Functional Regulation of L-type Calcium Channels via Protein Kinase A-mediated Phosphorylation of the β2 Subunit

Abstract

Activation of protein kinase A (PKA) through the β-adrenergic receptor pathway is crucial for the positive regulation of cardiac L-type currents; however it is still unclear which phosphorylation events cause the robust regulation of channel function. In order to study whether or not the recently identified PKA phosphorylation sites on the β2 subunit are of functional significance, we coexpressed wild-type (WT) or mutant β2 subunits in tsA-201 cells together with an α1C subunit, α1CΔ1905, that lacked the C-terminal 265 amino acids, including the only identified PKA site at Ser-1928. This truncated α1C subunit was similar to the truncated α1C subunit isolated from cardiac tissue not only in size (∼190 kDa), but also with respect to its failure to serve as a PKA substrate. In cells transfected with the WT β2 subunit, voltage-activated Ba2+ currents were significantly increased when purified PKA was included in the patch pipette. Furthermore, mutations of Ser-478 and Ser-479 to Ala, but not Ser-459 to Ala, on the β2 subunit, completely abolished the PKA-induced increase of currents. The data indicate that the PKA-mediated stimulation of cardiac L-type Ca2+currents may be at least partially caused by phosphorylation of the β2 subunit at Ser-478 and Ser-479. Activation of protein kinase A (PKA) through the β-adrenergic receptor pathway is crucial for the positive regulation of cardiac L-type currents; however it is still unclear which phosphorylation events cause the robust regulation of channel function. In order to study whether or not the recently identified PKA phosphorylation sites on the β2 subunit are of functional significance, we coexpressed wild-type (WT) or mutant β2 subunits in tsA-201 cells together with an α1C subunit, α1CΔ1905, that lacked the C-terminal 265 amino acids, including the only identified PKA site at Ser-1928. This truncated α1C subunit was similar to the truncated α1C subunit isolated from cardiac tissue not only in size (∼190 kDa), but also with respect to its failure to serve as a PKA substrate. In cells transfected with the WT β2 subunit, voltage-activated Ba2+ currents were significantly increased when purified PKA was included in the patch pipette. Furthermore, mutations of Ser-478 and Ser-479 to Ala, but not Ser-459 to Ala, on the β2 subunit, completely abolished the PKA-induced increase of currents. The data indicate that the PKA-mediated stimulation of cardiac L-type Ca2+currents may be at least partially caused by phosphorylation of the β2 subunit at Ser-478 and Ser-479. protein kinase A wild-type farad(s) A-kinase-anchoring protein It has been known for more than a decade that the cardiac L-type calcium channel is an important effector for positive modulation of cardiac contractility through signaling cascades initiated by activation of the β-adrenergic receptors (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google Scholar). It is well accepted that activation of protein kinase A (PKA)1 through the βAR pathway is crucial for the positive regulation of cardiacl-type Ca2+ currents (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google Scholar). Cardiac L-type Ca2+ channels are composed of α1C,β2, and α2δ subunits (2De Waard M. Gurnett C.A. Campbell K.P. Narahashi T. Ion Channels. 4. Plenum Press, New York1996: 41-87Google Scholar, 3Hosey M.M. Chien A.J. Puri T.S. Trends Cardiovasc. Med. 1996; 6: 265-273Crossref PubMed Scopus (47) Google Scholar), and both the α1C and β2 subunits have been demonstrated to be direct targets of PKA-mediated phosphorylation (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google Scholar, 5Mitterdorfer J. Froschmayr M. Grabner M. Moebius F.F. Glossmann H. Striessnig J. Biochemistry. 1996; 35: 9400-9406Crossref PubMed Scopus (82) Google Scholar, 6Gao T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, T.S. M.M. Biochemistry. PubMed Scopus Google Scholar). it has been to the phosphorylation of of subunits to functional regulation of the channels in cells and to of the sites of phosphorylation to functional in channel in cardiac are to the of channel in have the to the of subunit phosphorylation in the regulation of the a with is that it has been to in the robust regulation of L-type channels that is in cardiac cells J. A. A. J. Physiol. PubMed Scopus Google phosphorylation and functional regulation of the channels was in cells when the channels were coexpressed with the protein kinase and T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, Scott J.D. J. PubMed Scopus Google Scholar). both the α1C and β2 subunits were when coexpressed with only phosphorylation of in the α1C subunit to be to channel regulation T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). with the robust PKA-mediated stimulation of L-type currents in the of PKA in the in the of were increase in T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, Scott J.D. J. PubMed Scopus Google Scholar). In is in a of the of the α1C subunit that to be to in M.M. J. PubMed Google Scholar, T. Puri T.S. Chien A.J. Green M.M. J. PubMed Scopus Google