Ca²⁺ sensitization of cardiac myofilament proteins contributes to exercise training-enhanced myocardial function in a porcine model of chronic occlusion

Abstract

Exercise training has been shown to improve cardiac dysfunction in both patients and animal models of coronary artery disease; however, the underlying cellular and molecular mechanisms have not been completely understood. We hypothesized that exercise training would improve force generation in the myocardium distal to chronic coronary artery occlusion via altered intracellular Ca(2+) concentration ([Ca(2+)](i)) cycling and/or Ca(2+) sensitization of myofilaments. Ameroid occluders were surgically placed around the proximal left circumflex coronary artery of adult female Yucatan pigs. Twenty-two weeks postoperatively, the myocardium was isolated from nonoccluded (left anterior descending artery dependent) and collateral-dependent (formerly left circumflex coronary artery dependent) regions of sedentary (pen confined) and exercise-trained (treadmill run, 5 days/wk for 14 wk) pigs. Force measurements in myocardial strips showed that the percent change in force at stimulation frequencies of 3 and 4 Hz relative to 1 Hz was significantly higher in exercise-trained pigs compared with sedentary pigs. β-Adrenergic stimulation with dobutamine significantly improved force kinetics in myocardial strips of sedentary but not exercise-trained pigs at 1 Hz. Additionally, time to peak and half-decay of intracellular Ca(2+) (340-to-380-nm fluoresence ratio) responses at 1 Hz were significantly decreased in the collateral-dependent region of exercise-trained pigs with no difference in peak [Ca(2+)](i) between groups. Furthermore, the skinned myocardium from exercise-trained pigs showed an increase in Ca(2+) sensitivity compared with sedentary pigs. Immunoblot analysis revealed that the relative levels of cardiac troponin T and β(1)-adrenergic receptors were decreased in hearts from exercise-trained pigs independent of occlusion. Also, the ratio of phosphorylated to total myosin light chain-2, basal phosphorylation levels of cardiac troponin I (Ser(23) and Ser(24)), and cardiac myosin binding protein-C (Ser(282)) were unaltered by occlusion or exercise training. Thus, our data demonstrate that exercise training-enhanced force generation in the nonoccluded and collateral-dependent myocardium was associated with improved Ca(2+) transients, increased Ca(2+) sensitization of myofilament proteins, and decreased expression levels of β(1)-adrenergic receptors and cardiac troponin T.

Reduced RhoA Activity Mediates Acute Alcohol Intoxication‐Induced Inhibition of Lymphatic Myogenic Constriction Despite Increased Cytosolic [Ca2+]

“…We also determined the time to peak and time to half decay and found these were not altered by alcohol. It should be noted that the time to peak was much higher, and the half time for decay slightly higher than typical times observed in single cells [30, 31]. This is most likely because we determined the 340/380 ratio in a relatively large area, so that the speed at which the calcium transient was transmitted along the length of the vessel strongly influenced these parameters.…”

Ischemic preconditioning: The role of mitochondria and aging

“…We found that pharmacologic inhibition or partial genetic ablation of SIRT1 blocked IPC in adult mouse hearts (Nadtochiy et al, 2011; Nadtochiy et al, 2010), suggesting an endogenous role for SIRT1 in protection. Thus, it is possible that age-dependent decline in SIRT1 activity (Braidy et al, 2011) may contribute to loss of IPC.…”

“…For example, the mitochondrial K ATP channel (Wojtovich et al, 2009; Facundo et al, 2006) and sirtuin activity (SIRT1) (Nadtochiy et al, 2011; Nadtochiy et al, 2010) are critical components of IPC, and both exhibit an age-dependent decline in activity (Braidy et al, 2011; Krylova et al, 2006). …”

“…Thus, it is possible that age-dependent decline in SIRT1 activity (Braidy et al, 2011) may contribute to loss of IPC. Furthermore, over-expression of SIRT1 elicits resistance to oxidative stress and protects heart from IR injury (Nadtochiy et al, 2011; Hsu et al, 2008). This suggests that boosting SIRT1 activity in aging may be able to restore IPC.…”

“…The molecular mechanisms of SIRT1-mediated cardioprotection have not been fully elucidated, but SIRT1 is known to regulate a variety of potential protective events, such as eNOS activation and autophagy (Nadtochiy et al, 2011). In addition, SIRT1 is at the crossroad of the CR-mediated regulation of mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) pathways (Ghosh et al, 2010; Shinmura et al, 2007), all of which are cardioprotective.…”