Quick-release Method Research Articles

Series elasticity in the intact heart. Evidence for the application of the Hill model for muscle to the intact left ventricle.

Several recent studies have shown that the contractile state of the intact heart may be described by the instantaneous relationships between contractile element velocity, length and stress. However, there is little direct evidence that the intact heart can be described by a model containing at least a contractile element and a series elastic component (SEC). In isolated muscle the series elastic component can be analyzed by determining the length changes following quick releases to known loads during contraction. The characteristics of the effective SEC of the intact left ventricle (LV) were determined by a quick release method in 8 dogs in which the left ventricle contracted isovolumically against a balloon inserted via the mitral annulus. During active contraction, sequential withdrawals of 0.5 to 7.0 ml of fluid were performed rapidly (5-18 msec) by an electrically-timed, springloaded syringe. From these releases the calculated maximum extension of the SEC averaged 4.03 +/- 0.27% of LV circumference at LV pressures averaging 79/6 mmHg (systolic/end-diastolic; range 66-107/0-15 mmHg.) The reductions of the left ventricular midwall circumference were plotted against the corresponding changes in mean wall stress. The load extension curve determined in this manner was unchanged by varying the time of release and by norepinephrine infusion. These data support a model for the intact LV that contains an undamped SEC, the characteristics of which resemble those of isolated cardiac muscle.

The force-velocity relation in phasic contractions of venous smooth muscle.

The force-velocity relation of the rat portal vein has been studied during regular spontaneous contractions induced by elevated levels of [K-+]O AND [Ca-2+]o. No satisfactory description of the force-velocity relation was obtained by measuring shortening velocity in afterloaded isotonic contractions. Therefore the method of isotonic quick release was used, as this permits mechanical studies at specified instants of the contraction-relaxation cycle. The temporal development of the force-velocity relation in the phasic response was investigated. During a time interval in the rising phase of the contraction, at about the time for maximal dP/dt, the force-velicity curves were practically identical, suggesting a plateau in the intensity of active state. At later stages of the twitch the curves were progressively displaced towards the origin, the intercepts on both the force and the velocity axis becoming smaller. At the time of the isometric peak the maximal shortening velocity had declined relatively more than the isometric force. This is presumably caused by inhomogeneous activation of the muscle at the beginning of relaxation, The maximal force-velocity relation in the rising phase of the contraction can be described by Hill's (1938) equation with the following parameters (at 37 degrees tc): a/Po = 0.73 plus or minus 0.04, b = 0.54 plus or minus 0.04 lengths/s, Vmax = 0.74 plus or minus 0.02 lengths/s (n = 7, mean plus or minus S.E,). The force-velocity relation of the portal vein in comparison with other kinds of muscle is discussed.

Effect of stretching on the elastic characteristics and the contractile component of frog striated muscle.

1. The force-velocity relationship and the stress-strain curve of the so-called series elastic component (s.e.c.) of frog sartorius, semitendinosus and gastrocnemius have been determined during shortening against a given force (isotonic quick-release) and at high speed (controlled release): (a) from a state of isometric contraction and (b) after stretching of the contracted muscle. In both cases the muscle was released from the same length: this was usually slightly greater than the muscle's resting length.2. The muscle released immediately after being stretched is able to shorten against a constant force, P, equal to or even greater than the isometric force, P(0), at the same length. When the force P applied to the muscle is reduced below P(0) the velocity of shortening is greater after stretching, and the force-velocity curve is therefore shifted along the velocity axis: the shift is maximal when P is near to P(0) and it decreases rapidly with decreasing P.3. The extent of shortening of the s.e.c. required to make the force fall from P(0) to zero is 50-100% greater when the muscle is released immediately after stretching than when it is released from a state of isometric contraction. This difference is found by using either the controlled release method or the isotonic quick-release method.4. If a time interval is left between the end of stretching and the onset of shortening of the contracted muscle (controlled release method), the length change of the s.e.c., for a given fall of the force, is reduced and approaches that taking place when the muscle is released from a state of isometric contraction.5. Curare does not affect the results described above, indicating that these do not depend on modification of the neuromuscular transmission.6. It is concluded that stretching a contracted muscle modifies temporarily: (a) its elastic characteristics, as shown by the greater amount of mechanical energy released for a given fall of the force at the muscle's extremities, and (b) its contractile machinery, as it is suggested by the change of the force-velocity relationship.

Force-velocity and series elastic characteristics of smooth muscle from the hog carotid artery.

The force-velocity and series elastic characteristics of vascular strips from the media of hog carotid arteries were determined using the method of quick release to a known afterload. Shortening velocity was a function of load, and the data could be fitted by a rectangular hyperbola using the Hill equation, (P + a) V = b (P o - P), where P is the load, P o is the maximum isometric force developed at the optimum muscle length (L o ), V is velocity, and a and b are constants. The following dynamic constants were obtained for the electrically stimulated strips: estimated maximum shortening velocity for the unloaded muscle (V max ) = 0.12 L o /sec, b = 0.02 L o /sec, P o = 1.80 kg-wt/cm 2 = 1.76 x 10 6 dynes/cm 2 , and a/P o = 0.18. Maximum power output occurred at a load of 0.28 P o . The stress-strain curve for the series elastic component could be approximated by the simple exponential equation, stress = 0.034e 058 strain . The extension of the series elastic component at P o was 7.2% of L o .

