Recent studies suggest that
p38 mitogen-activated protein kinase (MAPK) may be involved in ischemic preconditioning (PC). To further test this possibility, the regulation of MAPK-activated
protein kinase 2 (
MAPKAPK2), a
kinase immediately downstream from
p38 MAPK, and the activity of c-Jun NH(2)-terminal
kinase (JNK), a second MAPK, were examined in preconditioned hearts. Isolated, perfused rabbit hearts were subjected to 20 to 30 minutes of global
ischemia. Ventricular biopsies before treatment and after 20 minutes of
ischemia were homogenized, and the activities of
MAPKAPK2 and JNK were evaluated. For the
MAPKAPK2 experiments, 7 groups were studied, as follows: control hearts; preconditioned hearts; hearts treated with 500 nmol/L R(-) N(6)-(2-phenylisopropyl)
adenosine (PIA), an A(1)-adenosine receptor agonist; preconditioned hearts pretreated with 100 micromol/L 8-(p-sulfophenyl)
theophylline (SPT), an
adenosine receptor antagonist; preconditioned hearts also treated with
SB 203580, a potent inhibitor of
p38 MAPK activation; hearts treated with 50 ng/mL
anisomycin (a
p38 MAPK/JNK activator); and hearts treated with both
anisomycin (50 ng/mL) and the
tyrosine kinase inhibitor genistein (50 micromol/L).
MAPKAPK2 activity was not altered in control hearts after 20 minutes of global
ischemia. By contrast, there was a 3.8-fold increase in activity during
ischemia in preconditioned hearts. Activation of
MAPKAPK2 in preconditioned hearts was blocked by both SPT and
SB 203580.
MAPKAPK2 activity during
ischemia increased 3.5-fold and 3.3-fold in hearts pretreated with PIA or
anisomycin, respectively.
MAPKAPK2 activation during
ischemia in hearts pretreated with
anisomycin was blocked by
genistein. In separate hearts,
anisomycin mimicked the anti-
infarct effect of PC, and that protection was abolished by
genistein. JNK activity was measured in control and preconditioned hearts. There was a comparable, modest decline in activity during 30 minutes of global
ischemia in both groups. As a positive control, a third group of hearts was treated with
anisomycin before global
ischemia, and in these, JNK activity increased by 290% above baseline. These results confirm that the
p38 MAPK/
MAPKAPK2 pathway is activated during
ischemia only if the heart is in a preconditioned state. These data further support
p38 MAPK as an important signaling component in ischemic PC.