Calmodulin prevents the proteolysis of connexin32 by m-calpain

Purified mouse liver gap junctions formed by connexin32 and connexin26 were treated with the low Ca2+-affinity isoform of calpain (m-calpain). This protease proteolyzes connexin32 but not connexin26. However, the binding of calmodulin to connexin32 prevented its proteolysis. Connexin32, but not connexin26, was phosphorylated by protein kinase A, and calmodulin bound to the phosphorylated form of connexin32 also protected the latter against m-calpain-mediated proteolysis. We propose that calmodulin plays a modulatory role on the degradation of connexin32 and hence on the turnover of gap junction channels. (C) 1997 Elsevier Science S.A.