Calmodulin regulation of excitation-contraction coupling in cardiac myocytes.
Calmodulin (CaM) as a ubiquitous Ca2+ sensor interacts with multiple key molecules involved in excitation-contraction (EC) coupling. In the present study, we report that adenoviral expression of a mutant CaM lacking all of its four Ca2+-binding sites, CaM(1-4), at a level 6.5-fold over endogenous CaM markedly increases the amplitude and abbreviates the decay time of Ca2+ transients and contraction in cultured rat ventricular myocytes. To determine the underlying mechanisms, we examined the properties of L-type Ca2+ channels, Ca2+/CaM-dependent protein kinase II (CaMKII), and phospholamban (PLB) in the sarcoplasmic reticulum (SR). We found that CaM(1-4) expression markedly augmented L-type Ca2+ current amplitude and slowed its inactivation. Surprisingly, overexpression of CaM(1-4) increased CaMKII activity and phosphorylation of PLB-Thr-17. Moreover, CaM(1-4) elevated diastolic Ca2+ and caffeine-labile Ca2+ content of the SR. Inhibition of CaMKII by KN-93 or a myristoylated autocamtide-2 related inhibitory peptide prevented the aforementioned PLB phosphorylation and reversed the positive inotropic and relaxant effects, indicating that CaMKII is essential to CaM(1-4) actions. These results demonstrate that CaM modulates Ca2+ influx, SR Ca2+ release, and Ca2+ recycling during cardiac EC coupling. A novel finding of this study is that expression of a Ca2+-insensitive CaM mutant can lead to activation of CaMKII in cardiac myocytes.
Yang
Dongmei
D
National Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing, China.
Song
Long-Sheng
LS
Zhu
Wei-Zhong
WZ
Chakir
Khalid
K
Wang
Wei
W
Wu
Caihong
C
Wang
Yibin
Y
Xiao
Rui-Ping
RP
Chen
S R Wayne
SR
Cheng
Heping
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002147:Calmodulin / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D009154:Mutation; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000099211:Phospholamban
D002118:Calcium; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin; D000099211:Phospholamban