title: Modulation of late sodium current by Ca2+, calmodulin, and CaMKII in normal and failing dog cardiomyocytes: similarities and differences.
abstract: Augmented and slowed late Na(+) current (I(NaL)) is implicated in action potential duration variability, early afterdepolarizations, and abnormal Ca(2+) handling in human and canine failing myocardium. Our objective was to study I(NaL) modulation by cytosolic Ca(2+) concentration ([Ca(2+)](i)) in normal and failing ventricular myocytes. Chronic heart failure was produced in 10 dogs by multiple sequential coronary artery microembolizations; 6 normal dogs served as a control. I(NaL) fine structure was measured by whole cell patch clamp in ventricular myocytes and approximated by a sum of fast and slow exponentials produced by burst and late scattered modes of Na(+) channel gating, respectively. I(NaL) greatly enhanced as [Ca(2+)](i) increased from "Ca(2+) free" to 1 microM: its maximum density increased, decay of both exponentials slowed, and the steady-state inactivation (SSI) curve shifted toward more positive potentials. Testing the inhibition of CaMKII and CaM revealed similarities and differences of I(NaL) modulation in failing vs. normal myocytes. Similarities include the following: 1) CaMKII slows I(NaL) decay and decreases the amplitude of fast exponentials, and 2) Ca(2+) shifts SSI rightward. Differences include the following: 1) slowing of I(NaL) by CaMKII is greater, 2) CaM shifts SSI leftward, and 3) Ca(2+) increases the amplitude of slow exponentials. We conclude that Ca(2+)/CaM/CaMKII signaling increases I(NaL) and Na(+) influx in both normal and failing myocytes by slowing inactivation kinetics and shifting SSI. This Na(+) influx provides a novel Ca(2+) positive feedback mechanism (via Na(+)/Ca(2+) exchanger), enhancing contractions at higher beating rates but worsening cardiomyocyte contractile and electrical performance in conditions of poor Ca(2+) handling in heart failure.
authors.affiliation: Henry Ford Hosp., Cardiovascular Research, Education & Research, Detroit, MI 48202-2689, USA.
authors.forename: Victor A
authors.initials: VA
authors.lastname: Maltsev
authors.forename: Vitaliy
authors.initials: V
authors.lastname: Reznikov
authors.forename: Nidas A
authors.initials: NA
authors.lastname: Undrovinas
authors.forename: Hani N
authors.initials: HN
authors.lastname: Sabbah
authors.forename: Albertas
authors.initials: A
authors.lastname: Undrovinas
mesh_terms: D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000378:metabolism; D001596:Benzylamines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002908:Chronic Disease; D003600:Cytosol / Q000378:metabolism; D004195:Disease Models, Animal; D004285:Dogs; D006333:Heart Failure / Q000150:complications / Q000201:enzymology / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism; D015640:Ion Channel Gating; D007700:Kinetics; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012107:Research Design; D015398:Signal Transduction / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D000096926:Benzenesulfonamides
chemical_list: D001596:Benzylamines; D002118:Calcium; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002147:Calmodulin; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D012964:Sodium; D015222:Sodium Channels; D013449:Sulfonamides; C072105:KN 93; D000096926:Benzenesulfonamides