Scholar), the that site may not be to PKA-mediated regulation in cardiac This that as phosphorylation of the subunit, may a functional in channel This of study was to whether or not PKA phosphorylation of the β2 subunit has functional The β2 subunit has been to phosphorylation at sites in and in cardiac and H. PubMed Scopus Google Scholar, H. S. 1996; PubMed Scopus Google Scholar, Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). the subunit has at and that serve as PKA sites are not by PKA Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). the sites of PKA-mediated phosphorylation on the subunit are and Ser-479 Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). of study was to of sites functional in channel In order to from the identified PKA phosphorylation site on the α1C subunit and to that may in we a mutant of the α1C subunit, α1CΔ1905, that lacked the C-terminal 265 amino acids, including the only identified PKA site at PKA channels a α1C The we was whether or not PKA cardiac L-type calcium channels of a wild-type β2 subunit and a truncated that the site that was to be both in (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google Scholar, 5Mitterdorfer J. Froschmayr M. Grabner M. Moebius F.F. Glossmann H. Striessnig J. Biochemistry. 1996; 35: 9400-9406Crossref PubMed Scopus (82) Google and in cells T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). The truncated α1C subunit in a that in the of its of This mutant subunit a similar when by as the truncated α1C subunit isolated from cardiac tissue was not a for PKA that is the site by PKA in the α1C subunit (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). through channels of and WT β2 subunits were in to to The the of Ba2+ currents through L-type channels regulation of L-type calcium currents. the of through L-type calcium channels in cells with the truncated and the WT from a in to of with or PKA in the are for the from cells from in the or of PKA in the are order to the of PKA on the purified subunit of PKA was to the patch at a of This in an increase to at in of the Ba2+ by the channels by the and the WT subunits A and demonstrated that PKA cause in currents from channels a α1C In the increase in that in cardiac the in the of the Ba2+ was This is in cardiac order to whether or not the PKA-mediated increase in Ba2+ currents was to phosphorylation of the subunit, we the subunit with mutant subunits that lacked the identified PKA phosphorylation sites Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). mutations of to at or Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). Ba2+ currents in cells and were from currents in cells the WT β2 subunit that not the functional of the The of the subunit of PKA to the patch caused a increase in Ba2+ currents with the at in cells and the mutant A and This was with that with the WT subunit with In and in to the with the WT subunit, a of the that caused activation of calcium channels from to was in to PKA by of activation stimulation of through channels phosphorylation site Ser-459 on the in to from cells with the subunit with or PKA in the data for the of from similar as in channels by and also currents that were similar in and to with the WT subunit in the of PKA with that mutations not to of the subunit in to was with the WT and mutant the of PKA to the not currents with and the subunit at have demonstrated that Ser-478 and Ser-479 are for phosphorylation by PKA and that of to a in the PKA-mediated phosphorylation of the β2 together with the that the subunit was not a for the functional of the PKA-mediated regulation in the are to through phosphorylation of the demonstrated the of phosphorylation of the to the regulation of the cardiac calcium channel and identified the important in the β2 subunit that are important for channel of PKA-mediated stimulation of L-type calcium channels in cells were as for the subunits of WT currents in to with or PKA in the data for the for voltage-activated in the or of PKA in the regulation of the cardiac L-type calcium channel by activation of PKA has been well through (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google however the phosphorylation have not been In the for PKA that are for the stimulation of the calcium in cardiac are The together with in T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, T.S. M.M. Biochemistry. PubMed Scopus Google Scholar, Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar), and that the regulation of the channel may through more than in PKA-mediated stimulation of the cardiac L-type channel in J. A. A. J. Physiol. PubMed Scopus Google Scholar), we have of that for of the PKA In with α1C and be only the channels are with an T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the were to phosphorylation of in the of the α1C subunit, as of site to a of the PKA T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the PKA-mediated phosphorylation of in the α1C subunit was phosphorylation of the subunit was not T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). the was at sites when it was coexpressed with the α1C subunit in the or of an not to be a functional of the phosphorylation of the