Calpain may produce a Ca(2+)-independent form of kinase C in long-term potentiation

Both an enhancement of Ca 2+ -independent kinase activity in the supernatant fraction and enhanced breakdown of type β kinase C (PKC-β) were observed in the hippocampus after induction of tetanus-induced long-term potentiation (LTP) in the hippocampal CA1 region of rat. The enhanced activity was inhibited by the PKC-specific inhibitor, PKC 19–36 . Both phenomena were also observed simultaneously in the in vitro model system in which hippocampal homogenate was treated with CaCl 2 , and both enhancements were inhibited by the addition of calpain inhibitors, leupeptin and benzyloxycarbonyl-Leu-Met-H. The results suggest that Ca 2+ -independent kinase activity enhanced in the supernatant fraction during LTP derives from the catalytic fragment of PKC-β released by calpain.