Effects of aging on sarcoplasmic reticulum Ca2+-cycling proteins and their phosphorylation in rat myocardium.
Diminished Ca2+-sequestering activity of the sarcoplasmic reticulum (SR) is implicated in the age-associated slowing of cardiac muscle relaxation. In attempting to further define the underlying mechanisms, the present study investigated the impact of aging on the contents of major SR Ca2+-cycling proteins and SR protein phosphorylation by endogenous Ca2+/calmodulin-dependent protein kinase (CaM kinase). The studies were performed using homogenates and SR vesicles derived from the ventricular myocardium of adult (6-8 mo old) and aged (26-28 mo old) Fischer 344 rats. Western immunoblotting analysis showed no significant age-related difference in the relative amounts of ryanodine receptor-Ca2+-release channel (RyR-CRC), the Ca2+-storage protein calsequestrin, Ca2+-pumping ATPase (Ca2+-ATPase), and Ca2+-ATPase-regulatory protein phospholamban (PLB) in SR or homogenate. On the other hand, the relative amount of immunoreactive CaM kinase II (delta-isoform) was approximately 50% lower in the aged heart. CaM kinase-mediated phosphorylation of RyR-CRC, Ca2+-ATPase, and PLB was reduced significantly ( approximately 25-40%) in the aged compared with adult rat. ATP-dependent Ca2+-uptake activity of SR and the stimulatory effect of calmodulin on Ca2+ uptake were also reduced significantly with aging. Treatment of SR vesicles with anti-PLB antibody (PLBab) invoked relatively less stimulation of Ca2+ uptake in the aged (</=26%) compared with the adult (</=65%) rat. Ca2+-ATPase but not PLB underwent phosphorylation by CaM kinase in PLBab-treated SR with resultant stimulation of Ca2+ uptake. The rates of Ca2+ uptake by PLBab-treated SR were significantly lower (45-55%) in the aged compared with adult rat in the absence and presence of calmodulin. These findings imply that changes in the intrinsic functional properties of SR Ca2+-cycling proteins and/or their phosphorylation-dependent regulation contribute to impaired SR function in the aging heart.
Xu
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Department of Physiology, The University of Western Ontario, London, Ontario, Canada N6A 5C1.
Narayanan
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D000375:Aging / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011916:Rats, Inbred F344; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000252:Calcium-Transporting ATPases; D002155:Calsequestrin; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban