Burn trauma and tumor necrosis factor alpha alter calcium handling by cardiomyocytes

It is well recognized that burn trauma induces an inflammatory cascade and the release of cytokines including tumor necrosis factor (TNF)-alpha. The negative inotropic effects of TNF-alpha on the heart are well recognized, but the cellular mechanisms remain unclear. To examine one aspect of cellular function, we exposed cardiac myocytes isolated from NZW rabbits (collagenase digestion) to either TNF-alpha (200, 400, or 1000 U/mL) or sham or burn plasma (10% by volume) for 3 to 4 h and measured calcium transient ratios in the isolated, contracting myocytes using the fluorescent indicator Fura-2-acetoxymethyl (1.2 microM); myocytes treated with media alone served as controls. Cells were placed in a perfusion chamber on the stage of an inverted Nikon microscope and superfused with buffer at 37 degrees C and stimulated at 1 Hz. A Tracor Northern Fluoroplex 1000 microspectrofluorometer and camera system, set to provide excitation of 340 and 380 nm with emission at 450-580 nm, was used to measure Ca2+ transients during systole-diastole. [Ca2+]i was reported as a fluorescence ratio (F340/F380) to minimize effects of different cell thickness and motion artifacts. After recording diastolic/systolic [Ca2+]i, cells were stimulated with isoproterenol, and [Ca2+]i was again measured. TNF-alpha produced diastolic and systolic [Ca2+]i values (1.067 +/- .023/1.301 +/- .017) that were similar to values seen after myocyte exposure to burn plasma (1.099 +/- .024/1.307 +/- .028) and significantly greater than values measured in controls (.857 +/- .017/1.077 +/- .015, p < .05). Our data confirm that burn trauma and TNF-alpha alter calcium handling by cardiomyocytes. The possible contribution of altered intracellular calcium dynamics to cardiac contractile abnormalities after burn trauma and TNF-alpha administration warrants further study.