Influence of extracellular calcium on isometric force and velocity of shortening in depolarized venous smooth muscle.

AbstractThe Ca++ dependence of the contracture response obtained in depolarized smooth muscle from rat portal vein was studied. Double reciprocal plots of isometric force versus [Ca++]n were examined by linear regression analysis for n = 1, 2 and 3. The data were consistent with a linear relationship for n = 2. This may be taken to indicate that isometric force is regulated by the binding of two calcium ions to an unknown “receptor compound” in the tissue. In other experiments the velocity of shortening was studied by the method of quick release after the muscles had developed isometric contractures in 2.5 or 0.4 mM [Ca++]0, respectively. The mean isometric forces elicited by these 2 levels of [Ca++]0 differed by a factor of 1.7, but the shortening velocities at comparable relative loads were essentially the same. These results may be considered in the light of recent studies of striated muscle which have been concerned with the problem whether Ca++ determines exclusively the number of activated cross bridges in the sliding filament system or whether it also influences the rate of movement of the individual cross bridge.

The Phasic and Tonic Contraction in the Longitudinal Muscle of the Earthworm

ABSTRACT In extension of preceding studies on the mechanical properties of the longitudinal muscle fibres of the earthworm, the phasic and tonic contractions were analysed under various conditions. The phasic contractions appeared on the tonic contraction which was maintained at a steady level by repetitive stimulation, and the tonic contraction decayed very slowly after cessation of stimulation. The length-tension curve indicated that the phasic and tonic contractions were both affected similarly by changing the muscle length. The mechanical ‘active state’ was investigated during the phasic and tonic contractions by means of the quick-release method. During the phasic contraction the ability to redevelop the tension was observed. During the early phase of the tonic contraction the muscle was in the ‘active state‘, but the tonic contraction continued even after the tension redevelopment had nearly ceased. The tonic contraction was absent when the temperature was raised to about 30 °C. 5-Hydroxytryptamine (2·5 × 10−6 M) decreased the tonic more than the phasic contraction. The tonic contraction disappeared completely in the presence of acetylcholine (5·5 × 10−4 M), while the phasic contraction was reduced but not abolished, λ-aminobutyric acid (10−8 to 5 × 10−4 M) had no effect on the contractions. Transition-metal ions suppressed mainly the phasic contraction in the order of Mn2+> Co2+ > Ni2+. The decrease in the phasic contraction was proportional to the logarithm of concentration of added divalent cations. The tonic contraction was also reduced but at higher concentration than the phasic contraction. It is postulated that, by depolarization produced by electrical stimulation or by acetylcholine, calcium ions are released from the plasma membrane and also from the sarcoplasmic reticulum. The phasic contraction might be generated mainly by calcium ions released from the membrane, and the tonic contraction might be caused mainly by calcium ions released from the sarcoplasmic reticulum.

Changes in the Action Potential and Contraction of Isolated Frog Muscle after Repetitive Stimulation

AbstractThe effect of repetitive stimulation of twitch fibres was studied in isolated whole muscle from Rana pipiens. Intracellular electrodes were used for recording membrane potentials, muscle tension was recorded isometrically and the decline of the active state of the contractile elements was determined by the quick release method. Repetitive stimulation caused an increase in the duration of the action potential and in the amplitude of the early negative after‐potential. To judge from experiments on fibres with disrupted transverse tubules, the increase in the duration of the action potential is due to changes in the surface membrane, while the increase in the amplitude of the after‐potential is related to the transverse tubules. The changes in the action potential and the after‐potential were independent of whether or not the muscle contracted and thus cannot be secondary to the contraction. The shape of the action potential and the after‐potential returned to normal within 5 min after stimulation at 10/sec for 60 sec while after 30 min there was still an increase in the peak twitch tension and a slower‐than‐normal decay of the active state in response to test shocks. This indicates that the post‐stimulatory potentiation is due to a prolonged active state which, in turn, is due mainly to causes other than changes in the action potential and after‐potential.

The series elastic component of frog gastrocnemius.

1. The force-extension curve of the series elastic elements of the frog gastrocnemius has been determined up to the force attained during stretching by means of the isotonic quick-release method, modified in order to allow the release of the muscle immediately after stretching.2. The series compliance decreases progressively up to a stress value of about 2 kg/cm(2) and then it remains constant up to the maximal values of stress attained (about 10 kg/cm(2)).3. The lengthening of the series elastic elements when the stress rises to its full isometric value (P(0)l(0)/M = 5.2 kg/cm(2)) is about 3% of the muscle resting length, l(0). The Young's modulus in the linear part of the diagram is 294 kg/cm(2).4. The elastic energy stored up to P(0) is on average 55 g cm/g; an additional amount of 63 g cm/g is stored during stretching the contracted muscle.

