抄録
Calpastatin (CS), an endogenous inhibitor of the calcium-activated protease calpain, is composed of N-terminal domain L (CSL) and four repetitive calpain inhibitory domains 1-4, and expressed in virtually all cell types. We have previously found that CS modulates the cardiac CaV1.2 Ca2+ channels in inside-out patch mode of patch-clamp technique in guinea-pig cardiomyocytes and that the Ca2+ channel regulatory function is located in CSL. However, how does CSL modulate the channels activity is not known. In this study, we have determined the interaction site of CSLin the channel by the pull-down binding assay using GST-fused fragment peptides of the α1 subunit. CSL interacted directly with IQ domain of the proximal C-terminal region of α1 subunit (a. a. number of guinea-pig α1: 1648-1672), which is also one of the calmodulin (CaM) binding sites. CSL bound to IQ domain with a higher affinity in the presence of Ca2+ than its absence. CSL binding to IQ also showed a competitive manner with CaM. These results suggest that CSL directly interacts with IQ domain of α1 subunit of the voltage dependant Ca2+ channel and inhibits the CaM binding to this domain. A role of CSL in the regulation of the Ca2+ channels will be discussed. [J Physiol Sci. 2007;57 Suppl:S228]
