title: Comparison of cross-bridge cycling kinetics in neonatal vs. adult rat ventricular muscle.
abstract: The developmental shift in contractile protein isoform expression in the rodent heart likely affects actin-myosin cross-bridge interactions. We compared the Ca2+ sensitivity for force generation and cross-bridge cycling kinetics in neonatal (postnatal days 0-3) and adult (day 84) rats. The force-pCa relationship was determined in Triton-X skinned muscle bundles activated at pCa 9.0 to 4.0. In strips maximally activated at pCa 4.0, the following parameters of cross-bridge cycling were measured: (1) rate of force redevelopment following rapid shortening and restretching (ktr); and (2) isometric stiffness at maximal activation and in rigor. The fraction of attached cross-bridges (alpha fs) and apparent rate constants for cross-bridge attachment (fapp) and detachment (gapp) were derived assuming a two-state model for cross-bridge cycling. Compared to the adult, the force-pCa curve for neonatal cardiac muscle was significantly shifted to the left. Neonatal cardiac muscle also displayed significantly smaller alpha fs, slower ktr and fapp; however, gapp was not significantly different between age groups. These data indicate that weaker force production in neonatal cardiac muscle involves, at least in part, less efficient cross-bridge cycling kinetics.
authors.affiliation: Department of Anesthesiology, Mayo Clinic and Foundation, Rochester, MN 55905, USA. prakash.ys@mayo.edu
authors.forename: Y S
authors.initials: YS
authors.lastname: Prakash
authors.forename: M J
authors.initials: MJ
authors.lastname: Cody
authors.forename: P R
authors.initials: PR
authors.lastname: Housmans
authors.forename: J D
authors.initials: JD
authors.lastname: Hannon
authors.forename: G C
authors.initials: GC
authors.lastname: Sieck
mesh_terms: D000375:Aging / Q000502:physiology; D000818:Animals; D005260:Female; D009200:Myocardial Contraction / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016276:Ventricular Function