Development of an acute burn model in adult mice for studies of cardiac function and cardiomyocyte cellular function

The increasing availability of mice with gene supplementation (transgenic), site-specific inactivation mutations (gene "knock-outs"), or site-specific genetic modification mutations (gene "knock-ins") has spurred interest in the development of murine trauma models. In this study, C57 BL/6 mice (28 g ) were given a cutaneous burn over 40% total body surface area by applying brass probes (1 x 2 x 0.003 cm) heated to 100 degreesC in boiling water to the animals side and back for 5 s. Shams received anesthesia alone and not burn. Mice were killed 24 h post-burn to determine presence of partial-thic kness or full-thickness burn injury, cardiac contractile function (Langendo rff perfusion, n = 7 or 8 mice/group) or to examine cardiac myocyte cytokin e secretion in isolated cardiomyocytes (collagenase perfusion, n = 4 or 5 m ice/group). All mice were killed 24 h post-burn for subsequent cardiac or c ardiomyocyte studies. Our studies confirm that this murine model of burn tr auma produced mixed partial- or full-thickness burn injury, whereas there w as no necrosis or inflammation in sham burn mice. Baseline hematocrits were similar in all mice (44 +/- 1) but decreased after burn trauma (37 +/- 1), likely because of the volume of fluid resuscitation and hemodilution. Burn trauma impaired cardiac contraction and relaxation as indicated by the low er left ventricular pressure (LVP) measured in burn (56 4) compared to that measured in shams (84 +/- 1 mmHg, P < 0.001), a lower rate of LVP rise (+d P/dt max, 1393 +/- 10 vs. 2000 +/- 41 mmHg/s, P < 0.002), and reduced LVP f all (-dP/dt max, 1023 +/- 40 vs. 1550 +/- 50, P < 0.001). These differences occurred despite similar coronary perfusion pressures and heart rates in b oth sham and burn mice. Ventricular function curves were shifted downward i n the burn mice in the direction of contractile failure; in addition, heart s from burn mice had reduced LVP and +/- dP/dt responses to increases in co ronary flow rate, increases in perfusate Ca2+, and to isoproterenol challen ge (P < 0.05). Burn trauma promoted cardiac myocyte secretion of tumor necr osis factor (TNF alpha) (175 +/- 6 pg/mL) compared to that measured in sham s (72 +/- 9 pg/mL, P < 0.05); burn trauma also increased cardiac myocyte se cretion of interleukin 10 (IL-1 beta) (sham: 2 +/- 0.5; burn: 22 +/- 1 pg/m L, P < 0.05) and IL-6 (sham: 70 +/- 6; burn: 148 +/- 16 pg/mL, P < 0.05). A nti-TNF alpha strategies prevented burn-mediated cardiac contractile defici ts. Burn trauma altered Ca2+ homeostasis in murine cardlomyocytes (Fura-2 A M loading). [Ca (2+)](i) in myocytes from burns (185 +/- 4 nM) was higher t han values measured in myocytes from shams (86 +/- nM, P < 0.05). These dat a confirm that the murine burn model provides a reasonable approach to stud y the molecular and cell biology of inflammation in organ dysfunction after burn trauma.