Run-down of L-type Ca2+ channels occurs on the alpha 1 subunit.
Run-down of L-type Ca2+ channels in CHO cells stably expressing alpha 1c, alpha 1c beta 1a, or alpha 1c beta 1a alpha 2 delta gamma subunits was studied using the patch-clamp technique (single channel recording). The channel activity (NPo) of alpha 1c channels was increased 4- and 8-fold by coexpression with beta 1a and beta 1a alpha 2 delta gamma, respectively. When membranes containing channels composed of different subunits were excised into basic internal solution, the channel activity exhibited run-down, the time-course of which was independent of the subunit composition. The run-down was restored by the application of calpastatin (or calpastatin contained in cytoplasmic P-fraction) + H-fraction (a high molecular mass fraction of bovine cardiac cytoplasm) + 3 mM ATP, which has been shown to reverse the run-down in native Ca2+ channels in the guinea-pig heart. The restoration level was 64.7, 63.5, and 66.4% for channels composed of alpha 1c, alpha 1c beta 1a, and alpha 1c beta 1a alpha 2 delta gamma, respectively, and was thus also independent of the subunit composition. We conclude that run-down of L-type Ca2+ channels occurs via the alpha 1 subunit and that the cytoplasmic factors maintaining Ca2+ channel activity act on the alpha 1 subunit.
Hao
L Y
LY
Department of Physiology, Faculty of Medicine, Kagoshima University, Japan.
Kameyama
A
A
Kuroki
S
S
Nishimura
S
S
Kameyama
M
M
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D016466:CHO Cells / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins / Q000494:pharmacology; D002417:Cattle; D006224:Cricetinae; D003593:Cytoplasm / Q000737:chemistry; D009206:Myocardium / Q000737:chemistry; D018408:Patch-Clamp Techniques
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C033668:calpastatin; D000255:Adenosine Triphosphate