Integrins are considered to be an important mechanosensor in cardiac myocytes. To test whether integrins can influence cardiac contractile function, the force-frequency relationships of mouse papillary muscle bundles were measured in the presence or absence of a synthetic integrin-binding peptide, GRGDNP (gly-arg-gly-asp-asn-pro). Results demonstrate that in the presence of an arginine-glycine-aspartic acid (RGD)-containing synthetic peptide, contractile force was depressed significantly by, 28% at 4 Hz, 37.7% at 5 Hz and 20% at 10 Hz (n = 6, P < 0.01). Treatment of myofibres with either protease-generated fragments of denatured collagen (Type I) or denatured collagen that contain the RGD motif, also reduced force production significantly. An integrin-activating antibody for β 1 integrin inhibited the force similar to synthetic RGD peptide. Function-blocking integrin antibodies for α 5 and β 1 integrins reversed the effect of the RGD-containing peptide, and α 5 integrin also reversed the effect of proteolytic fragments of denatured collagen on contractile force, whereas experiments with function-blocking antibody for β 3 integrin did not reverse the effect of RGD peptide. Force-[Ca 2+ ] i measurements showed that the depressed rate of force generation observed in the presence of the RGD-containing peptide was associated with reduced [Ca 2+ ] i . Data analyses further demonstrated that force per unit of Ca 2+ was reduced, suggesting that the myofilament activation process was altered. In addition, inhibition of PKC enzyme using the selective, cell-permeable inhibitor Ro-32-0432, reversed the activity of RGD peptide on papillary muscle bundles. In conclusion, these data indicate that RGD peptide, acting via α 5 β 1 integrin, depresses the force production from papillary muscle bundles, partly associated with changes in [Ca 2+ ] i and the myofilament activation processes, that is modulated by PKCε.
Muthuchamy. Changes in end-to-end interactions of tropomyosin affect mouse cardiac muscle dynamics. Am J Physiol Heart Circ Physiol 291: H552-H563, 2006. First published February 24, 2006 doi:10.1152/ajpheart.00688.2005.-The ends of striated muscle tropomyosin (TM) are integral for thin filament cooperativity, determining the cooperative unit size and regulating the affinity of TM for actin. We hypothesized that altering the ␣-TM carboxy terminal overlap end to the -TM counterpart would affect the amino-terminal association, which would alter the end-to-end interactions of TM molecules in the thin filament regulatory strand and affect the mechanisms of cardiac muscle contraction. To test this hypothesis, we generated transgenic (TG) mouse lines that express a mutant form of ␣-TM in which the first 275 residues are from ␣-TM and the last nine amino acids are from -TM (␣-TM9aa⌬). Molecular analyses show that endogenous ␣-TM mRNA and protein are nearly completely replaced with ␣-TM9aa⌬. Working heart preparations data show that the rates of contraction and relaxation are reduced in ␣-TM9aa⌬ hearts. Left ventricular pressure and time to peak pressure are also reduced (Ϫ12% and Ϫ13%, respectively). The ratio of maximum to minimum first derivatives of change in left ventricular systolic pressure with respect to time (ratio of ϩdP/dt to ϪdP/dt, respectively) is increased, but is not changed significantly. Force-intracellular calcium concentration ([Ca 2ϩ ]i) measurements from intact papillary fibers demonstrate that ␣-TM9aa⌬ TG fibers produce less force per given [Ca 2ϩ ]i compared with nontransgenic fibers. Taken together, the data demonstrate that the rate of contraction is primarily affected in TM TG hearts. Protein docking studies show that in the mutant molecule, the overall carbon backbone is perturbed about 1.5 Å , indicating that end-to-end interactions are altered. These results demonstrate that the localized flexibility present in the coiled-coil structures of TM isoforms is different, and that plays an important role in interacting with neighboring thin filament regulatory proteins and with differentially modulating the myofilament activation processes.force-calcium; thin filament; force-frequency; myofilament activation IN REGULATED STRIATED muscle, a continuous dimerized strand of tropomyosin (TM) spans the entire length of the actin filament. Because the length of TM is much shorter than filamentous actin, contiguous TMs must interact via end-to-end interactions involving the last nine amino acids of one TM with the first nine amino acids of the next TM (27). Such interactions between contiguous TMs have been confirmed in X-ray crystallography studies (41,49,50). Historically, the end-toend interactions of adjacent TM molecules have been thought to be necessary for thin filament cooperativity (17,18,42). Strong intermolecular bonds between contiguous TMs enable a longer segment of the molecule to move from the "blocked" or "closed" state on actin to the "open" state (10) upon the binding of an ...
Objective Test the hypothesis that exercise training enhances sustained relaxation to persistent endothelium-dependent vasodilator exposure via increased nitric oxide contribution in small coronary arteries of control and ischemic hearts. Methods Yucatan swine were designated to a control group or a group in which an ameroid constrictor was placed around the proximal LCX. Subsequently, pigs from both groups were assigned to exercise (5 days/week; 16 weeks) or sedentary regimens. Coronary arteries (~100–350 μm) were isolated from control pigs and from both nonoccluded and collateral-dependent regions of chronically-occluded hearts. Results In arteries from control pigs, training significantly enhanced relaxation responses to increasing concentrations of bradykinin (10−10 to 10−7 M) and sustained relaxation to a single bradykinin concentration (30 nM), which were abolished by NOS inhibition. Training also significantly prolonged bradykinin-mediated relaxation in collateral-dependent arteries of occluded pigs, which was associated with more persistent increases in endothelial cellular Ca2+ levels, and reversed with NOS inhibition. Protein levels for eNOS and p-eNOS-(Ser1179), but not caveolin-1, Hsp90, or Akt, were significantly increased with occlusion, independent of training state. Conclusions Exercise training enhances sustained relaxation to endothelium-dependent agonist stimulation in small arteries of control and ischemic hearts by enhanced nitric oxide contribution and endothelial Ca2+ responses.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.