Comparison of contractile performance of canine atrial and ventricular muscles.

Abstract

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...

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

“…A number of biochemical (6,29) and mechanical (16,27,28) differences between atrial and ventricular myocardium have been recently described. In particular, evidence that these tissues exhibit differential relaxation properties has been provided by Couttenye et al (5).…”

Relaxation properties of mammalian atrial muscle.

“…This induces a Venturi effect on the valve leaflets and sucks them closely together. This enhanced velocity of shortening of the atrial muscle as compared to the ventricular muscle (Urthaler et al, 1975) has been correlated with a difference in ATPase activity of atrial vs. ventricular myosin (Long et al, 1977;Yazaki et al, 1979). On the other hand, the isotonic phase of the contraction and thus the shortening phase, albeit faster, should be maintained as long as possible to allow the atrium to squeeze its content into the ventricle at end diastole, thus causing the ventricular muscle to be additionally lengthened, and thus put at a higher level of performance.…”

“…ALTHOUGH the contractile properties of the contraction phase of mammalian atrial muscle have been well studied and compared with the contractile performance of ventricular muscle (Fabiato and Fabiato, 1972;Tarr et al, 1979;Urthaler et al, 1975), its properties during the relaxation phase are less well understood. Because of the unquestionable contribution of atrial contraction to the pump function of the ventricle, and because of the significant differences between the contractile properties of atrial and ventricular muscles (Blinks and KochWeser, 1963;Koch-Weser and Blinks, 1963), we have analyzed, in the present study, the mechanical behavior of mammalian atrial muscle during relaxation and in particular, its sensitivity to load or load alterations and its possible role in the functioning of the heart.…”

Ultrastructure of cultured atrial cardiac muscle cells from adult rats

“…At least some atrial myocytes have the ability to recover from this enzyme-induced damage, since all myocytes which eventually spread out in culture passed through this rounded stage. The fact that atrial myocytes spread out after shorter culture times than cultured ventricular myocytes may be a reflection of their smaller size, decreased myofibrillar content (McNutt and Fawcett, 1969;Herbener et al, 1973;Frank et al, 1975;Sommer and Johnson, 19791, and/or looser sarcomeric arrangement (Urthaler et al, 1975). The ultrastructure of cultured atrial myocytes is at …”