title: Attenuated sarcomere lengthening of the aged murine left ventricle observed using two-photon fluorescence microscopy.
abstract: The Frank-Starling mechanism, whereby increased diastolic filling leads to increased cardiac output, depends on increasing the sarcomere length (Ls) of cardiomyocytes. Ventricular stiffness increases with advancing age, yet it remains unclear how such changes in compliance impact sarcomere dynamics in the intact heart. We developed an isolated murine heart preparation to monitor Ls as a function of left ventricular pressure and tested the hypothesis that sarcomere lengthening in response to ventricular filling is impaired with advanced age. Mouse hearts isolated from young (3-6 mo) and aged (24-28 mo) C57BL/6 mice were perfused via the aorta under Ca(2+)-free conditions with the left ventricle cannulated to control filling pressure. Two-photon imaging of 4-{2-[6-(dioctylamino)-2-naphthalenyl]ethenyl}1-(3-sulfopropyl)-pyridinium fluorescence was used to monitor t-tubule striations and obtain passive Ls between pressures of 0 and 40 mmHg. Ls values (in μm, aged vs. young, respectively) were 2.02 ± 0.04 versus 2.01 ± 0.02 at 0 mmHg, 2.13 ± 0.04 versus 2.23 ± 0.02 at 5 mmHg, 2.21 ± 0.03 versus 2.27 ± 0.03 at 10 mmHg, and 2.28 ± 0.02 versus 2.36 ± 0.01 at 40 mmHg, indicative of impaired sarcomere lengthening in aged hearts. Atomic force microscopy nanoindentation revealed that intact cardiomyocytes enzymatically isolated from aged hearts had increased stiffness compared with those of young hearts (elastic modulus: aged, 41.9 ± 5.8 kPa vs. young, 18.6 ± 3.3 kPa; P = 0.006). Impaired sarcomere lengthening during left ventricular filling may contribute to cardiac dysfunction with advancing age by attenuating the Frank-Starling mechanism and reducing stroke volume.
authors.affiliation: Molecular Pathogenesis and Therapeutics Graduate Program, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Michael E
authors.initials: ME
authors.lastname: Nance
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Justin T
authors.initials: JT
authors.lastname: Whitfield
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Anne K
authors.initials: AK
authors.lastname: Gibson
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Laurin M
authors.initials: LM
authors.lastname: Hanft
authors.affiliation: Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky.
authors.forename: Kenneth S
authors.identifier: http://orcid.org/0000-0001-5615-5958
authors.initials: KS
authors.lastname: Campbell
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and.
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Meininger
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri;
authors.forename: Kerry S
authors.initials: KS
authors.lastname: McDonald
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and.
authors.forename: Steven S
authors.initials: SS
authors.lastname: Segal
authors.affiliation: Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri; domeiert@health.missouri.edu.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Domeier
mesh_terms: D000367:Age Factors; D000818:Animals; D055119:Elastic Modulus; D005456:Fluorescent Dyes; D006352:Heart Ventricles / Q000166:cytology* / Q000254:growth & development; D051379:Mice; D008810:Mice, Inbred C57BL; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D012518:Sarcomeres / Q000502:physiology / Q000648:ultrastructure*
chemical_list: D005456:Fluorescent Dyes
keywords: aging; cardiomyocyte; stiffness