Low temperatures slow muscle contraction velocity by affecting biochemical kinetics.
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Peer-reviewed literature demonstrates that the maximal velocity of muscle shortening and rate processes are markedly temperature dependent, with specific temperature coefficients reflecting underlying biochemical kinetics.
Heart failure is a life-threatening condition that occurs when the heart muscle becomes weakened and cannot adequately circulate blood and nutrients around the body. Omecamtiv mecarbil (OM) is a compound that has been developed to treat systolic heart failure via targeting the cardiac myosin heavy chain to increase myocardial contractility. Biophysical and biochemical studies have found that OM increases calcium (Ca2+) sensitivity of contraction by prolonging the myosin working stroke and increasing the actin-myosin cross-bridge duty ratio. Most in vitro studies probing the effects of OM on cross-bridge kinetics and muscle force production have been conducted at subphysiological temperature, even though temperature plays a critical role in enzyme activity and cross-bridge function. Herein, we used skinned, ventricular papillary muscle strips from rats to investigate the effects of [OM] on Ca2+-activated force production, cross-bridge kinetics, and myocardial viscoelasticity at physiological temperature (37°C). We find that OM only increases myocardial contractility at submaximal Ca2+ activation levels and not maximal Ca2+ activation levels. As [OM] increased, the kinetic rate constants for cross-bridge recruitment and detachment slowed for both submaximal and maximal Ca2+-activated conditions. These findings support a mechanism by which OM increases cardiac contractility at physiological temperature via increasing cross-bridge contributions to thin-filament activation as cross-bridge kinetics slow and the duration of cross-bridge attachment increases. Thus, force only increases at submaximal Ca2+ activation due to cooperative recruitment of neighboring cross-bridges, because thin-filament activation is not already saturated. In contrast, OM does not increase myocardial force production for maximal Ca2+-activated conditions at physiological temperature because cooperative activation of thin filaments may already be saturated.
Abstract The effects of temperature on contractile function of isolated, chemically skinned red (slow oxidative) and white (fast glycolytic) fibers of skeletal muscle from thermally acclimated striped bass ( Morone saxatilis ) were determined. Acclimation to 10° or 25°C has no significant effect on maximum isometric tension (P o ) or maximum unloaded contraction velocity (V o ) of fibers of either muscle type. Sensitivity to acute changes in temperature is markedly greater for slow‐twitch fibers than for white, fast‐twitch fibers. Q 10 (15–5°C) of V o is 1.58 and 2.27 and R 10 (15–5°C; analogous to Q 10 , but for parameters that are not rate functions) of P o is 1.57 and 2.17 for fibers from white and red muscle, respectively. R 10 of maximum attainable power output is 1.29 for white and 4.50 for red fibers. Power for low speed, sustained swimming is derived exclusively from red muscle in striped bass, permitting comparisons between swimming performance and contractile capacity to be drawn. For maximum sustainable swimming speed at 15°C, calculated contraction velocity of a red muscle fiber corresponds to the maximum power output of a single fiber of red muscle at 15°C. Thermal sensitivity of red muscle power output predicts that maximum sustained swimming speed of striped bass will be severely impaired at cold temperatures. However, cold acclimation induces a proliferation of the red muscle mass that may ameliorate the thermal sensitivity of red muscle contractile function.
Maximal isometric forces during both twitch and tetanus are largely temperature independent in muscles from both endothermic and ectothermic vertebrates. Anuran muscle can develop maximal force at lower temperatures than mammalian muscle. Tetanic tension is maximal at normally experienced body temperatures in a variety of animals, but twitch tension seldom is. Thermal dependence of twitch tension varies with muscle fiber type: tension decreases with increasing temperature in fast-twitch muscles and remains constant in slow-twitch muscles. In contrast to the low temperature dependence of force generation, rates of development of tension (time to peak twitch tension and tetanic rise time) and maximal velocity of shortening and power output are markedly temperature dependent, with average temperature coefficient (Q10) values of 2.0-2.5 Q10 values for rate processes of anuran muscle are only slightly lower than those of mammalian muscle. High body temperatures permit rapid rates of muscle contraction; animals active at low body temperatures do not achieve the maximal rate performance their muscles are capable of delivering. Thermal acclimation or hibernation does not appear to result in compensatory adjustments in either force generation or rate processes. In vivo, dynamic processes dependent on contractile rates are positively temperature dependent, although with markedly lower Q10 values than those of isolated muscle. Static force application in vivo is nearly temperature indep
a/P(0) for twitch fibres was found to be independent of temperature in the range 5-20 degrees C. Q(10) for b was 2.24 (10-20 degrees C), and 2.86 (5-10 degrees C).8. V(max.) for twitch fibres was calculated to be 6.34 lengths/sec at 22.5 degrees C, the average temperature in the slow fibre experiments. The maximum shortening velocity in twitch fibres is thus 6 times higher than in slow fibres.9. When loads in the range 1.1-1.4P(0) were quickly applied to an actively contracting slow fibre, lengthening of the fibre occurred in two phases, an initial rapid phase, followed by a phase of extremely slow lengthening. In corresponding experiments on twitch fibres lengthening was rapid at first and then gradually became slower.10. Factors affecting the shape of the force-velocity curve are discussed. Calculations based on A. F. Huxley's (1957) model for muscle contraction indicated that cross-bridge turnover rate is about 15 times lower in slow than in twitch fibres. Published in The Journal of physiology (1978)
Behaviour of EMG-parameters and conduction velocity in contractions with different muscle temperatures.
In the study the effect of changing muscle temperature on EMG-parameters and muscular conduction velocity was investigated for ambient temperatures of 0, 10, 20, 30, 40 degrees C. With temperatures below 20 degrees C a striking diminution of EMG-amplitudes was observed despite nearly unchanged mechanical capability. The decrease in mean frequency of surface EMG was related directly to changes in conduction velocity during cooling of the muscle whereas in fatiguing muscle contractions the mean frequency seemed to be also affected by other mechanisms.
Published in Biomedica biochimica acta (1989)
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