It is becoming clear that
stress proteins play a role in various aspects of postischemic myocardial recovery and that the cytoskeleton of cardiac myocytes is an important determinant for cellular survival during
ischemia and energy depletion. In the present study, we addressed the question of whether the cytoskeleton-binding
stress protein alpha B-crystallin may be involved in early cellular responses of rat and porcine myocardium to
ischemia. Immunostaining and subcellular fractionation revealed a rapid
ischemia-induced redistribution of
alpha B-crystallin from a cytosolic pool to intercalated disks and Z lines of the myofibrils. This striking translocation of
alpha B-crystallin from the cytosol to sites of the myofibrillar system that are known to be sensitive to
ischemia-reperfusion injury was accompanied by a rapid shift of a fraction of
alpha B-crystallin to a more acidic isoelectric point. This shift is caused by
alpha B-crystallin phosphorylation, as identified by its augmentation in the presence of
phosphatase inhibitors (
vanadate,
fluoride) and comigration of the acidic
alpha B-crystallin form with the phosphorylated B1 form of lenticular
alpha B-crystallin. In view of the chaperone-like function of
alpha B-crystallin in conjunction with its high level of constitutive expression in the myocardium (1-2% of soluble
protein content), we consider
alpha B-crystallin an excellent candidate to play a role in early aspects of the protection of the myocardial contractile apparatus against
ischemia-reperfusion injury.