ENERGETIC SUPPORT OF POST-ISCHEMIC CARDIAC PERFORMANCE

Project Details

Description

Contractile function is depressed for prolonged periods in reversibly
injured, viable myocardium following relatively brief coronary
occlusions. Although recognized as an important clinical problem, the
pathophysiological mechanisms of this myocardial 'stunning' are
controversial. We have developed and characterized an isolated working
guinea-pig heart model of stunning. In these hearts, the energy-yielding
substrate pyruvate produces marked, parallel enhancements of ventricular
performance and myocytic energy level (cytosolic ATP phosphorylation
potential and Gibbs free energy of ATP hydrolysis). The overall goal of
this research is to delineate the subcellular mechanisms responsible for
these energy-linked functional improvements. Myocardial function is
controlled in large measure by the Ca2+ pumping activity of the
sarcoplasmic reticulum Ca2+ ATPase. Our preliminary findings indicate
that pyruvate-energization enhances sarcoplasmic reticulum Ca2+_
transport in non-ischemic heart. Project one will test the hypothesis
that cytosolic energization stimulates Ca2+ uptake by sarcoplasmic
reticulum in post-ischemic 'stunned' myocardium. Cytosolic energy level
in 'stunned' guinea-pig hearts will be varied by altering substrate
composition of perfusion media or by beta-adrenergic stimulation with
isoproterenol, and Ca2+ uptake and Ca2+ ATPase activity will be
quantitated in sarcoplasmic reticulum isolated from stop-frozen hearts.
Project two will test the hypothesis that substrate-enhancement of
sarcoplasmic reticular function stems from increased phospholamban
phosphorylation, a well-characterized mechanism for beta-adrenergic
stimulation of cardiac inotropism. To effect radiolabelling of cardiac
phosphoproteins, intramyocytic high-energy phosphate pools will be
labelled by perfusion with [32P]inorganic phosphate; during tracer-free
washout, cardiac inotropism will be increased by pyruvate-energization
or by beta-adrenergic stimulation with isoproterenol. Proteins in
isolated sarcoplasmic reticulum will be separated by electrophoresis, and
32P incorporation detected and quantitated by autoradiography and
scintillation counting.

This investigation will delineate the bioenergetic mechanisms for the
observed highly significant relationship between contractility and
cytosolic energy level in normoxic and especially 'stunned' myocardium
in the absence of adrenergic stimulation. Of special clinical interest,
pyruvate energization may be effective in reversing postischemic
impairment of sarcoplasmic reticulum Ca2+ transport. Since pyruvate,
unlike catecholamines, increases cytosolic energy level, this
investigation may indicate that pyruvate could be a valuable
cardioprotective intervention in clinical situations of energy-depleted
heart.
StatusFinished
Effective start/end date1/08/9331/07/94