title: CaMKII inhibition targeted to the sarcoplasmic reticulum inhibits frequency-dependent acceleration of relaxation and Ca2+ current facilitation.
abstract: Cardiac Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in heart has been implicated in Ca(2+) current (I(Ca)) facilitation, enhanced sarcoplasmic reticulum (SR) Ca(2+) release and frequency-dependent acceleration of relaxation (FDAR) via enhanced SR Ca(2+) uptake. However, questions remain about how CaMKII may work in these three processes. Here we tested the role of CaMKII in these processes using transgenic mice (SR-AIP) that express four concatenated repeats of the CaMKII inhibitory peptide AIP selectively in the SR membrane. Wild type mice (WT) and mice expressing AIP exclusively in the nucleus (NLS-AIP) served as controls. Increasing stimulation frequency produced typical FDAR in WT and NLS-AIP, but FDAR was markedly inhibited in SR-AIP. Quantitative analysis of cytosolic Ca(2+) removal during [Ca(2+)](i) decline revealed that FDAR is due to an increased apparent V(max) of SERCA. CaMKII-dependent RyR phosphorylation at Ser2815 and SR Ca(2+) leak was both decreased in SR-AIP vs. WT. This decrease in SR Ca(2+) leak may partly balance the reduced SERCA activity leading to relatively unaltered SR-Ca(2+) load in SR-AIP vs. WT myocytes. Surprisingly, CaMKII regulation of the L-type Ca(2+) channel (I(Ca) facilitation and recovery from inactivation) was abolished by the SR-targeted CaMKII inhibition in SR-AIP mice. Inhibition of CaMKII effects on I(Ca) and RyR function by the SR-localized AIP places physical constraints on the localization of these proteins at the junctional microdomain. Thus SR-targeted CaMKII inhibition can directly inhibit the activation of SR Ca(2+) uptake, SR Ca(2+) release and I(Ca) by CaMKII, effects which have all been implicated in triggered arrhythmias.
authors.affiliation: Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL 60153, USA.
authors.forename: Eckard
authors.initials: E
authors.lastname: Picht
authors.forename: Jaime
authors.initials: J
authors.lastname: DeSantiago
authors.forename: Sabine
authors.initials: S
authors.lastname: Huke
authors.forename: Marcia A
authors.initials: MA
authors.lastname: Kaetzel
authors.forename: John R
authors.initials: JR
authors.lastname: Dedman
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: C503464:CaMKII inhibitor AIP; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases