Calpain inhibition reduces amplitude and accelerates decay of the late sodium current in ventricular myocytes from dogs with chronic heart failure.

Abstract

UNLABELLED: Calpain is an intracellular Ca&#xb2;&#x207a;-activated protease that is involved in numerous Ca&#xb2;&#x207a; dependent regulation of protein function in many cell types. This paper tests a hypothesis that calpains are involved in Ca&#xb2;&#x207a;-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 &#x3bc;M) intracellular [Ca&#xb2;&#x207a;] 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 (&#x3c4;&#x2081;&#x200a;=&#x200a;42&#xb1;3.0 ms &#x3c4;&#x2082;&#x200a;=&#x200a;435&#xb1;27 ms, n&#x200a;=&#x200a;6, in MDL vs. &#x3c4;&#x2081;&#x200a;=&#x200a;52&#xb1;2.1 ms &#x3c4;&#x2082;&#x200a;=&#x200a;605&#xb1;26 control no vehicle, n&#x200a;=&#x200a;11, and vs. &#x3c4;&#x2081;&#x200a;=&#x200a;52&#xb1;2.8 ms &#x3c4;&#x2082;&#x200a;=&#x200a;583&#xb1;37 ms n&#x200a;=&#x200a;7, control with vehicle, P<0.05 ANOVA). MDL significantly reduced INaL density recorded at -30 mV (0.488&#xb1;0.03, n&#x200a;=&#x200a;12, in control no vehicle, 0.4502&#xb1;0.0210, n&#x200a;=&#x200a;9 in vehicle vs. 0.166&#xb1;0.05pA/pF, n&#x200a;=&#x200a;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 Ca&#xb2;&#x207a; accumulation in the pulse train. CONCLUSIONS: Calpain inhibition reverses INaL changes in failing dog ventricular cardiomyocytes in the presence of high intracellular Ca&#xb2;&#x207a;. Specifically it decreases INaL density and accelerates INaL kinetics resulting in improvement of myocyte electrical response and Ca&#xb2;&#x207a; handling as predicted by our in silico simulations.