Ty. Gao et al., CAMP-DEPENDENT REGULATION OF CARDIAC L-TYPE CA2+ CHANNELS REQUIRES MEMBRANE TARGETING OF PKA AND PHOSPHORYLATION OF CHANNEL SUBUNITS, Neuron, 19(1), 1997, pp. 185-196
The cardiac L-type Ca2+ channel is a textbook example of an ion channe
l regulated by protein phosphorylation; however, the molecular events
that underlie its regulation remain unknown. Here, we report that in t
ransiently transfected HEK293 cells expressing L-type channels, elevat
ions in cAMP resulted in phosphorylation of the alpha(1C) and beta(2a)
channel subunits and increases in channel activity. Channel phosphory
lation and regulation were facilitated by submembrane targeting of pro
tein kinase A (PKA), through association with an A-kinase anchoring pr
otein called AKAP79. In transfected cells expressing a mutant AKAP79 t
hat is unable to bind PKA, phosphorylation of the alpha(1C) subunit an
d regulation of channel activity were not observed. Furthermore, we ha
ve demonstrated that the association of an AKAP with PKA was required
for beta-adrenergic receptor-mediated regulation of L-type channels in
native cardiac myocytes, illustrating that the events observed in the
heterologous expression system reflect those occurring in the native
system. Mutation of Ser1928 to alanine in the C-terminus of the alpha(
1C) subunit resulted in a complete loss of cAMP-mediated phosphorylati
on and a loss of channel regulation. Thus, the PKA-mediated regulation
of L-type Ca2+ channels is critically dependent on a functional AKAP
and phosphorylation of the alpha(1C) subunit at Ser1928.