title: Age-related functional effects linked to phosphatase activity in ventricular myocytes.
abstract: Conflicting reports exist regarding the influence of beta-adrenergic stimulation on the maximum velocity of shortening (Vmax) in ventricular myocytes. This may be due to an unrecognized effect of maturation. In the present study, the effects of beta-adrenergic receptor stimulation on myocytes from hearts of juvenile nonbred and young adult retired breeder female rats were compared. Ventricular myocytes from young adults had a beta-adrenergic-dependent increase in Vmax and Ca2+-dependent actomyosin ATPase that was not observed in myocytes from juveniles. Myocytes from young adults had both an increase in beta-myosin heavy chain (MHC) and higher basal serine/threonine phosphatase activity compared with juvenile rats. Additional studies established moderate increases in beta-MHC induced by hypothyroidism do not confer myocardial beta-adrenergic responsiveness, whereas inhibition of the higher phosphatase activity in myocytes from young adults blocks the age-dependent, beta-adrenergic-induced increase in cross-bridge cycling rates. We propose that the higher phosphatase activity of myocytes from young adults compared with juveniles allows for a greater functional response of the myocardium to beta-adrenergic stimulation.
authors.affiliation: Department of Physiology, University of Tennessee, Memphis, TN 38163, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Grey
authors.forename: Chun K
authors.initials: CK
authors.lastname: Chan
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Polly A
authors.initials: PA
authors.lastname: Hofmann
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000375:Aging / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D003994:Bucladesine / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004791:Enzyme Inhibitors; D005260:Female; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology; D007037:Hypothyroidism / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D032342:Muscle Cells / Q000201:enzymology*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000201:enzymology; D009210:Myofibrils / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D051381:Rats
chemical_list: D004791:Enzyme Inhibitors; D010710:Phosphates; D010761:Phosphorus Radioisotopes; D019319:Okadaic Acid; D003994:Bucladesine; D010744:Phosphoric Monoester Hydrolases; D018995:Myosin Heavy Chains; D000252:Calcium-Transporting ATPases