title: CaMKII and at least two unidentified kinases phosphorylate regulatory light chain in non-contracting cardiomyocytes.
abstract: In cardiac tissue, regulatory light chain (RLC, myosin light chain 2) phosphorylation (Ser(15)) leads to modulation of muscle contraction through Ca(2+)-sensitization. To elucidate which kinases that are involved in the basal (diastolic phase) RLC phosphorylation, we studied non-contracting adult rat cardiomyocytes. RLC kinase activities in situ were unmasked by maximally inhibiting myosin light chain phosphatase (MLCP) by calyculin A in the absence and presence of various protein kinase inhibitors. Surprisingly MLCK did not contribute to the phosphorylation of RLC in the non-contracting cardiomyocytes. Two kinase activity groups were revealed by different sensitivities to staurosporine. The fraction with the highest sensitivity to staurosporine was inhibited by KN-93, a selective CaMKII inhibitor, producing a 23% ± 7% reduction in RLC phosphorylation. Calmodulin antagonism (W7) and reduction in Ca(2+) (EGTA) combined with low concentration of staurosporine caused a larger decrease in RLC phosphorylation than staurosporine alone. These data strongly suggest that in addition to CaMKII, there is another Ca(2+)/calmodulin-dependent kinase and a Ca(2+)/calmodulin-independent kinase phosphorylating RLC. Thus the RLC phosphorylation seems to be ensured by redundant kinase activities.
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway. Electronic address: hilde.eikemo@ntnu.no.
authors.forename: Hilde
authors.initials: H
authors.lastname: Eikemo
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway. Electronic address: l.r.moltzau@medisin.uio.no.
authors.forename: Lise Román
authors.initials: LR
authors.lastname: Moltzau
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway.
authors.forename: Cam H T
authors.initials: CHT
authors.lastname: Nguyen
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway. Electronic address: f.o.levy@medisin.uio.no.
authors.forename: Finn Olav
authors.initials: FO
authors.lastname: Levy
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway. Electronic address: tor.skomedal@medisin.uio.no.
authors.forename: Tor
authors.initials: T
authors.lastname: Skomedal
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway. Electronic address: j.b.osnes@medisin.uio.no.
authors.forename: Jan-Bjørn
authors.initials: JB
authors.lastname: Osnes
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D008297:Male; D032383:Myocytes, Cardiac / Q000201:enzymology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002147:Calmodulin; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium
keywords: Ca(2+)/calmodulin-dependent kinase II; Myosin light chain kinase; Myosin light chain phosphatase; Phosphorylation; Regulatory light chain (RLC, myosin light chain 2)