Calpastatin expression in porcine cardiac and skeletal muscle and partial gene structure

The expression in porcine skeletal and cardiac muscle of calpastatin, the s pecific endogenous inhibitor of the calpain proteolytic system, was examine d 16 h after a single dose of a specific beta (2)-agonist. Immunoblotting o f extracts indicated that treatment increased skeletal calpastatin 135-kDa band intensity (P < 0.01), while in cardiac combined 145- and 135-kDa band intensity decreased (P < 0.05). Treatment increased skeletal (P < 0.01) but not cardiac calpastatin mRNA steady-state levels. Three types of cardiac c alpastatin mRNA transcripts were identified by 5 ' -RACE. Types I and II en coded a putative XL region that originated either from exon 1x(A) or exon 1 x(B), arranged in tandem. Type III predominated in skeletal muscle and orig inated from exon 1u, which was located 40-50 kb 3 ' to exons 1x(A) and 1x(B ). The region 5 ' to exon In may act as an independent promoter regulated b y a cAMP-dependent mechanisms, thereby explaining the differential response of calpastatin to adrenergic stimulation in cardiac and skeletal muscle. ( C) 2001 Academic Press.