Energetics of the Frank-Starling effect in rabbit myocardium: economy and efficiency depend on muscle length.
We tested the hypothesis that economy and efficiency are independent of length in intact cardiac muscle over its normal working range. We measured force, force-time integral, force-length area, and myocardial oxygen consumption in eight isometrically contracting rabbit right ventricular papillary muscles. 2,3-Butanedione monoxime was used to partition nonbasal oxygen consumption into tension-independent and tension-dependent components. Developed force, force-time integral, and force-length area increased by factors of 2.4, 2.7, and 4.8, respectively, as muscle length was increased from 90% to 100% maximal length, whereas tension-dependent oxygen consumption increased only 1.6-fold. Economy (the ratio of force-time integral to tension-dependent oxygen consumption) increased significantly with muscle length, as did contractile efficiency, the ratio of force-length area to tension-dependent oxygen consumption. The average force-length area-nonbasal oxygen consumption intercept was more than the twice tension-independent oxygen consumption. We conclude that economy and efficiency increase with length in rabbit myocardium. This conclusion is consistent with published data in isolated rabbit and dog hearts but at odds with studies in skinned myocardium.
Holmes
Jeffrey W
JW
Department of Biomedical Engineering, Columbia University, New York, New York 10027, USA. jh553@columbia.edu
Hünlich
Mark
M
Hasenfuss
Gerd
G
D000704:Analysis of Variance; D000818:Animals; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology; D011817:Rabbits; D013314:Stress, Mechanical
C004717:diacetylmonoxime; D003931:Diacetyl