Effects of Various Inotropic Interventions on the Dynamic Properties of the Contractile Elements in Heart Muscle of the Cat

Brutsaert, Dirk L.; Parmley, William W.; Sonnenblick, Edmund H.

doi:10.1161/01.res.27.4.513

Cited by 22 publications

(16 citation statements)

References 19 publications

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“…There are also significant differences between the pharmacological responses of atrial and ventricular muscles (15,16). Whereas abundant information is available about the mechanical behavior of ventricular myocardium (15)(16)(17)(18)(19)(20)(21)(22)(23), much less is known about atrial myocardial performance, and conflicting results have been reported (15,16,24). Differences in the reported results may be due in part to considerable species variability (15,16) and in part to the fact that published accounts have often failed to emphasize how the results were obtained under significantly different experimental conditions (15,16).…”

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Comparison of contractile performance of canine atrial and ventricular muscles.

Urthaler¹,

Walker²,

Hefner³

et al. 1975

Circulation Research

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This study compared the contractile performance of a canine right atrial trabecula with that of a macroscopically indistinguishable trabecula isolated from the right ventricular apex. The heart was removed from nine mongrel puppies weighing 6-8 kg and placed in Krebs-Ringer's bicarbonate solution. The bathing solution contained only 1.25 mmoles of Ca 2+ and was bubbled with a 95% O 2 -5% CO 2 gas mixture. Each atrial trabecula was specially selected from the right atrial appendage. Histologically, these trabeculae showed a remarkable longitudinal orientation of the fibers. At L max (the length of the muscle at which developed tension was maximum) under identical conditions of temperature, rate of stimulation, ionic milieu, pH, and O 2 and CO 2 supply, right atrial trabeculae achieved the same developed and total tensions but in a much shorter time than did ventricular trabeculae. In both muscle groups the maximum developed tension averaged about 2.5 g/mm 2 . Since L o (expressed as a fraction of L max ) was less in atrial muscle than it was in ventricular muscle, we concluded that atrial muscle can be stretched considerably more than can ventricular muscle before optimum length is reached. At any given initial muscle length, the maximum of tension rise for atrial trabeculae amounted to at least twice that for ventricular trabeculae. At any given load up to 1.5 g/mm 2 , the maximum velocity of shortening of an atrial trabecula was about three to four times that of a ventricular trabecula. These results collectively indicate that the contractile performance of the right atrial muscle is in many respects superior to that of the right ventricle, at least under the conditions of these experiments.• The working myocardial cells of the cardiac atria differ morphologically from those of the ventricles (1-14). Atrial myocytes are smaller, branch less often, have fewer if any transverse tubules, and contain specific granules that are not found in ventricular myocytes. There are also significant differences between the pharmacological responses of atrial and ventricular muscles (15,16). Whereas abundant information is available about the mechanical behavior of ventricular myocardium (15-23), much less is known about atrial myocardial performance, and conflicting results have been reported (15,16,24). Differences in the reported results may be due in part to considerable species variability (15, 16) and in part to the fact that published accounts have often failed to emphasize how the results were obtained under significantly different experimental conditions (15, 16). Although dogs are among the most frequently used animals in the experimental cardiovascular laboratory, we can find no report comparing the mechanical properties of canine right atrial and right ventricular trabeculae. This work was supported by U. S. Public Health Service Grant HL 11,310 from the National Heart and Lung Institute and by MIRU Contract 4367-1441.Received March 10, 1975. Accepted for publication September 12, 1975. The present study...

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Comparison of contractile performance of canine atrial and ventricular muscles.