T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). in the in were but a in the was T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the in with a α1C subunit, we have demonstrated the functional of the phosphorylation of sites at Ser-478 and Ser-479 in the β2 subunit for regulation of the channel in to In the increase in was more than in the but a in the was only in the of the not the of an in with the that the phosphorylation whether or not it was with an to of regulation of the cardiac L-type in that the subunit may be in the are to whether or or events to the PKA-mediated regulation of the channels in both the in and the in the that are in cardiac it is that both to regulation in the to of regulation in cardiac is to the and of the α1C It is that the of the is to for of the functional of PKA-mediated phosphorylation of the and that regulation through a when the α1C subunit is the of regulation of the channel may be the α1C subunit is in cells and the C-terminal with the of the This is by the that of the α1C subunit to be truncated at the when isolated from that the is in cardiac in and with the α1C and β2 subunits T. Puri T.S. Chien A.J. Green M.M. J. PubMed Scopus Google Scholar). the of the may of the channel to and the functional of the phosphorylation of both the α1C and β2 of channel regulation and the of regulation that in It has been known for more than a decade that the cardiac L-type calcium channel is an important effector for positive modulation of cardiac contractility through signaling cascades initiated by activation of the β-adrenergic receptors (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google Scholar). It is well accepted that activation of protein kinase A (PKA)1 through the βAR pathway is crucial for the positive regulation of cardiacl-type Ca2+ currents (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google Scholar). Cardiac L-type Ca2+ channels are composed of α1C,β2, and α2δ subunits (2De Waard M. Gurnett C.A. Campbell K.P. Narahashi T. Ion Channels. 4. Plenum Press, New York1996: 41-87Google Scholar, 3Hosey M.M. Chien A.J. Puri T.S. Trends Cardiovasc. Med. 1996; 6: 265-273Crossref PubMed Scopus (47) Google Scholar), and both the α1C and β2 subunits have been demonstrated to be direct targets of PKA-mediated phosphorylation (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google Scholar, 5Mitterdorfer J. Froschmayr M. Grabner M. Moebius F.F. Glossmann H. Striessnig J. Biochemistry. 1996; 35: 9400-9406Crossref PubMed Scopus (82) Google Scholar, 6Gao T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, T.S. M.M. Biochemistry. PubMed Scopus Google Scholar). it has been to the phosphorylation of of subunits to functional regulation of the channels in cells and to of the sites of phosphorylation to functional in channel in cardiac are to the of channel in have the to the of subunit phosphorylation in the regulation of the a with is that it has been to in the robust regulation of L-type channels that is in cardiac cells J. A. A. J. Physiol. PubMed Scopus Google Scholar). phosphorylation and functional regulation of the channels was in cells when the channels were coexpressed with the protein kinase and T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, Scott J.D. J. PubMed Scopus Google Scholar). both the α1C and β2 subunits were when coexpressed with only phosphorylation of in the α1C subunit to be to channel regulation T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). with the robust PKA-mediated stimulation of L-type currents in the of PKA in the in the of were increase in T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, Scott J.D. J. PubMed Scopus Google Scholar). In is in a of the of the α1C subunit that to be to in M.M. J. PubMed Google Scholar, T. Puri T.S. Chien A.J. Green M.M. J. PubMed Scopus Google Scholar), the that site may not be to PKA-mediated regulation in cardiac This that as phosphorylation of the subunit, may a functional in channel This of study was to whether or not PKA phosphorylation of the β2 subunit has functional The β2 subunit has been to phosphorylation at sites in and in cardiac and H. PubMed Scopus Google Scholar, H. S. 1996; PubMed Scopus Google Scholar, Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). the subunit has at and that serve as PKA sites are not by PKA Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). the sites of PKA-mediated phosphorylation on the subunit are and Ser-479 Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). of study was to of sites functional in channel In order to from the identified PKA phosphorylation site on the α1C subunit and to that may in we a mutant of the α1C subunit, α1CΔ1905, that lacked the C-terminal 265 amino acids, including the only identified PKA site at Ser-1928. PKA channels a α1C The we was whether or not PKA cardiac L-type calcium channels of a wild-type β2 subunit and a truncated that the site that was to be both in (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google Scholar, 5Mitterdorfer J. Froschmayr M. Grabner M. Moebius F.F. Glossmann H. Striessnig J. Biochemistry. 