Exercise training increases the Ca²⁺sensitivity of tension in rat cardiac myocytes

Abstract

The heart is known to respond to a program of chronic exercise in ways that enhance cardiac function. However, the cellular mechanisms involved in training-induced improvements in the contractile function of the myocardium are not known. In this study we tested the hypothesis that increased contractility of the myocardium associated with exercise training is due, in part, to increases in the Ca(2+) sensitivity of steady-state tension. Female Sprague-Dawley rats were randomly divided into sedentary control (C) and exercise-trained (T) groups. The T rats underwent 11 wk of progressive treadmill exercise (1 h/day, 5 days/wk, 26 m/min, 20% grade). Evidence of training effect included a 5.9% increase in heart mass, increases in heart weight-to-body weight ratio, and a 60% increase in skeletal muscle citrate synthase activity in T rats compared with C rats. After the training program, cardiac myocytes were isolated from T and C hearts. Myocytes were chemically skinned (i.e., the sarcolemma was removed) and attached to a force transducer, and steady-state tension was determined in solutions of various Ca(2+) concentrations ([Ca(2+)]). Myocytes isolated from the hearts of T rats showed a significantly (P < 0.01) increased sensitivity of tension to [Ca(2+)]. The [Ca(2+)] giving 50% of maximal tension (pCa(50)) was 5.90 +/- 0.033 and 5.82 +/- 0.023 (SD) in T and C myocytes, respectively (n = 70 myocytes/group). This result suggests that exercise training affects the myofibrillar proteins, such that Ca(2+) sensitivity is increased, and that this may be the mechanism that underlies, at least in part, the effect of training to increase myocardial contractility.

Hemodynamic effects of atrial natriuretic peptide in ischemia-reperfusioninjury that occurs after exercise

“…Looking at the cardiac muscles, it has been indicated that 3 or 5 consecutive days of treadmill exercise improves myocardial contractility via increased myocardial left ventricular heat shock protein 72, glutathione, and manganese superoxide dismutase activities during ischemia and reperfusion (19). Increasing Ca +2 sensitivity has also been shown as a part of the mechanism involved in training-induced improvements in the contractility function of the myocardium (20). Coronary vascular resistance has been accepted as the other remarkable factor that regulates cardiac responses to exercise (21).…”

Aerobic interval training enhances cardiomyocyte contractility and Ca2+ cycling by phosphorylation of CaMKII and Thr-17 of phospholamban

“…Improved myofilament sensitivity to Ca 2+ is an important adaptation of the rat heart to regular exercise training [1][2][3]21], and is now also indicated in the mouse heart. The CaMKblockade maneuver in trained cardiomyocytes caused Ca 2+ sensitivity to revert toward levels closer to sedentary controls; hence, suggesting that CaMK partly modulates the traininginduced improvement in Ca 2+ sensitivity.…”

Gnawing bones as enrichment for farmed blue foxes (Vulpes lagopus)

“…), percentage of animals with dental calculus in December and severity of dental calculus on a subjective scale where 0 denotes 'no dental calculus' and 3 'severe dental calculus' (mean 6 s.e.) in the juvenile blue foxes in the bone and control group be used as an indicator of exercise (Duncan et al, 1998;Diffee et al, 2001), whereas the mass of brain has been observed to increase in enriched living conditions for example in mice and rats (Henderson, 1970;Ferchmin et al, 1975;Rosenzweig and Bennett, 1996;Iso et al, 2007). Of these variables, only the masses of liver and adrenals suggested that gnawing bones might have some effects on the welfare of these animals: both the mass of liver and mass of adrenals tended to be higher in bone than in control group foxes.…”