Exercise conditioning increases rat myocardial calcium uptake.
To investigate potential mechanisms underlying the enhanced myocardial performance consequent to exercise training, the adrenergic receptors of myocardial tissue and Ca2+ uptake into sarcoplasmic reticulum-enriched fractions from exercise conditioned animals were compared with that of sedentary controls. Female Wistar rats were exercised by swimming 30 min (5 days/wk) for 12 wk. Exercise conditioning was effective in producing myocardial hypertrophy, as reflected by an increase in heart weight (1.179 +/- 0.022 vs. 1.031 +/- 0.020 g, P less than 0.001) and heart weight-to-body weight ratio (3.29 +/- 0.06 vs. 2.77 +/- 0.05 X 10(-3), P less than 0.001) but no difference in body weight. Despite the myocardial hypertrophy, neither the affinity nor the density of the alpha 1-adrenergic receptors or the beta-adrenergic receptors determined by Scatchard analysis of the ligands [3H]prazosin and [3H]dihydroalprenolol were significantly different between the two groups. The basal Ca2+ uptake into the sarcoplasmic reticulum was also similar (9.90 +/- 0.97 vs. 9.04 +/- 0.75 nmol/mg protein/min), but the addition of calmodulin produced a significantly greater increment in Ca2+ uptake into sarcoplasmic reticulum from the exercised-conditioned animals (1.90 +/- 0.23 vs. 1.21 +/- 0.19 nmol/mg protein/min, P less than 0.03). The adenosine triphosphatase (ATPase) activities of the sarcoplasmic reticulum-enriched fractions of the two groups were similar. We conclude that exercise conditioning produces an enhancement of calmodulin-mediated calcium uptake that is independent of any effect on Ca2+-ATPase.
Levine
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Kinasewitz
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D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D006332:Cardiomegaly / Q000378:metabolism; D005260:Female; D007473:Ion Channels / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002147:Calmodulin; D007473:Ion Channels; D011941:Receptors, Adrenergic; D000252:Calcium-Transporting ATPases; D002118:Calcium