis anterior of the frog. The measurements were carried out between 5.5 and 7 degrees C at a sarcomere length of 2.1 and 3.1 micron with a displacement servo system capable of performing displacements of 50 micron in 40 microseconds. We found a very fast recovery process in the tension transients thus obtained and quantified the speed of the observed recovery process in terms of elasticity and damping. If a ramp-shaped input signal of 150 microseconds duration is applied to the system, the velocity is constant over about 100 microseconds. This property of the system enables us to study the velocity-dependent part of the initial drop in tension in more detail. The first part of the tension transients thus obtained, show three phases: an initial rapid drop in tension, a slower steady decrease in tension and a rapid recovery (30 microseconds).

Animals↗
PubMed1987

MgADP- increases maximum tension and Ca2+ sensitivity in skinned rabbit soleus fibers.

Increasing concentrations of MgADP- or MgCDP- in the millimolar range cause an increase in the maximum Ca2+ -activated tension that a skinned rabbit soleus muscle fiber can develop in the presence of 2 mM MgATP2- or MgCTP2- respectively. In contrast, the maximal Ca2+ -activated ATPase activity of the fiber decreases in the presence of MgADP-. As the nucleoside diphosphate (MgADP- or MgCDP-) concentration is increased, the Ca2+ concentration required for half-maximal activation of tension is reduced. MgADP- has a similar effect on the Ca2+ concentration required to half-maximally activate the fiber ATPase. The effects on tension are due to magnesium nucleoside diphosphate and not some other form of nucleoside diphosphate since the effects occur at both low (pMg 4) and control (pMg 3) Mg2+ concentrations. Cooperativity, as judged by the Hill "n" value relating isometric tension and Ca2+, is less in the presence of 5 mM MgADP- as compared to a control (no added MgADP-) "n" value. Increasing concentrations of inorganic phosphate (Pi) in the millimolar range decrease maximum Ca2+ -activated tension, and increase the concentration of Ca2+ required to half-maximally activate tension, effects opposite to those of MgADP. These data are consistent with the hypothesis that cooperative interactions between actin and myosin can affect the affinity of troponin for Ca2+.

Adenosine Diphosphate↗
PubMed1981

The influence of temperature on the isometric characteristics of fast and slow muscle in the cat.

The maximum tetanic tension (initial strength) and the length of time, 20, 40 or 60%, of that initial strength could be maintained (endurance) was assessed in 2 fast twitch muscles (the plantaris and the medial gastrocnemius) and a slow twitch muscle (the soleus) of the cat at muscle temperatures ranging between 22 and 38 degrees C. The results of these experiments showed that the strength of the soleus was constant between muscle temperatures of 38 to 28 degrees C, and then gradually decreased as the muscle was cooled further. Plantaris, on the other hand, showed a reduction in strength at all muscle temperatures less than 38 degrees C; the response of the medial gastrocnemius was between these two extremes. The longest endurance for the soleus muscle was found to be at a muscle temperature of 28 degrees C, the endurance being as much as 3 times higher at this temperature than at muscle temperatures of 22 or 38 degrees C. The medial gastrocnemius showed a similar response but the endurance only doubled when comparing the endurance at a muscle temperature of 28 to 38 degrees C. In contrast, the plantaris maintained a constant endurance over the temperature range of 38 to 28 degrees C; below this muscle temperature the endurance decreased markedly. The mechanism for this response appeared to be related to the effect of temperature on the contractile characteristics of the muscles.

Animals↗
PubMed1982

Length dependence of calcium activated isometric force and immediate stiffness in living and glycerol extracted vascular smooth muscle.

Vascular smooth muscle series elasticity was examined in living and glycerinated preparations as a function of the tissue length or calcium elicited force. Isometrically contracted smooth muscle strips were submitted to small quick stretches and releases (rise time 1.5 ms). The resulting immediate tension changes were proportion to the length changes for length steps ranging from -0.5% L0 to +2% L0. Plotting the immediate tension changes versus the length steps resulted in force-extension diagrams of the series elasticity (T1-curves). The linear parts of the T1-curves extrapolated to a common abscissa intercept of about -1% to -2% L0 irrespective of the tissue length or the degree of calcium activated force. The slopes of the T1-curves taken as the stiffness of the series elasticity increased in proportion to the isometric tension and depended on the tissue length or the degree of calcium activation in a similar way as tension. It is concluded that tension changes due to changes in the calcium concentration or the tissue length are caused by a change in the number of attached crossbridges. Results obtained in "skinned" fibres were similar to the one obtained in living fibres indicating that electromechanical coupling was not a major factor in determining the decrease in isometric tension and stiffness at short lengths.

