Acute
myocardial ischemia maintained for 30 and 60 min with subsequent reperfusion did not induced alterations in the
cyclic AMP-mediated phosphorylation capacity of
phospholamban and
troponin I. Inotropic stimulation of the normal heart with 0.1/uM
isoprenaline for 2 min resulted in a simultaneous P-incorporation into
phospholamban and
troponin I to 44.4 +/- 7.5 pmoles P/mg
protein and 42.4 +/- 2.9 pmoles P/mg
protein, respectively, assayed by a standardized back-phosphorylation procedure. The
adrenergic responsiveness, however, was markedly reduced in the time course of
ischemia. After an ischemic period of 60 min the
adrenergic-stimulated phosphorylation of
phospholamban was diminished to 41 per cent of the control value, whereas the increase of
troponin I phosphorylation was completely lost. This differential effect can be discussed in terms of the existence of cytosolic compartments for cA, possessing different lability to ischemic injury of cardiac cells. After post-ischemic reperfusion the
isoprenaline responsiveness of the phosphorylation of
phospholamban and
troponin I was found to be normal demonstrating a reversibility at the level of two important regulator
proteins, if the transient
ischemia do not exceed 60 min period.