Treadmill running increases the calcium sensitivity of myofilaments in diabetic rats

Abstract

The cardiovascular benefits of regular exercise are unequivocal, yet patients with type 2 diabetes respond poorly to exercise due to a reduced cardiac reserve. The contractile response of diabetic cardiomyocytes to beta-adrenergic stimulation is attenuated, which may result in altered myofilament calcium sensitivity and post-translational modifications of cardiac troponin I (cTnI). Treadmill running increases myofilament calcium sensitivity in non‑diabetic rats, and thus we hypothesized that endurance training would increase calcium sensitivity of diabetic cardiomyocytes and alter site-specific phosphorylation of cTnI. Calcium sensitivity, or pCa50, was measured in Zucker Diabetic Fatty (ZDF) non-diabetic (nDM) and diabetic (DM) rat hearts after 8 weeks of either a sedentary (SED) or progressive treadmill running (TR) intervention. Skinned cardiomyocytes were connected to a capacitance-gauge transducer and a torque motor to measure force as a function of pCa (‑log[Ca2+]). Specific phospho-sites on cTnI and O‑GlcNAcylation were quantified by immunoblot and total protein phosphorylation by fluorescent gel staining (ProQ Diamond). The novel finding in this study was that training increased pCa50 in both DM and nDM cardiomyocytes (p = 0.009). Phosphorylation of cTnI amino acid residues Ser23/24, a crucial protein kinase A site, and Threonine (Thr)144, was lower in DM hearts, but there was no effect of training on site-specific phosphorylation. Additionally, total phosphorylation and O-GlcNAcylation levels were not different between SED and TR groups. These findings suggest that regular exercise may benefit the diabetic heart by specifically targeting myofilament contractile function.

The carbon monoxide prodrug oCOm‐21 increases Ca2+ sensitivity of the cardiac myofilament

“…Permeabilized LV cardiomyocytes isolated from male Sprague Dawley rats were used to examine changes in Ca 2+ sensitivity as described previously (Greenman et al., 2022 ; Ng et al., 2022 ). Briefly, frozen LV tissue was homogenized in a Relax buffer (100 mM KCl, 1.75 mM EGTA, 10 mM imidazole, 4 mM ATP, 5 mM MgCl 2 , pH 7) with HALT protease and phosphatase inhibitor cocktail.…”

Electrically stimulated in vitro heart cell mimic of acute exercise reveals novel immediate cellular responses to exercise: Reduced contractility and metabolism, but maintained calcium cycling and increased myofilament calcium sensitivity

“…1 Aerobic endurance exercise training improves a number of cardiac and cardiomyocyte indices of contractile capacity and performance, evidenced by studies in both humans, 2 and experimental animals. [3][4][5][6][7][8] In these studies, regular exercise training improves cardiomyocyte contractility as measured during resting basal conditions as well as during increased heart rates and stimulation frequencies that occur during the actual exercise, and this is typically superseded by improved intracellular transmembrane and SR Ca 2+ handling, 4,5,9 increased myofilament Ca 2+ sensitization and force generation, 3,10 faster diastolic SR reuptake of Ca 2+ , 8 as well as metabolic adaptations that enhance generation of ATP 11 ; hence, the key determinants of cardiac pump capacity.…”