Adenosine Triphosphate↗
PubMed1982

Electrical and mechanical properties and neuro-effector transmission in the smooth muscle layer of the guinea-pig ileocecal junction.

Electrical and mechanical properties and neuroeffector transmission were studied in circular strips of smooth muscle taken from the ileocecal junction of guinea-pigs in relation to sphincter action, using the microelectrode, and tension recording methods. The membrane potential of the smooth muscle was low (-43mV) compared with the membrane potential of circular muscle cells of the ileum or caecum (-58 mV or 62 mV). Only small populations of the muscle cells (about 5%) generated spontaneous action potentials. Field stimulation of the tissue produced an initial slight relaxation followed by a contraction, and the mechanical responses were accompanied by membrane hyperpolarization (i.j.p.) followed by repolarization with rebound spikes. Treatment with atropine increased the amplitude of i.j.p.s and decreased the amplitude of the rebound repolarization. Propranolol or phentolamine did not affect the amplitude of i.j.p., however, phentolamine slightly reduced the amplitude of the rebound repolarization. These results indicate that the ileocecal junction is predominantly controlled by non-adrenergic, non-cholinergic inhibitory nerve fibres and that the distribution of adrenergic and cholinergic excitatory nerve fibres is sparse.

Animals↗
PubMed1975

Tonic properties of the Flexor carpi radialis muscle of the male frog (Rana temporaria).

The mechanical acitvity of the isolated flexor carpi radialis muscle (FCRM) of the mature male frog (Rana temporaria) was compared to that of the sartorius muscle. Muscles were stimulated directly by massive shocks at 20 degrees C and isometric tension was recorded during single twitch, twitch series, long tetani and long tetanus series. Some groups of muscles were poisoned with IAA-N2 or FDNB. The FCRM showed a high resistance to fatigue during a tetanus series and a "fatigue contracture" during a twitch series. The rate of the tetanic tension rise was smaller by five to six times than in the sartorius muscle (0 to 50% Po) and the twitch/tetanus ratio was always very small. During continuous activity and after the blocking of recovery metabolic pathways, FCRM used its energetic stores two to three times slower than the sartorius muscle. These stores did not seem to be more important. The results indicate that the FCRM is not a "tonic" muscle but, quite possibly, is composed of several types of fibre like many other frog muscles. However, some characteristics of mechanical response cannot be explained by the common classification into two types of fibre.

Animals↗
PubMed1984

The time course of changes in contraction kinetics during the tonic activation of the rat tracheal smooth muscle.

The tension increase after onset of electrical stimulation (30 Hz square wave; 1.65 ms pulse duration) and after the cessation of inhibiting length vibration (frequency 100 Hz sinus; amplitude 6% of the muscle length) was analysed in the isolated rat tracheal smooth muscle. In the first experimental series, tonic contraction was interrupted by a 2 s vibration applied 4-256 s after a preceding stimulation. In the second series, the onset of force development was delayed by a long-term vibration stopping 6-258 s after the commencement of a simultaneously performed electrical stimulation. In both the experimental series tested, the time course of post-vibration tension recovery showed an initial fast and a subsequent slow component. The former reflects the kinetics of cross-bridge reattachment and the latter those of the normal actin-myosin interaction cycle. The time constants of both these components reached a minimum of 0.58 +/- 0.04 s (fast) and 3.49 +/- 0.28 s (slow component) when the vibration stopped 18 s after the start of stimulation. Both values increased to 1.29 +/- 0.15 s and 9.98 +/- 1.17 s after a preceding stimulation of 256 s. These changes in the time constants may reflect the slowing of cross-bridge action under prolonged contraction. Such variations in the time constants of post-vibration tension recovery occurred without any corresponding changes in the steady state tension developed after cessation of vibration. These results lend further support to the supposition that different mechanisms might control the rate and extent of smooth muscle contraction.

Actins↗