Characterization of the defective calpain-endogenous calpain inhibitor system in erythrocytes from Milan hypertensive rats.
In mature red cells of rats from Milan normal (MNS) and hypertensive strains (MHS), the soluble Ca2+ dependent neutral proteinase (calpain) is present in similar amounts with identical Mr of 110 kDa and a dimeric structure composed of two unequal subunits of Mr of 84 and 26 kDa. Conversely, the amount of the endogenous inhibitor is now confirmed by analysis of the specific activity to be approximately 10 times less in red cells of MHS rats. The inhibitor is present in red cells of both strains in three different oligomeric forms of Mr of 240, 120 and 64 kDa. This last molecular species corresponds to the single basic constituent subunit which is the reacting inhibitor form. The apparent equilibrium between the three oligomeric structures is Ca2+-dependent. The high (0.1 mM) Ca2+ requirement for the activity of calpain from erythrocytes of both strains is reduced to 1-5 microM in the presence of plasma membrane phospholipids. Activation of the enzyme in these conditions is prevented by the natural inhibitor. These results strongly support and further emphasize the hypothesis that the structural and functional abnormalities in MHS rats red cells result from an impairment in the modulation of intracellular calpain activity by interaction with its endogenous inhibitor.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors* / Q000097:blood; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004912:Erythrocytes / Q000032:analysis*; D006973:Hypertension / Q000097:blood*; D008970:Molecular Weight; D010743:Phospholipids / Q000494:pharmacology; D051381:Rats
D010743:Phospholipids; D002154:Calpain; D002118:Calcium