Identification and subcellular localization of the subunits of L-type calcium channels and adenylyl cyclase in cardiac myocytes.
The properties of cardiac L-type channels have been well characterized electrophysiologically, and many such studies have demonstrated that the channels are regulated by a cAMP-dependent pathway. However, the subunit composition of native cardiac L-type calcium channels has not been completely defined. Furthermore, a very important question exists regarding the status of the C-terminal domain of the pore-forming alpha1 subunit, as this domain has the potential to be the target of protein kinases but may be truncated as a result of post-translational processing. In the present studies, the alpha1C and beta2 subunits were identified by subunit-specific antibodies after partial purification from heart membranes, or immunoprecipitation from cardiac myocytes. Both the beta2 and the full-length alpha1C subunits were found to be expressed and co-localized in intact cardiac myocytes along T-tubule membranes. Using a quantitative antibody binding analysis, we demonstrated that the majority of the alpha1C subunits in intact cardiac myocytes appear to be full-length. In addition, we observed that adenylyl cyclase is localized in a pattern similar to the channel subunits in cardiac myocytes. Taken together, our results provide new insights into the structural basis for understanding the regulation of L-type calcium channels by a cAMP-mediated signaling pathway.
Gao
T
T
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611, USA.
Puri
T S
TS
Gerhardstein
B L
BL
Chien
A J
AJ
Green
R D
RD
Hosey
M M
MM
D000262:Adenylyl Cyclases / Q000032:analysis*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000032:analysis* / Q000737:chemistry; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D008297:Male; D008970:Molecular Weight; D009206:Myocardium / Q000737:chemistry* / Q000648:ultrastructure; D011817:Rabbits
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D000262:Adenylyl Cyclases; D002118:Calcium