1996; 35: 9400-9406Crossref PubMed Scopus (82) Google and in cells T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). The truncated α1C subunit in a that in the of its of This mutant subunit a similar when by as the truncated α1C subunit isolated from cardiac tissue was not a for PKA that is the site by PKA in the α1C subunit (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). through channels of and WT β2 subunits were in to to The the of Ba2+ currents through L-type channels order to the of PKA on the purified subunit of PKA was to the patch at a of This in an increase to at in of the Ba2+ by the channels by the and the WT subunits A and demonstrated that PKA cause in currents from channels a α1C In the increase in that in cardiac the in the of the Ba2+ was This is in cardiac order to whether or not the PKA-mediated increase in Ba2+ currents was to phosphorylation of the subunit, we the subunit with mutant subunits that lacked the identified PKA phosphorylation sites Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). mutations of to at or Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). Ba2+ currents in cells and were from currents in cells the WT β2 subunit that not the functional of the The of the subunit of PKA to the patch caused a increase in Ba2+ currents with the at in cells and the mutant A and This was with that with the WT subunit with In and in to the with the WT subunit, a of the that caused activation of calcium channels from to was in to PKA by of activation stimulation of through channels phosphorylation site Ser-459 on the in to from cells with the subunit with or PKA in the data for the of from similar as in channels by and also currents that were similar in and to with the WT subunit in the of PKA with that mutations not to of the subunit in to was with the WT and mutant the of PKA to the not currents with and the subunit at have demonstrated that Ser-478 and Ser-479 are for phosphorylation by PKA and that of to a in the PKA-mediated phosphorylation of the β2 together with the that the subunit was not a for the functional of the PKA-mediated regulation in the are to through phosphorylation of the demonstrated the of phosphorylation of the to the regulation of the cardiac calcium channel and identified the important in the β2 subunit that are important for channel of PKA-mediated stimulation of L-type calcium channels in cells were as for the subunits of WT currents in to with or PKA in the data for the for voltage-activated in the or of PKA in the PKA channels a α1C The we was whether or not PKA cardiac L-type calcium channels of a wild-type β2 subunit and a truncated that the site that was to be both in (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google Scholar, 5Mitterdorfer J. Froschmayr M. Grabner M. Moebius F.F. Glossmann H. Striessnig J. Biochemistry. 1996; 35: 9400-9406Crossref PubMed Scopus (82) Google and in cells T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). The truncated α1C subunit in a that in the of its of This mutant subunit a similar when by as the truncated α1C subunit isolated from cardiac tissue was not a for PKA that is the site by PKA in the α1C subunit (4De Jongh K.S. Murphy B.J. Colvin A.A. Hell J.W. Takahashi M. Catterall W.A. Biochemistry. 1996; 35: 10392-103402Crossref PubMed Scopus (239) Google T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). through channels of and WT β2 subunits were in to to The the of Ba2+ currents through L-type channels In order to the of PKA on the purified subunit of PKA was to the patch at a of This in an increase to at in of the Ba2+ by the channels by the and the WT subunits A and demonstrated that PKA cause in currents from channels a α1C In the increase in that in cardiac the in the of the Ba2+ was This is in cardiac In order to whether or not the PKA-mediated increase in Ba2+ currents was to phosphorylation of the subunit, we the subunit with mutant subunits that lacked the identified PKA phosphorylation sites Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). mutations of to at or Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar). Ba2+ currents in cells and were from currents in cells the WT β2 subunit that not the functional of the The of the subunit of PKA to the patch caused a increase in Ba2+ currents with the at in cells and the mutant A and This was with that with the WT subunit with In and in to the with the WT subunit, a of the that caused activation of calcium channels from to was in to PKA by of activation The channels by and also currents that were similar in and to with the WT subunit in the of PKA with that mutations not to of the subunit in to was with the WT and mutant the of PKA to the not currents with and the subunit at have demonstrated that Ser-478 and Ser-479 are for phosphorylation by PKA and that of to a in the PKA-mediated phosphorylation of the β2 together with the that the subunit was not a for the functional of the PKA-mediated regulation in the are to through phosphorylation of the demonstrated the of phosphorylation of the to the regulation of the cardiac calcium channel and identified the important in the β2 subunit that are important for channel regulation of the cardiac L-type calcium channel by activation of PKA