title: Effects of aging on phospholamban phosphorylation and calcium transport in rat cardiac sarcoplasmic reticulum.
abstract: Acceleration of cardiac relaxation upon beta adrenergic stimulation is due, in part, to enhancement in the rate of Ca2+ sequestration by the sarcoplasmic reticulum (SR) Ca2+ pump resulting from cAMP-mediated phosphorylation of the SR protein phospholamban. Our previous studies have shown that in rat myocardium, beta adrenergic activation of adenylate cyclase and the Ca2+ pump activity of SR decline with aging (Mech. Ageing Dev., 19 (1982) 127-139; 38 (1987) 127-143). In the present study, the effect of aging on phospholamban phosphorylation and consequent changes in SR Ca2+ pump activity were evaluated using cardiac SR from 6 (young adult), 12 (adult) and 28 (aged) months old rats. No age-related differences were observed in the rate or maximum level of phospholamban phosphorylation by exogenous cAMP-dependent protein kinase. The rates of ATP-dependent Ca2+ uptake by SR from young adult and aged rats were stimulated upon phospholamban phosphorylation, the percentage stimulation of Ca2+ uptake at varying Ca2+ concentrations (0.24-11.9 microM) was not diminished with aging. However, the rates of Ca2+ uptake by phosphorylated and unphosphorylated SR were remarkably lower (35-50%) in the aged. Regardless of the age of rats, the stimulatory effect of phosphorylation on Ca2+ uptake by SR was due to increase in Vmax of Ca2+ transport with no appreciable changes in K0.5 for Ca2+. These findings imply that in spite of the age-associated decline in SR Ca2+ pump activity, the ability of phospholamban to undergo cAMP-mediated phosphorylation and the relative responsiveness of the SR Ca2+ pump to phospholamban phosphorylation are not diminished in the aging heart.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: M T
authors.initials: MT
authors.lastname: Jiang
authors.forename: N
authors.initials: N
authors.lastname: Narayanan
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D000099211:Phospholamban
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium; D002135:Calcium-Binding Proteins; D011494:Protein Kinases; D000099211:Phospholamban