Molecular and Cellular Biochemistry

, Volume 141, Issue 2, pp 87–95 | Cite as

Lusitropic effects of α- and β-adrenergic stimulation in amphibian heart

  • Martin Vila Petroff
  • Cecilia Mundiña-Weilenmann
  • Leticia Vittone
  • Gladys Chiappe de Cingolani
  • Alicia Mattiazzi


The effects of β and α-adrenergic stimulation in amphibian superfused hearts and ventricular strips were studied. Superfusion with 3×10−8 M isoproterenol produced a positive inotropic effect, as detected by a 92±24% increase in the maximal rate of contraction\(( + \dot T)\) and a positive lusitropic effect characterized by a decrease in both the ratio\( + \dot T/ - \dot T (23 \pm 5\% )\) (23±5%) and the half relaxation time (t1/2) (19±4%). The mechanical behavior induced by the β-agonist was associated with an increase in the intracellular cAMP levels from control values of 173±19 to 329±28 nmol/mg wet tissue. Hearts superfused with32P in the presence of isoproterenol showed a significant increase in Tn 1 phosphorylation (from 151±13 to 240±44 pmol32P/mg MF protein) without consistent changes in phosphorylation of C-protein. In sarcoplasmic reticulum membrane vesicles, no phospholamban phosphorylation was detected either by β-adrenergic stimulation of superfused hearts or when phosphorylation conditions were optimized by direct treatment of the vesicles with cAMP-dependent protein kinase (PKA) and [y32P] ATP.

The effect of α-adrenergic stimulation on ventricular strips was studied at 30 and 22°C. At 30°C, the effects of 10−5 to 10−4M phenylephrine on myocardial contraction and relaxation were diminished to non significant levels by addition of propranolol. At 22°C, blockage with propranolol left a remanent positive inotropic effect (10% of the total effect of phenylephrine) and changed the phenylephrine-induced positive lusitropic effect into a negative lusitropic action. These propranolol-resistant effects were abolished by prazosin. Our results suggest that in amphibian heart, both the inotropic and lusitropic responses to catecholamines are mainly due to a β-adrenergic stimulation which predominates over the α-adrenergic response. Phospholamban phosphorylation seems not to be involved in mediating the positive lusitropic effect of β-adrenergic agents whereas phosphorylation of troponin 1 may play a critical role.

Key words

amphibian myocardial relaxation α and β-adrenergic stimulation Ca2+ myofibrillar sensitivity protein phosphorylation 


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Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • Martin Vila Petroff
    • 1
  • Cecilia Mundiña-Weilenmann
    • 1
  • Leticia Vittone
    • 1
  • Gladys Chiappe de Cingolani
    • 1
  • Alicia Mattiazzi
    • 1
  1. 1.Centro de Investigaciones Cardiovasculares, Facultad de Ciencias MédicasUniversidad Nacional de La PlataLa PlataArgentina

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