Protein kinase A-activated chloride channel is inhibited by the Ca(2+)-calmodulin complex in cardiac sarcoplasmic reticulum.
Cardiac sarcoplasmic reticulum (SR) has several chloride (Cl-) channels, which may neutralize the charge across the SR membrane generated by Ca2+ movement. We recently reported a novel 116-picosiemen Cl- channel that is activated by protein kinase A-dependent phosphorylation in cardiac SR. This Cl- channel may serve as a target protein in the receptor-dependent regulation of cardiac excitation-contraction coupling. To understand further regulatory mechanisms, the effects of Ca2+ on the Cl- channel were studied using the planar lipid bilayer-vesicle fusion technique. In the presence of calmodulin (CaM, 0.1 mumol/L per microgram SR vesicles), Ca2+ (3 mumol/L to 1 mmol/L) added to the cis solution reduced the channel openings in a concentration-dependent fashion, whereas Ca2+ (1 nmol/L to 1 mmol/L) alone or CaM (0.1 to 1 mumol/L per microgram SR vesicles) with 1 nmol/L Ca2+ did not affect the channel activity. This inhibitory effect of Ca2+ in the presence of CaM was prevented by CaM inhibitors N-(6 aminohexyl)-5-chloro-1-naphthalenesulfonamide and calmidazolium but not by CaM kinase II inhibitor KN62. These results suggest that the Ca(2+)-CaM complex itself, but not CaM kinase II, is involved in this channel inhibition. Thus, the cardiac SR 116-picosiemen Cl- channel is regulated not only by protein kinase A-dependent phosphorylation but also by the cytosolic Ca(2+)-CaM complex. This is a novel second messenger-mediated regulation of Cl- channels in cardiac SR membrane.
Kawano
S
S
Department of Cardiovascular Disease, Tokyo Medical and Dental University, Japan.
Hiraoka
M
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D018118:Chloride Channels; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000187:drug effects* / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013267:Stilbenes / Q000494:pharmacology; D013552:Swine
D002147:Calmodulin; D018118:Chloride Channels; D008565:Membrane Proteins; D013267:Stilbenes; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D011494:Protein Kinases; D002118:Calcium