CONTRACTILE FUNCTION AND MYOFIBRILLAR ATPase ACTIVITY IN EXERCISE-TRAINED DOG HEART

Myocardial contractility and the enzymatic (ATPase) activity of cardiac contractile proteins were examined after exercise training using the chronically instrumented, unanesthetized dog as an experimental model. Before training, heart rate and the maximum rate of left ventricular pressure development (max dP/dt) were measured at rest and during submaximal exercise. Animals were then subjected to an 8- to 10-wk treadmill running program. Training was verified by the establishment of a 10- to 20-beat/min reduction in heart rate during submaximal exercise. After training max dP/dt was within normal limits at rest, but significantly elevated during submaximal exercise. When max dP/dt was plotted as a function of heart rate, either with the animal standing quietly on the treadmill or during submaximal exercise, a marked elevation in max dP/dt at any given heart rate was observed following training. Myofibrillar protein yield and ATPase activity values were nearly identical in left ventricles from exercise-trained and sedentary control dogs. Although exercise training by treadmill running improved contractile function in the unanesthetized dog myocardium, this response does not appear to involve alterations in myofibrillar ATPase activity.

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Nutritional modification of rat heart postnatal development

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1984.246.3.h332 ◽

1984 ◽

Vol 246 (3) ◽

pp. H332-H338 ◽

Cited By ~ 3

Author(s):

R. T. Dowell

Keyword(s):

Atpase Activity ◽

Postnatal Development ◽

Contractile Function ◽

Left Ventricular ◽

Activity Level ◽

Myofibrillar Atpase ◽

Fast Growing ◽

Growing Rats ◽

Myofibrillar Atpase Activity ◽

Slow Growing

Postnatal development of the mammalian myocardium encompasses increases in cellularity, energy producing and energy utilizing systems, and concurrent augmentation of heart contractile performance. The present study disrupted normal developmental sequences by adjusting the number of newborn rats per litter at 4 days postbirth. Fast-growing (4 rats/litter), normal (8 rats/litter), or slow-growing (16 rats/litter) animals were studied when 21 days old. Left ventricular cellularity (total DNA) increased as a function of the nutritionally modified growth of the heart, having values of 562 +/- 27, 625 +/- 33, and 791 +/- 20 (SE) micrograms in 16, 8, and 4 rats/litter groups, respectively. Low levels of systolic pressure (55 + 5 mmHg) and rate of pressure development (dP/dt, 2,670 +/- 130 mmHg/s) were noted in the slow-growing rats. Growth-related augmentation of pressure and dP/dt occurred such that adult levels (104 +/- 4 mmHg; 5,810 +/- 290 mmHg/s) were observed in 21-day-old, fast-growing rats. An enzymatic marker for aerobic metabolism (malate dehydrogenase) indicated mitochondrial accumulation in excess of ventricular tissue, thereby establishing progressive increases in aerobic capacity. Myofibrillar ATPase activity was not significantly different among all groups. Thus heart contractile function during nutritionally induced changes in postnatal development is augmented in proportion to increases in heart DNA content. A positive relationship also exists between dP/dt and number of mitochondria; however, enhanced contractile function is achieved independently of myofibrillar ATPase activity level.

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Dissociation of myofibrillar atpase activity and contractile function in hypertrophied guinea pig hearts

Journal of Molecular and Cellular Cardiology ◽

10.1016/s0022-2828(85)80284-4 ◽

1985 ◽

Vol 17 ◽

pp. 47-47 ◽

Cited By ~ 1

Author(s):

A WALDENSTROM ◽

Y LECARPENTIER ◽

M CLERGUE ◽

P OLIVIERO ◽

K SCHWARTZ ◽

...

Keyword(s):

Guinea Pig ◽

Atpase Activity ◽

Contractile Function ◽

Myofibrillar Atpase ◽

Myofibrillar Atpase Activity

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Thermal sensitivity of contractile function in chain pickerel, Esox niger

Canadian Journal of Zoology ◽

10.1139/z85-119 ◽

1985 ◽

Vol 63 (4) ◽

pp. 811-816 ◽

Cited By ~ 8

Author(s):

Bruce D. Sidell ◽

Ian A. Johnston

Keyword(s):

Atpase Activity ◽

White Muscle ◽

Contractile Function ◽

Thermal Sensitivity ◽

Muscle Fibers ◽

Temperature Sensitive ◽

Myofibrillar Atpase ◽

Thermal Dependence ◽

Tension Development ◽

Myofibrillar Atpase Activity

Maximum catalytic activity and thermal sensitivity of Mg2+–Ca2+ activated myofibrillar ATPase from either red or white muscle tissue of chain pickerel is unaffected by 4–6 weeks acclimation to temperatures of 5 or 25 °C. Arrhenius plots of myofibrillar ATPase activity from red muscle are linear over the entire range of assay temperatures (2–32 °C; Q10 = 3.3). Similar plots of white muscle ATPase activity show a pronounced discontinuity at approximately 10 °C and a much greater thermal sensitivity below this temperature (Q10 = 11.2) than above it (Q10 = 2.2). Thermal dependence of myofibrillar ATPase activity from white muscle does not accurately predict the effect of temperature upon contraction velocities of isolated white muscle fibers. Contraction velocity of single chemically skinned white muscle fibers was sevenfold less temperature sensitive than ATPase activity below the 10 °C transition and 1.6-fold less temperature sensitive above this temperature (Q10 (0–27 °C) = 1.6). Maximum Ca2+-activated tension development was particularly temperature independent (Q10 = 1.2), ranging from 14 ± 1.6 N/cm2 at 5 °C to 20.9 ± 2.1 N/cm2 at 25 °C. Power output chain pickerel muscle, a product of these two parameters (force × velocity), should therefore show a relatively low thermal dependence (Q10 < 2) over the normal range of habitat temperatures.

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