Effects of sustained low-flow ischemia on myocardial function and calcium-regulating proteins in adult and senescent rat hearts.
OBJECTIVE
Both aging and myocardial ischemia are associated with alterations of calcium-regulating proteins. We investigated the effects of graded levels of low-flow ischemia on myocardial function and on SR Ca(2+)-ATPase (SERCA2), Na(+)-Ca2+ exchanger (NCX) and ryanodine receptor (RyR2), at mRNA and protein levels in both adult and senescent myocardium.


METHODS
Isolated hearts from 4 and 24 month old (mo) rats were retrogradely perfused during 180 min at 100% (100% CF, n = 11 and n = 11 respectively. 30% (30% CF, n = 10 and n = 12) or 15% (15% CF, n = 13 and n = 8) of their initial coronary flow, and active tension and coronary resistance (in % of their baseline value) were recorded. After 180 min of perfusion. NCX, RyR2 and SERCA2 mRNAs (in % of age-matched 100% CF group value) and protein levels were quantitated in the left ventricles by slot blot and Western blot analysis, respectively.


RESULTS
In 24 mo hearts, low-flow ischemia induced a greater fall in active tension (-65 +/- 7% vs. -40 +/- 4% in 4 mo 30% CF, p, 0.01 and -82 +/- 2% vs. -60 +/- 5% in 4 mo 15% CF groups, p < 0.05 after 15 min of ischemia) and a greater increase in coronary resistance (+357 +/- 44% vs. +196 +/- 39% in 4 mo 30% CF, p < 0.05 and +807 +/- 158% vs. +292 +/- 61% in 4 mo 15% CF groups, p < 0.001 after 15 min of ischemia). An increased accumulation of SERCA2 (+36% and NCX (+46%) transcripts, but not RyR2, already occurred in 24 mo 30% CF group while the 3 transcripts accumulated in 24 mo 15% CF group. In 4 mo rats SERCA2 (+26%), NCX (+35%) and RyR2 (+81%) mRNA levels only increased in the 15% CF group. Corresponding calcium-regulating protein levels were unaltered whatever the degree of flow reduction in both 4 mo and 24 mo hearts.


CONCLUSIONS
Low-flow ischemia does not induce calcium-regulating protein loss in both adult and senescent hearts. The increase in mRNAs coding for calcium-handling proteins and the impairment of myocardial function which occur at a lesser degree of coronary flow reduction in senescent hearts, indicate a higher vulnerability to low-flow ischemia during aging.
Assayag
P
P
Groupe de Physiophathologie Cellulaire Cardiaque, ESA CNRS 5077, Université Joseph Fourier, Grenoble, France.
CHarlemagne
D
D
Marty
I
I
de Leiris
J
J
Lompré
A M
AM
Boucher
F
F
Valére
P E
PE
Lortet
S
S
Swynghedauw
B
B
Besse
S
S
D000375:Aging; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D008297:Male; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000378:metabolism / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; D000252:Calcium-Transporting ATPases