Active state in heart muscle. Its delayed onset and modification by inotropic agents.

The course of active state in heart muscle has been analyzed using a modified quick release method. The onset of maximum active state was found to be delayed, requiring 110-500 msec from time of stimulation, while the time to peak isometric tension required 250-650 msec. Further, the time from stimulation to peak tension was linearly related to the time required to establish maximum intensity of active state as well as to the duration of maximum active state. The duration of maximum active state was prolonged (90-220 msec), occupying most of the latter half of the rising phase of the isometric contraction. Norepinephrine (10(-5) M) shortened the latency from electrical stimulus to mechanical response, accelerated the onset of maximum active state, increased its intensity, decreased its duration, and accelerated its rate of decline. These changes were accompanied by an increase in the rate of tension development and the tension developed while the time from stimulation to peak isometric tension was abbreviated. Similar findings were shown for strophanthidin (1 microgram/ml) although lesser decrements in the duration of maximum active state and time to peak tension were found than with norepinephrine for similar increments in the maximum intensity of active state.

Series elasticity in heart muscle. Its relation to contractile element velocity and proposed muscle models.

The series elasticity (SE) of cat papillary muscle was measured in 6 muscles by the isotonic quick-release method, with careful correction for the compliance of the equipment. The resultant SE curve was exponential in form with an extension of 4% to 5% of initial muscle length for a preload of 0.5 g and a developed tension of 10 g; this demonstrates a stiffer SE for cardiac muscle than has previously been reported. The quick-release SE extension curve was unaffected by inotropic interventions or changing the time of quick release, and was less compliant than the SE curves calculated by two different isotonic methods. These differences arise from the fact that contractile element velocity has a secondary rise during the transition from the isometric to isotonic phase of any afterloaded contraction. With increasing preload (and initial muscle length) the SE became stiffer, suggesting that a substantial part of it is in series with both the contractile and parallel elastic elements.

Determination of the time course of the relaxing of the contractile element by the use of tension-frequency diagrams

By plotting the tension developed during maximal summation of muscle twitches against the stimulus interval, a curve can be drawn which has the same time course of the falling phase of the active state as determined by the method of quick release.

FROG FAST MUSCLE. II. A METHOD OF MEASURING INTERNAL SERIES COMPLIANCE.

ABSTRACT Methods which have been used in the past for estimating internal series compliance are discussed. A new method is described in which measurements of (a) rate of change of tension, and (b) speed of shortening are made in the isometric and isotonic phases respectively of a contraction containing a transition from one type of contraction to the other. If the mechanical power output of the muscle is assumed the same just before and just after the transition, the total series compliance can be obtained. The method is found to agree with Wilkie’s quick-release method, provided parallel elastic structures are not carrying significant tension at the transition.

Die abfallende Phase des aktiven Zustandes des Tibialis anterior, Gastrocnemius und Soleus der Katze und ihre Beeinflussung durch Dehnung und Sympathicomimetica

In einer vorausgehenden Arbeit (BLv, CK~A~~, Jv~~A u. RUM~]~Z 1963) wurde die Frage untersucht, ob die Dauer des Plateaus des aktiven Zustandes fur das charakteristische Verhalten eines tonischen und phasischen Skeletmuskels der Katze (Soleus und Tibialis anterior) bestimmend ist. Es zeigte sich, das die P]ateaudauer beider Muskeln nahezu gleich ist. Dieser Befund war nicht mit der Annahme in Einklang zu bringen, das die Verschmelzungsfrequenz eines Muskels von der Dauer des Plateaus allein abhangig sein soll. Auserdem lies sich keine Wirkung der Sympathicomimetica Adrenalin, Noradrenalin und Isoprenalin auf die Dauer des Plateaus des aktiven Zustandes beider Muskein nachweisen, obwohl die A_mine die Spannungsentwicklung der Einzelzuckung oder tetanischen Kontraktion beim Tibialis anterior steigern und beim Soleus vermindern (BowM~_¢~ u. Z)~MIS 1955, 1958; JVR~~t u. RV~M~T, 1962). Die sowohl fur die Verschmelzungsfrequenz als auch fur die Wirkung der Sympathicomimetica entscheidende Phase der Kontraktion der contractilen Elemente war demnach nicht die Dauer des Plateaus, sondern muste die abfallende Phase des aktiven Zustandes sein. Um die Richtigkeit dieser Schlusfolgerung direkt zu prufen, wurden Versuche mit der Methode der schnellen Entlastung (HILI~ 1953; RITCmE 1954; RITCmE u. W~Ya]~ 1955) zur Bestimmung der abfallenden Phase des aktiven Zustandes beim Tibialis anterior, Soleus und zum Vergleich auch beim Gastrocnemius durchgefuhrt. Dieser Methode zur Bestimmung des Verlaufes der abfallenden Phase liegt die ~berlegung zugrunde, das die Intensitat der Spannungsentwicklung der contractilen Elemente dann bestimmbar ist, wenn diese sich weder verkurzen noch verlangern, mit anderen Worten:wenn contraetile und elastische Elemente sich im Gleichgewicht befinden.