Effect of exercise training on Ca2+ release units of left ventricular myocytes of spontaneously hypertensive rats

In cardiomyocytes, calcium (Ca2+) release units comprise clusters of intracellular Ca2+ release channels located on the sarcoplasmic reticulum, and hypertension is well established as a cause of defects in calcium release unit function. Our objective was to determine whether endurance exercise training could attenuate the deleterious effects of hypertension on calcium release unit components and Ca2+ sparks in left ventricular myocytes of spontaneously hypertensive rats. Male Wistar and spontaneously hypertensive rats (4 months of age) were divided into 4 groups: normotensive (NC) and hypertensive control (HC), and normotensive (NT) and hypertensive trained (HT) animals (7 rats per group). NC and HC rats were submitted to a low-intensity treadmill running protocol (5 days/week, 1 h/day, 0% grade, and 50-60% of maximal running speed) for 8 weeks. Gene expression of the ryanodine receptor type 2 (RyR2) and FK506 binding protein (FKBP12.6) increased (270%) and decreased (88%), respectively, in HC compared to NC rats. Endurance exercise training reversed these changes by reducing RyR2 (230%) and normalizing FKBP12.6 gene expression (112%). Hypertension also increased the frequency of Ca2+ sparks (HC=7.61±0.26 vs NC=4.79±0.19 per 100 µm/s) and decreased its amplitude (HC=0.260±0.08 vs NC=0.324±0.10 ΔF/F0), full width at half-maximum amplitude (HC=1.05±0.08 vs NC=1.26±0.01 µm), total duration (HC=11.51±0.12 vs NC=14.97±0.24 ms), time to peak (HC=4.84±0.06 vs NC=6.31±0.14 ms), and time constant of decay (HC=8.68±0.12 vs NC=10.21±0.22 ms). These changes were partially reversed in HT rats (frequency of Ca2+ sparks=6.26±0.19 µm/s, amplitude=0.282±0.10 ΔF/F0, full width at half-maximum amplitude=1.14±0.01 µm, total duration=13.34±0.17 ms, time to peak=5.43±0.08 ms, and time constant of decay=9.43±0.15 ms). Endurance exercise training attenuated the deleterious effects of hypertension on calcium release units of left ventricular myocytes.

Effect of exercise training on Ca²âº release units of left ventricular myocytes of spontaneously hypertensive rats.

In cardiomyocytes, calcium (Ca²âº) release units comprise clusters of intracellular Ca²âº release channels located on the sarcoplasmic reticulum, and hypertension is well established as a cause of defects in calcium release unit function. Our objective was to determine whether endurance exercise training could attenuate the deleterious effects of hypertension on calcium release unit components and Ca²âº sparks in left ventricular myocytes of spontaneously hypertensive rats. Male Wistar and spontaneously hypertensive rats (4 months of age) were divided into 4 groups: normotensive (NC) and hypertensive control (HC), and normotensive (NT) and hypertensive trained (HT) animals (7 rats per group). NC and HC rats were submitted to a low-intensity treadmill running protocol (5 days/week, 1 h/day, 0% grade, and 50-60% of maximal running speed) for 8 weeks. Gene expression of the ryanodine receptor type 2 (RyR2) and FK506 binding protein (FKBP12.6) increased (270%) and decreased (88%), respectively, in HC compared to NC rats. Endurance exercise training reversed these changes by reducing RyR2 (230%) and normalizing FKBP12.6 gene expression (112%). Hypertension also increased the frequency of Ca²âº sparks (HC=7.61 ± 0.26 vs NC=4.79 ± 0.19 per 100 µm/s) and decreased its amplitude (HC=0.260 ± 0.08 vs NC=0.324 ± 0.10 ΔF/F0), full width at half-maximum amplitude (HC=1.05 ± 0.08 vs NC=1.26 ± 0.01 µm), total duration (HC=11.51 ± 0.12 vs NC=14.97 ± 0.24 ms), time to peak (HC=4.84 ± 0.06 vs NC=6.31 ± 0.14 ms), and time constant of decay (HC=8.68 ± 0.12 vs NC=10.21 ± 0.22 ms). These changes were partially reversed in HT rats (frequency of Ca²âº sparks=6.26 ± 0.19 µm/s, amplitude=0.282 ± 0.10 ΔF/F0, full width at half-maximum amplitude=1.14 ± 0.01 µm, total duration=13.34 ± 0.17 ms, time to peak=5.43 ± 0.08 ms, and time constant of decay=9.43 ± 0.15 ms). Endurance exercise training attenuated the deleterious effects of hypertension on calcium release units of left ventricular myocytes.

Protein restriction does not impair adaptations induced in cardiomyocytes by exercise in rats.

The effect of a treadmill running program on physical performance and morphofunctional adaptations was investigated in control and malnourished rats. Male 4-week old Wistar rats were randomized in groups of 12 animals: control trained (CT), control sedentary (CS), malnourished trained (MT) and malnourished sedentary (MS). Control and malnourished animals received chow with 12% protein or 6% protein, respectively. Trained groups were subjected to a treadmill running program for 8 weeks. Physical performance, biochemical parameters, cardiomyocytes morphology and biomechanics were determined. Malnourished animals presented reduction in body mass, serum levels of total protein, albumin and hemoglobin compared to the control groups. At 1 and 3 Hz cardiomyocytes from CT and MT showed higher cell shortening, speed of contraction and relaxation compared to the other groups. At 3 Hz cardiomyocytes from MS showed reduction in cell shortening and speed of contraction compared to CS. Protein restriction does not prevent the improvement in physical performance or cardiomyocytes biomechanical efficiency and growth in response to exercise. These findings could represent a modulatory effect of exercise to maintain cardiomyocyte growth at the expense of reducing the rate of body growth in order to ensure proper cellular function in conditions of cardiovascular overload imposed by exercise.