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.