Urthaler¹,

Walker²,

Hefner³

et al. 1975

Circulation Research

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“…The influence of Ca on the mechanical performance of isolated skinned and glycerinated fibers of skeletal muscle has been studied recently (1,(3)(4)(5)(6)(7)(8)(9). Potentiating effects of Ca on the contractile properties of isolated intact cardiac muscle have been observed (10,11); some investigators suggest that Ca augments force development (P o ) and maximum shortening velocity (Vmax) extrapolated from force-peak velocity relations of afterloaded contractions (10,12), but such derivations of Vmax are subject to methodological criticism (13,14). More recently Ca has been shown to influence force development in glycerinated cardiac muscle fibers (15), but the important question of how Ca influences the whole forcevelocity relation in heart muscle remains a controversial issue.…”

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“…More recently Ca has been shown to influence force development in glycerinated cardiac muscle fibers (15), but the important question of how Ca influences the whole forcevelocity relation in heart muscle remains a controversial issue. From a biochemical standpoint, Katz (16) has challenged the view that in cardiac muscle Ca really affects Vmax or the maximum rate of turnover at a single myosin crossbridge, maintaining that the influence of Ca is wholly explicable in terms of the number of crossbridges it activates and that previous observations of changes in Vmax (10,12) are unreliable or attributable to an internal load.…”

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Effect of Calcium on Force-Velocity-Length Relations of Heart Muscle of the Cat

Brutsaert

Claes

Goethals

1973

Circulation Research

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The influence of calcium concentration in the bathing solution on the force-velocity relations of the isolated, electrically excited cat papillary muscle was examined. Shortening velocity was directly measured at minimum loads by unloading or load clamping the muscle from the preload (at the length, Lmax, where maximum active tension was developed) to 0 (zero-load clamp), 2, 5, 10, and 15% of the total tension, P o . All measurements were made in the physiological length range between Lmax and 12.5% below Lmax. Increasing the calcium concentration augmented the measured maximum unloaded shortening velocity and shifted the normalized force-velocity relation when force was expressed as a fraction of P o . These observations suggest that the activating calcium has an action more complex than the binding to troponin alone.

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“…It represents the total myocardial wall force at zero CE shortening velocity and has been considered as a suitable measure of muscle activation [15] both with regard to its time course as to its dependency on contractile state [2,9,12]. Po was found as a result of the curve fitting procedure which in this respect acted as an extrapolation technique.…”

Section: Resultsmentioning

confidence: 99%

“…Note that for VcE = 0: F = Fo. During isometric contraction shortening velocity of the CE is related to the rate of force development by: Combining (1), (2) and (3) rate of force development before and after the QVR is found from:…”

Section: Methodsmentioning

confidence: 99%

Left ventricular force-velocity relations measured from quick volume changes

Schiereck

Boom

1979

Pflugers Arch.

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Abstract. Left ventricles of rabbit hearts were subjected to series of quick volume releases (QVR) -taking place within 6 ms -applied at fixed times in the cardiac cycle. The hearts were paced artificially and allowed to contract isovolumically. The QVR was used as a tool for realizing predetermined pressure values at any time during the ascending limb of the intra-ventricular pressure curve. Any desired pressure could be attained by suitable choice of the QVR amplitude. By relating dP/dt values occuring immediately after the QVR to the pressure attained by the QVR for different QVR amplitudes, instantaneous dP/dt relations were obtained. Time effects on these relations were studied by repeating the QVR series with increasing amplitudes at different but constant times. Influences of volume and contractile state were examined by varying end diastolic pressure (EDP) and the perfusate [Ca 2 + ]. The data were fitted with a dP/dt-P relation derived from the Hill equation using a simple geometric model of the ventricle and a two element model of the myocardium. The experimental relations were described adequately by the model. The parameters in the Hill equation estimated for heart muscle were compared to those previously reported on heart muscle experiments. Parameter values obtained were: a/Fo: 0.001 -1.3; Fo (mean maximal force for VcE = 0): 12.5-3.5N; b: 1.7-13.2 cm/s. F o rises at the beginning of systole and shows a plateau from ca. 60-100% time of peak pressure. This time course was influenced by changes in EDP and [Ca 2 +]. Parameter b exhibits a time course comparable to that of ventricular pressure. It was not influenced by EDP changes and only slightly increased by an increase in [Ca2+].

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Effects of Various Inotropic Interventions on the Dynamic Properties of the Contractile Elements in Heart Muscle of the Cat

Cited by 22 publications

References 19 publications

Comparison of contractile performance of canine atrial and ventricular muscles.

Comparison of contractile performance of canine atrial and ventricular muscles.

Effect of Calcium on Force-Velocity-Length Relations of Heart Muscle of the Cat

Left ventricular force-velocity relations measured from quick volume changes

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