Decrease in tetanic tension elicited by beta-adrenergic stimulation.
The effect of beta-adrenergic stimulation on tetanic tension (TT), maximal rate of rise of tension (+TT) and phospholamban (PHL) phosphorylation were studied in the perfused rat heart. 3 x 10(-8) M isoproterenol perfused at different [Ca2+]o 0.25, 1.35 and 3.85 mM, significantly decreased TT while increased +TT and PHL phosphorylation at the three [Ca2+]o studied. Regression lines of the relationship between +TT and TT from individual data obtained at each [Ca2+]o in the presence and in the absence of isoproterenol, show that for the same level of +TT, TT is lower in the presence of isoproterenol, i.e. at high levels of PHL phosphorylation. The slopes of the lines were 0.137 s and 0.427 s (P less than 0.05) in the presence and absence of isoproterenol respectively. The decrease in TT produced by the beta-agonist can be attributed to its relaxant action prevailing over its inotropic effect and may represent the mechanical expression of the enhanced phosphorylation of phospholamban.
Napolitano
R
R
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina.
Vittone
L
L
Mundiña
C
C
Chiappe de Cingolani
G
G
Mattiazzi
A
A
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004558:Electric Stimulation; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D007545:Isoproterenol; D011943:Receptors, Adrenergic, beta; D012433:Ryanodine; D000099211:Phospholamban