has been well through (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google however the phosphorylation have not been In the for PKA that are for the stimulation of the calcium in cardiac are The together with in T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, T.S. M.M. Biochemistry. PubMed Scopus Google Scholar, Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar), and that the regulation of the channel may through more than in PKA-mediated stimulation of the cardiac L-type channel in J. A. A. J. Physiol. PubMed Scopus Google Scholar), we have of that for of the PKA In with α1C and be only the channels are with an T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the were to phosphorylation of in the of the α1C subunit, as of site to a of the PKA T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the PKA-mediated phosphorylation of in the α1C subunit was phosphorylation of the subunit was not T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). the was at sites when it was coexpressed with the α1C subunit in the or of an not to be a functional of the phosphorylation of the T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). in the in were but a in the was T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the in with a α1C subunit, we have demonstrated the functional of the phosphorylation of sites at Ser-478 and Ser-479 in the β2 subunit for regulation of the channel in to In the increase in was more than in the but a in the was only in the of the not the of an in with the that the phosphorylation whether or not it was with an to of regulation of the cardiac L-type in that the subunit may be in the are to whether or or events to the PKA-mediated regulation of the channels in both the in and the in the that are in cardiac it is that both to regulation in the to of regulation in cardiac is to the and of the α1C It is that the of the is to for of the functional of PKA-mediated phosphorylation of the and that regulation through a when the α1C subunit is the of regulation of the channel may be the α1C subunit is in cells and the C-terminal with the of the This is by the that of the α1C subunit to be truncated at the when isolated from that the is in cardiac in and with the α1C and β2 subunits T. Puri T.S. Chien A.J. Green M.M. J. PubMed Scopus Google Scholar). the of the may of the channel to and the functional of the phosphorylation of both the α1C and β2 of channel regulation and the of regulation that in The regulation of the cardiac L-type calcium channel by activation of PKA has been well through (1McDonald T.F. Pelzer S. Trautwein W. Pelzer D.J. Physiol. Rev. 1994; 74: 365-507Crossref PubMed Scopus (923) Google however the phosphorylation have not been In the for PKA that are for the stimulation of the calcium in cardiac are The together with in T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar, T.S. M.M. Biochemistry. PubMed Scopus Google Scholar, Puri T.S. Chien A.J. M.M. Biochemistry. PubMed Scopus Google Scholar), and that the regulation of the channel may through more than in PKA-mediated stimulation of the cardiac L-type channel in J. A. A. J. Physiol. PubMed Scopus Google Scholar), we have of that for of the PKA In with α1C and be only the channels are with an T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the were to phosphorylation of in the of the α1C subunit, as of site to a of the PKA T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the PKA-mediated phosphorylation of in the α1C subunit was phosphorylation of the subunit was not T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). the was at sites when it was coexpressed with the α1C subunit in the or of an not to be a functional of the phosphorylation of the T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). in the in were but a in the was T. Yatani A. Dell'Acqua M.L. Sako H. Green S.A. Dascal N. Scott J.D. M.M. PubMed Scopus Google Scholar). In the in with a α1C subunit, we have demonstrated the functional of the phosphorylation of sites at Ser-478 and Ser-479 in the β2 subunit for regulation of the channel in to In the increase in was more than in the but a in the was only in the of the not the of an in with the that the phosphorylation whether or not it was with an to of regulation of the cardiac L-type in that the subunit may be in the are to whether or or events to the PKA-mediated regulation of the channels in both the in and the in the that are in cardiac it is that both to regulation in the to of regulation in cardiac is to the and of the α1C It is that the of the is to for of the functional of PKA-mediated phosphorylation of the and that regulation through a when the α1C subunit is the of regulation of the channel may be the α1C subunit is in cells and the C-terminal with the of the This is by the that of the α1C subunit to be truncated at the when isolated from that the is in cardiac in and with the α1C and β2 subunits T. Puri T.S. Chien A.J. Green M.M. J. PubMed Scopus Google Scholar). the of the may of the channel to and the functional of the phosphorylation of both the α1C and β2 of channel regulation and the of regulation that in the of for the of and and to the of for and