Positive inotropy induced by ouabain, by increased frequency, by X537A (RO2-2985), by calcium and by isoproterenol: The lack of correlation with phosphorylation of TnI

E. G. Ezrailson, J. D. Potter, L. Michael, A. Schwartz

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Isoproterenol (5×10-6 m) was perfused into a cat heart Langendorff preparation until a maximum positive inotropic response was obtained. Ouabain (9.6×10-7 m), increased frequency of stimulation, an ionophore RO2-2985 (X537A) and "high" calcium were used to obtain similar increases in force of contraction. TnI was rapidly purified and the phosphate to protein ratios were determined. While isoproterenol, ouabain, calcium, RO2-2985 (RO) and increased frequency produced positive inotropy, only isoproterenol and RO effected an increase in protein-bound phosphate associated with TnI. It was concluded that isoproterenol and RO, but not other perturbations, stimulate phosphorylation of TnI. It is clear from the data, therefore, that phosphorylation of TnI may not be an obligatory requirement for positive inotropy.

Original languageEnglish (US)
Pages (from-to)693-698
Number of pages6
JournalJournal of Molecular and Cellular Cardiology
Issue number8
StatePublished - Aug 1977



  • Calcium
  • Cyclic AMP
  • Force-frequency
  • Ionophore
  • Isoproterenol
  • Kinase
  • Ouabain
  • Phosphorylation
  • Positive inotropy
  • RO2-2985 (X537A)
  • Troponin I

ASJC Scopus subject areas

  • Molecular Biology
  • Cardiology and Cardiovascular Medicine

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