Decreased expression of phospholamban is not associated with lower beta-adrenergic activation in rat atria.
The aim of the study was to find out whether low phospholamban level in atria as compared with ventricles is associated with differences in sarcoplasmic reticular Ca2+-uptake and contractile performance. Relationship between phospholamban and beta-adrenergic stimulation in rat left atria and papillary muscles were examined by means of contractile measurements, sarcoplasmic reticular oxalate-supported Ca2+-uptake, and Western blotting of phosphorylated phospholamban. Phosphoprotein determination after beta-adrenergic stimulation demonstrated that the levels of Ser16 and Thr17 phosphorylated phospholamban in atria remained at about one-third of that in ventricles. However, comparison of sarcoplasmic reticular Ca2+-uptake in control and isoproterenol perfused preparations demonstrated that the effect of beta-adrenergic stimulation on sarcoplasmic reticular Ca2+-uptake was stronger in atrial preparations. Moreover, atria responded to isoproterenol with much larger increases in developed tension, contractility and relaxation rates than papillary muscles. Thus, despite lower level of phospholamban, the beta-adrenergic activation of sarcoplasmic reticular Ca2+-uptake and contractile indices are higher in atria.
Kaasik
A
A
Department of Pharmacology, University of Tartu, Estonia.
Paju
K
K
Minajeva
A
A
Ohisalo
J
J
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D016275:Atrial Function; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction; D010210:Papillary Muscles / Q000378:metabolism; D010766:Phosphorylation; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014020:Tissue Extracts / Q000737:chemistry; D016276:Ventricular Function; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D002118:Calcium; D002135:Calcium-Binding Proteins; D007545:Isoproterenol; D011433:Propranolol; D012694:Serine; D013912:Threonine; D014020:Tissue Extracts; D000099211:Phospholamban