抄録
L-type Ca2+ channel activity is diminished in inside-out patches (run-down). We have previously reported that calmodulin (CaM) and calpastatin (CS, an endogenous inhibitor of Ca2+ activated protease, calpain) recover channel activity. CaM can produce channel activity of more than 100% of control, whereas CS domain L (CSL), the effective region of CS, produces channel activity of ∼20% of control. However, interactions between CaM and CSL have not yet been investigated. In this study, we recorded the channel activity in the presence of both CaM and CSL using inside-out patch-clamp technique in guinea-pig cardiac myocytes. Unexpectedly, the channel activity recovered by 1 μM CaM was suppressed by 10 μM CSL (inhibition 78.3%). This inhibition was consistent with a model, in which CSL acted as a partial agonist for the CaM binding site. We also examined the interaction between CaM and CSL in binding to the channel by pull-down assay using GST fusion peptides derived from the intracellular regions of the channel. CaM and CSL competed for the same binding site located in the C-terminal proximal region. These results suggested that CSL and CaM competitively interact at a site in the channel and thereby modulate the channel activity. [J Physiol Sci. 2007;57 Suppl:S228]
