Isometric relaxation in rat myocardium: Load dependence and influence of caffeine

Poggesi, Corrado; Ricciardi, L; Reggiani, Carlo; Minelli, R

doi:10.1007/bf01953225

Cited by 7 publications

(5 citation statements)

References 12 publications

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“…Moreover, relaxation has recently been shown to be sensitive to the level of external load in both mammalian heart muscle (Brutsaert et al, 1978b(Brutsaert et al, , 1980 and in spontaneously beating single cardiac cells (Lecarpentier et al, 1979) in which the sarcoplasmic reticulum was still functional. Intracellular calcium-sequestering systems, particularly the sarcoplasmic reticulum, have been assumed to account partially for this property, which disappears in mammalian heart muscle treated with caffeine (Lecarpentier et al, 1979;Poggesi et al, 1979), and which is not observed in frog myocardium (Brutsaert et al, 1978b). The present study extends these observations by examining sarcomere kinetics during cardiac relaxation, in both "isotonic* and 'isometric* contractions, and demonstrates that two mechanisms are involved during cardiac relaxation.…”

supporting

confidence: 54%

“…3, March 1985al., 1978a, which destroys both sarcolemma and sarcoplasmic reticulum (Orentlicher et al, 1974;Fabiato and Fabiato, 1975). Load sensitivity also disappears in a caffeine medium (Lecarpentier et al, 1979;Poggesi et al, 1979) which partially inhibits the sarcoplasmic reticulum (Weber and Herz, 1968). Furthermore, load sensitivity of relaxation is not observed in the frog ventricular strip (Brutsaert et al, 1978b) where the sarcoplasmic reticulum is scarcely developed (Staley and Benson, 1968), nor in newborn rat myocardium (personal observation) in which the sarcoplasmic reticulum is not yet functional (Fabiato and Fabiato, 1978).…”

Section: Time Course Of Sarcomere Relaxation Occurring In Two Phasesmentioning

confidence: 81%

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Real-time kinetics of sarcomere relaxation by laser diffraction.

Lecarpentier¹,

Martin²,

Claes³

et al. 1985

Circulation Research

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Kinetics of sarcomere movement were studied in real-time by laser diffraction. Instantaneous sarcomere shortening was measured during afterloaded twitches simultaneously with instantaneous shortening and tension of the whole trabecula excised from rat right ventricle. Resting sarcomere length at optimal length was 2.20 +/- 0.02 micron (mean +/- SEM). Maximum amplitude of sarcomere shortening was 0.30 +/- 0.01 and 0.16 +/- 0.01 micron, respectively, in twitches loaded with preload only, and in "isometric" twitches. When the isotonic load (expressed as a percentage of maximum isometric force TF) increased, the maximum velocity of sarcomere relaxation max Vr (micron/sec) decreased: max Vr = -4 exp (-2.5 X 10(-2) % TF); r = 0.95. The time course of sarcomere relaxation appeared to be progressively delayed when the total load increased from preload only up to "isometric" load. Sarcomere relaxation occurred in two successive exponential phases, a rapid phase [time constant (msec): tau 1] followed by a slower one (time constant: tau 2). When the total load increased, tau 1 increased and tau 2 decreased according to the linear relations: % TF = 0.2 tau 1 + 4.8 (r = 0.83) and % TF = -0.1 tau 2 + 157 (r = 0.95). The relative predominance of both the time course and the amplitude of these two phases depended upon the level of total load. The rapid process predominated at low load, the slow one at high load. The role of load and/or shortening in the time course of these two phases is discussed.

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supporting

confidence: 54%

Section: Time Course Of Sarcomere Relaxation Occurring In Two Phasesmentioning

confidence: 81%

Real-time kinetics of sarcomere relaxation by laser diffraction.

Lecarpentier¹,

Martin²,

Claes³

et al. 1985

Circulation Research

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“…A load-independent relaxation, associated with a low rate of activation decay secondary to a slow rate of calcium uptake, has been described in frog ventricle (4), in smooth muscle (25) and in mammalian myocardium after interventions leading to impaired function of the sarcoplasmic reticulum (18,23). However, a slow activation decay in atrial muscle is rather unlikely, since the tension decline during relaxation is fast.…”

Section: Introductionmentioning

confidence: 94%

Relaxation in atrial and ventricular myocardium: activation decay and different load sensitivity

et al. 1983

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Isolated atrial and ventricular preparations from rat heart have been compared. In atrial specimens relaxation is faster than in papillary muscles both in isometric and isotonic conditions. In papillary muscles the tension decay occurs earlier in isotonic than isometric contractions and a stretch applied at or after the peak of isometric twitches promotes a faster relaxation: this load dependence of relaxation is less pronounced in atrial specimens. The decay of activation, evaluated from the decline of the muscle shortening ability, is faster in atrium than in ventricle. These findings suggest that the sensitivity of relaxation to the loading conditions might be determined by both the activation decay rate and the cross bridge kinetics.

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“…This factor can be identified as a delayed decline of activation. In fact, a prolonged decay of activation is associated with a reduced sensitivity of relaxation to mechanical conditions in several experimental conditions: e.g., after addition of high concentrations of caffeine (25) or Sr 2+ for Ca 2+ substitution (26). A possible explanation is that when activation declines slowly, cross bridges broken by the movement can reform.…”

Section: Time Course and Load Sensitivity Of Relaxationmentioning

confidence: 97%

“…For example, load sensitivity of the relaxation is reduced when activation is prolonged by caffeine or by the replacement of calcium by strontium (25,26). Furthermore, relaxation is less sensitive to loading conditions in atrial than in ventricular myocardium, or in rat than in cat papillary muscle, and this can be attributed to a difference in the speed of cross bridge cycling, as suggested by the values of shortening velocity and ATPase activity (27).…”

Section: Introductionmentioning

confidence: 95%

Age-dependent changes of relaxation and its load sensitivity in rat cardiac muscle

et al. 1988

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The relaxation phase and its load dependence were studied in papillary muscles isolated from the left ventricle of rats of the following ages: 20 days, 2, 8, 18, and 24 months. The myofibrillar ATPase activity and the force-velocity relation were determined in each age group in order to characterize the kinetic properties of the contractile material. Both shortening velocity and myofibrillar ATPase activity showed a progressive reduction with maturation and aging. This observation suggested an age-dependent decrease in cross bridge formation rate. The relaxation phase was characterized by its duration and the maximum rate of tension decline in isometric conditions, and by the speed of relengthening in isotonic conditions. Relaxation became faster and of shorter duration with maturation from 20 days to 2 months and then became slower and of longer duration with further maturation and aging. The sensitivity of relaxation to changes in length or load was evaluated by measuring how much earlier tension declined in the presence of a given length change. An increase in load sensitivity of relaxation was observed during maturation from 20 days to 8 months. This increase was followed by a reduction during aging from 8 to 24 months. Such a biphasic trend of the age-related changes in load sensitivity of relaxation could result from the interplay between the progressive decrease in cross bridge formation rate and a reduction in activation decay rate. The latter was suggested by the prolongation of the relaxation phase and by the maintenance of developed tension during aging.

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Isometric relaxation in rat myocardium: Load dependence and influence of caffeine

Cited by 7 publications

References 12 publications

Real-time kinetics of sarcomere relaxation by laser diffraction.

Real-time kinetics of sarcomere relaxation by laser diffraction.

Relaxation in atrial and ventricular myocardium: activation decay and different load sensitivity

Age-dependent changes of relaxation and its load sensitivity in rat cardiac muscle

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