Xg. Zong et al., ON THE REGULATION OF THE EXPRESSED L-TYPE CALCIUM-CHANNEL BY CAMP-DEPENDENT PHOSPHORYLATION, Pflugers Archiv, 430(3), 1995, pp. 340-347
The Ca2+ channel subunits alpha(1C-a) and alpha(1C-b) were stably expr
essed in Chinese hamster ovary (CHO) and human embryonic kidney (HEK)
293 cells. The peak Ba2+ current (I-Ba) of these cells was not affecte
d significantly by internal dialysis with 0.1 mM cAMP-dependent protei
n kinase inhibitor peptide (mPKI), 25 mu M cAMP-dependent protein kina
se catalytic subunit (PKA), or a combination of 25 mu M PKA and 1 mu M
okadaic acid. The activity of the alpha(1C-b) channel subunit express
ed stably in HEK 293 cells was depressed by 1 mu M H 89 and was not in
creased by superfusion with 5 mu M forskolin plus 20 mu M isobutyl-met
hylxanthine (IBMX). The alpha(1C-b), beta(2), alpha(2)/delta complex w
as transiently expressed in HEK 293 cells; it was inhibited by interna
l dialysis of the cells with 1 mu M H 89, but was not affected by inte
rnal dialysis with mPKI, PKA or microcystin. Internal dialysis of cell
s expressing the alpha(1C-a), beta(2), alpha(2)/delta channel with 10
mu M PKA did not induce facilitation after a 150-ms prepulse to +50 mV
. The Ca2+ current (I-Ca) of cardiac myocytes increased threefold duri
ng internal dialysis with 5 mu M forskolin plus 50 mu M IBMX. These re
sults indicate that the L-type Ca2+ channel expressed is not modulated
by cAMP-dependent phosphorylation to the same extent as in native car
diac myocytes.