Na+ channel regulation by Ca2+/calmodulin and Ca2+/calmodulin-dependent protein kinase II in guinea-pig ventricular myocytes.
OBJECTIVE
Calmodulin (CaM) regulates Na+ channel gating through binding to an IQ-like motif in the C-terminus. Ca2+/CaM-dependent protein kinase II (CaMKII) regulates Ca2+ handling, and chronic overactivity of CaMKII is associated with left ventricular hypertrophy and dysfunction and lethal arrhythmias. However, the acute effects of Ca2+/CaM and CaMKII on cardiac Na+ channels are not fully understood.


RESULTS
Purified Na(V)1.5-glutathione-S-transferase fusion peptides were phosphorylated in vitro by CaMKII predominantly on the I-II linker. Whole-cell voltage-clamp was used to measure Na+ current (I(Na)) in isolated guinea-pig ventricular myocytes in the absence or presence of CaM or CaMKII in the pipette solution. CaMKII shifted the voltage dependence of Na+ channel availability by approximately +5 mV, hastened recovery from inactivation, decreased entry into intermediate or slow inactivation, and increased persistent (late) current, but did not change I(Na) decay. These CaMKII-induced changes of Na+ channel gating were completely abolished by a specific CaMKII inhibitor, autocamtide-2-related inhibitory peptide (AIP). Ca2+/CaM alone reproduced the CaMKII-induced changes of I(Na) availability and the fraction of channels undergoing slow inactivation, but did not alter recovery from inactivation or the magnitude of the late current. Furthermore, the CaM-induced changes were also completely abolished by AIP. On the other hand, cAMP-dependent protein kinase A inhibitors did not abolish the CaM/CaMKII-induced alterations of I(Na) function.


CONCLUSIONS
Ca2+/CaM and CaMKII have distinct effects on the inactivation phenotype of cardiac Na+ channels. The differences are consistent with CaM-independent effects of CaMKII on cardiac Na+ channel gating.
Division of Cardiology, Johns Hopkins University School of Medicine, 720 Rutland Ave., Ross 844, Baltimore, MD 21205, USA.
Takeshi
T
Aiba
Geoffrey G
GG
Hesketh
Ting
T
Liu
Rachael
R
Carlisle
Maria Celeste
MC
Villa-Abrille
Brian
B
O'Rourke
Fadi G
FG
Akar
Gordon F
GF
Tomaselli
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D006168:Guinea Pigs; D015640:Ion Channel Gating / Q000502:physiology; D010766:Phosphorylation; D015222:Sodium Channels / Q000502:physiology*
D002147:Calmodulin; D015222:Sodium Channels; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium