Myocyte contractility with caspase inhibition and simulated hyperkalemic cardioplegic arrest.
BACKGROUND
Exposure of left ventricular (LV) myocytes to simulated hyperkalemic cardioplegic arrest (HCA) has been demonstrated to perturb ionic homeostasis and adversely affect myocyte contractility on rewarming. Altered ionic homeostasis can cause cytosolic activation of the caspases. While caspases participate in apoptosis, these proteases can degrade myocyte contractile proteins, and thereby alter myocyte contractility. Accordingly, this study tested the hypothesis that caspase inhibition during HCA would attenuate the degree of myocyte contractile dysfunction upon rewarming, independent of a loss in myocyte viability.


METHODS
Porcine (n = 8) LV myocytes were isolated and assigned to the following treatment groups: normothermic control: incubation in cell culture media for 2 hours at 37 degrees C; HCA only: incubation for 2 hours in hypothermic HCA solution (4 degrees C, 24 mEq K(+)); or incubation in hypothermic HCA solution supplemented with 10 microM of the caspase inhibitor, z-VAD (z-Val-Ala-Asp-fluoromethyl-ketone, HCA+zVAD). Myocyte viability, assayed as a function of mitochondrial function, was determined to be similar in the normothermic and both HCA groups.


RESULTS
The HCA caused a significant reduction in myocyte shortening velocity compared with normothermic control values (41 +/- 6 versus 86 +/- 8 microm/s, p < 0.05). The HCA+zVAD group had significantly improved myocyte shortening velocity compared with the HCA only group (63 +/- 7 microm/s, p < 0.05).


CONCLUSIONS
Independent of changes in viability, caspase inhibition attenuated myocyte contractile dysfunction after HCA and rewarming. Thus, caspase activation during HCA contributes, at least in part, to impaired myocyte contractility with rewarming. Supplementation of HCA with caspase inhibitors may provide a means to preserve myocyte contractile function after cardioplegic arrest.
Mukherjee
Rupak
R
Division of Cardiothoracic Surgery Research, Medical University of South Carolina, Charleston, South Carolina 29425, USA. mukherr@musc.edu
Yarbrough
William M
WM
Reese
Emily S
ES
Leiser
Jennifer S
JS
Sample
Jeffrey A
JA
Mingoia
Joseph T
JT
Hardin
Amy E
AE
Stroud
Robert E
RE
McLean
Julie E
JE
Hendrick
Jennifer W
JW
Spinale
Francis G
FG
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology*; D000818:Animals; D002314:Cardioplegic Solutions; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology; D002470:Cell Survival; D002478:Cells, Cultured; D006324:Heart Arrest, Induced / Q000379:methods; D006801:Humans; D006947:Hyperkalemia / Q000503:physiopathology; D007036:Hypothermia, Induced; D007552:Isotonic Solutions; D032342:Muscle Cells / Q000187:drug effects / Q000502:physiology*; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D011897:Random Allocation; D017694:Rewarming; D000077331:Ringer's Solution; D013552:Swine
D000590:Amino Acid Chloromethyl Ketones; D002314:Cardioplegic Solutions; D061945:Caspase Inhibitors; D007552:Isotonic Solutions; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D000077331:Ringer's Solution; D020169:Caspases