title: Constitutive CaMKII activity regulates Na+ channel in rat ventricular myocytes.
abstract: The cardiac voltage-gated Na(+) channel controls the upstroke of action potential and membrane excitability. The Na(+) channel associates with Ca(2+)/CaM-dependent protein kinase (CaMKII), but the role of CaMKII on Na(+) channel activity in the resting state is not clear. In this report, we investigated whether CaMKII constitutively regulates Na(+) currents (I(Na)), independent of Ca(2+) influx in rat ventricular myocytes using patch clamp technique. CaMKII inhibition (by KN93 or autocamtide-related inhibitory peptide) caused a negative shift in I(Na) steady-state inactivation and delayed recovery from slow inactivation, limiting channel availability. The reduction of I(Na) was 29.47+/-3.01% at a holding potential (V(h)) of -120 mV and it increased to 77.70+/-7.92% when V(h) was -70 mV, suggesting that near the resting membrane potential, three-quarters of I(Na) depends on CaMKII action. CaMKII inhibition also enhanced intermediate inactivation, as well as delayed recovery from fast inactivation, and decreased late I(Na). KN92, an inactive analog of KN93, had no effect on I(Na). Using an antibody against phosphorylated (activated) CaMKII, we found that constitutively active CaMKII co-immunoprecipitated with Na(+) channels under resting conditions. CaMKII inhibitors reduced the level of phosphorylated CaMKII, which correlated with the degree of reduction in channel availability. These data suggest that CaMKII in an active form contributes to regulating I(Na). Finally, we observed a drastic reduction in the upstroke velocity of action potentials upon CaMKII inhibition. In conclusion, CaMKII constitutively regulates cardiac Na(+) channel and this regulatory mechanism is important for the maintenance of Na(+) channel characteristics under physiological conditions.
authors: Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, 440-746, South Korea.
authors: Jin-Young
authors: JY
authors: Yoon
authors: Won-Kyung
authors: WK
authors: Ho
authors: Seong-Tae
authors: ST
authors: Kim
authors: Hana
authors: H
authors: Cho
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D006352:Heart Ventricles / Q000166:cytology*; D015640:Ion Channel Gating / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D015222:Sodium Channels / Q000378:metabolism*
chemical_list: D047428:Protein Kinase Inhibitors; D015222:Sodium Channels; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2