We aimed to test if stimulation of both
adenosine A2A and A2B receptors is required to produce an effective cardioprotection against
reperfusion injury. Isolated rat hearts were subjected to 30-min regional
ischemia followed by 2 h of reperfusion. The
adenosine A1/A2 receptor agonist 5'-(N-ethylcarboxamido)
adenosine (
NECA) given at reperfusion reduced
infarct size, an effect that was reversed by both the
adenosine A2A antagonist
SCH58261 and the A2B antagonist
MRS1706. The A2B agonist
BAY 60-6583 but not the selective A2A agonist
CGS21680 reduced
infarct size. Interestingly, a combination of
BAY 60-6583 and
CGS21680 further reduced
infarct size. These results suggest that both A2A and A2B receptors are involved in
NECA's anti-
infarct effect at reperfusion.
NECA attenuated mitochondrial swelling upon reperfusion and this was blocked by both
SCH58261 and
MRS1706, indicating that activation of A2 receptors with
NECA can modulate reperfusion-induced
mitochondrial permeability transition pore (mPTP) opening. In support,
NECA also prevented
oxidant-induced loss of mitochondrial membrane potential (DeltaPsi(m)) and matrix Ca2+ overload in cardiomyocytes via both the A2 receptors. In addition,
NECA increased mitochondrial
glycogen synthase kinase-3beta (GSK-3beta) phosphorylation upon reperfusion and this was again blocked by
SCH58261 and
MRS1706. In conclusion, A2A and A2B receptors work in concert to prevent
reperfusion injury in rat hearts treated with
NECA.
NECA may protect the heart by modulating the
mPTP opening through inactivating mitochondrial
GSK-3beta. A simultaneous stimulation of A2A and A2B receptors at reperfusion is required to produce a strong cardioprotection against
reperfusion injury.