Abstract
Calpastatin, an endogenous inhibitor of calpain, is composed of domain L and four repetitive homologous domains 1–4. Domains 1–4 inhibit calpain, whereas domain L partially reprimes L-type Ca 2+ channels for voltage-gated activation. In the present study, the effects on Ca 2+ channel activity of four isoforms and a series of fragments of calpastatin domain L were investigated in guinea-pig ventricular myocytes with the patch–clamp method. With one exception, all the isoforms and fragment peptides that contained amino acid residues 54–64 of domain L reprimed the Ca 2+ channels to comparable levels (9–15% of control activity) to those observed previously with a full-length form of calpastatin. These results suggest that the region containing amino acid residues 54–64 (EGKPKEHTEPK) is responsible for the Ca 2+ channel repriming function of calpastatin domain L.
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