A. Xu et N. Narayanan, Effects of aging on sarcoplasmic reticulum Ca2+-cycling proteins and theirphosphorylation in rat myocardium, AM J P-HEAR, 44(6), 1998, pp. H2087-H2094
Citations number
48
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
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 i
nvestigated the impact of aging on the contents of major SR Ca2+-cycling pr
oteins and SR protein phosphorylation by endogenous Ca2+/calmodulin-depende
nt protein kinase (CaM kinase). The studies were performed using homogenate
s 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 analy
sis showed no significant age-related difference: in the relative amounts o
f ryanodine receptor-Ca2+-release channel (RyR-CRC), the Ca2+-storage prote
in calsequestrin, Ca2+-pumping ATPase (Ca2+-ATPase), and Ca2+-ATPase-regula
tory protein phospholamban (PLB) in SR or homogenate. On the other hand, th
e relative amount of immunoreactive CaM kinase II (delta-isoform) was simil
ar to 50% lower in the aged heart. CaM kinase-mediated phosphorylation of R
yR-CRC, Ca2+-ATPase, and PLB was reduced significantly (similar to 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 reduce
d significantly with aging. Treatment of SR vesicles with anti-PLB antibody
(PLBab) invoked relatively less stimulation of Ca2+ uptake in the aged (le
ss than or equal to 26%) compared with the adult (less than or equal to 65%
) rat. Ca2+-ATPase but not PLB underwent phosphorylation by CaM kinase in P
LBab-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 fi
ndings imply that changes in the intrinsic functional properties of SR Ca2-cycling proteins and/or their phosphorylation-dependent regulation contrib
ute to impaired SR function in the aging heart.