title: Calpain inhibition reduces amplitude and accelerates decay of the late sodium current in ventricular myocytes from dogs with chronic heart failure.
abstract: Calpain is an intracellular Ca²⁺-activated protease that is involved in numerous Ca²⁺ dependent regulation of protein function in many cell types. This paper tests a hypothesis that calpains are involved in Ca²⁺-dependent increase of the late sodium current (INaL) in failing heart. Chronic heart failure (HF) was induced in 2 dogs by multiple coronary artery embolization. Using a conventional patch-clamp technique, the whole-cell INaL was recorded in enzymatically isolated ventricular cardiomyocytes (VCMs) in which INaL was activated by the presence of a higher (1 μM) intracellular [Ca²⁺] in the patch pipette. Cell suspensions were exposed to a cell- permeant calpain inhibitor MDL-28170 for 1-2 h before INaL recordings. The numerical excitation-contraction coupling (ECC) model was used to evaluate electrophysiological effects of calpain inhibition in silico. MDL caused acceleration of INaL decay evaluated by the two-exponential fit (τ₁ = 42±3.0 ms τ₂ = 435±27 ms, n = 6, in MDL vs. τ₁ = 52±2.1 ms τ₂ = 605±26 control no vehicle, n = 11, and vs. τ₁ = 52±2.8 ms τ₂ = 583±37 ms n = 7, control with vehicle, P<0.05 ANOVA). MDL significantly reduced INaL density recorded at -30 mV (0.488±0.03, n = 12, in control no vehicle, 0.4502±0.0210, n = 9 in vehicle vs. 0.166±0.05pA/pF, n = 5, in MDL). Our measurements of current-voltage relationships demonstrated that the INaL density was decreased by MDL in a wide range of potentials, including that for the action potential plateau. At the same time the membrane potential dependency of the steady-state activation and inactivation remained unchanged in the MDL-treated VCMs. Our ECC model predicted that calpain inhibition greatly improves myocyte function by reducing the action potential duration and intracellular diastolic Ca²⁺ accumulation in the pulse train.
  
  
  CONCLUSIONS
  Calpain inhibition reverses INaL changes in failing dog ventricular cardiomyocytes in the presence of high intracellular Ca²⁺. Specifically it decreases INaL density and accelerates INaL kinetics resulting in improvement of myocyte electrical response and Ca²⁺ handling as predicted by our in silico simulations.
authors.affiliation: Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan, United States of America. adas7247@yahoo.com
authors.forename: Albertas
authors.initials: A
authors.lastname: Undrovinas
authors.forename: Victor A
authors.initials: VA
authors.lastname: Maltsev
authors.forename: Hani N
authors.initials: HN
authors.lastname: Sabbah
mesh_terms: D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors*; D003198:Computer Simulation; D004151:Dipeptides / Q000494:pharmacology; D004195:Disease Models, Animal; D004285:Dogs; D006333:Heart Failure / Q000201:enzymology* / Q000503:physiopathology*; D006352:Heart Ventricles / Q000201:enzymology* / Q000503:physiopathology*; D008564:Membrane Potentials; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D012964:Sodium / Q000378:metabolism
chemical_list: D004151:Dipeptides; D012964:Sodium; D002154:Calpain; C058076:calpain inhibitor III