Calpastatin domain L is involved in the regulation of L-type Ca2+ channels in guinea pig cardiac myocytes.
We have found previously that L-type Ca2+ channel run-down in cell-free patches is partially (10-28%) reversed by calpastatin (CS) and have suggested that CS, an endogenous inhibitor of calpain, has a Ca2+-channel-regulating function. CS is composed of repetitive domains 1-4 (calpain-inhibitory domain) and domain L (a domain whose function is unknown). We therefore investigated which domain of CS was involved in the regulation of Ca2+ channel activity in guinea pig cardiac myocytes using the patch-clamp technique. After the patches were excised into inside-out mode in basic internal solution, the Ca2+ channel activity ran down to 0.45% of the control level recorded in the cell-attached mode. Application of human recombinant full-length CS (25 microM) and domain L (25 microM) restored the Ca2+ channel activity to 13 and 19% of the control level, respectively, while the channel activity was not restored by CS domain 1 (25 microM) (0.66%). Mouse CS domain XLL (25 microM), a complex of domain XL and domain L, restored the calcium channel activity to 11% of the control level. These results suggested that the Ca2+ channel-regulating function of CS is located in domain L. This study is the first description of the function of CS domain L.
Hao
L Y
LY
Department of Physiology, Faculty of Medicine, Kagoshima University, Sakuragaoka 8-35-1, Kagoshima, 890-8520, Japan.
Kameyama
A
A
Kuroki
S
S
Takano
J
J
Takano
E
E
Maki
M
M
Kameyama
M
M
D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D006168:Guinea Pigs; D006801:Humans; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; C033668:calpastatin