AJP - Heart and Circulatory Physiology, Vol 239, Issue 5 674-H680, Copyright © 1980 by American Physiological Society
Spontaneous mechanical alternans in papillary muscles from atherosclerotic rabbits
D. W. Peterson, C. A. Napolitano and D. W. Griffith Jr
Mechanical alternans developed spontaneously in 5 of 17 right ventricular
papillary muscles from atherosclerotic rabbits. The rabbits had eaten an
atherogenic diet of 5% lard, 5% peanut oil, 0.5% cholesterol, and 89.5%
rabbit pellets for 116-184 days. In one muscle mechanical alternans
developed slowly and persisted. When the condition had developed fully, in
the weaker contraction the muscle shortened only 20% as far when
contracting isotonically and developed only 38% as much tension when
contracting isometrically. Added to the superfusate, calcium (5.0 mM) or
norepinephrine (1.5 X 10(-5) M) abolished the alternans. In four muscles
mechanical alternans was only temporary. Compared with the 12 muscles that
did not develop alternans, these 4, when contracting isometrically 12
times/min but not in alternans, had longer latency and required more time
to develop tension at the maximum rate and to develop peak tension.
Contracting isotonically, they required more time to accelerate to maximum
velocity of shortening and to shorten maximally. Raising the contraction
frequency to 24/min decreased the differences in performance between the
two groups. Norepinephrine (1.5 X 10(-5) M) made the differences smaller
still. We think that both the mechanical alternans and the differences in
performance between the muscles that developed alteranans and those that
did not resulted from a defect in the cardiac cell's handling of calcium.
Diet-induced changes in the lipid composition of the sarcoplasmic reticulum
or sarcolemma or both seem probable causes.
