We hypothesize that lung ischemic injury is related to cessation of flow leading to endothelial cell membrane depolarization and activation of
oxidant-generating systems. Cell membrane potential was assessed in isolated,
oxygen ventilated, Krebs-Ringer
bicarbonate buffer-
dextran-perfused rat lungs by lung surface fluorescence after infusion of
bis-oxonol or 5,5',6,6'-tetrachloro-1, 1',3,3'-tetraethylbenzimidazolyl-carbocyanine
iodide (JC-1), voltage-sensitive
dyes. Surface fluorometry showed increased
bis-oxonol fluorescence (34.7 +/- 3.3% above baseline) and decreased
JC-1 fluorescence (24.5 +/- 4.5% below baseline) with
ischemia, compatible with membrane depolarization. Fluorescence change was initiated within 1-2 min of the onset of
ischemia and was rapidly reversible with reperfusion. Fluorescence changes varied with perfusion flow rate; maximal increase occurred with the transition from 1.8 ml/min to zero flow. Elevation of static intravascular pressure resulted in only a minor increase of
bis-oxonol fluorescence. In situ subpleural fluorescence microscopy showed that endothelial cells are the major site of the increased
bis-oxonol fluorescence signal with
ischemia. These results indicate that endothelial cell membrane depolarization represents an early event with lung
ischemia. Since the
adenosine triphosphate content of lung was unchanged with
ischemia in the O2-ventilated lungs, we postulate that membrane depolarization results from elimination of shear stress, possibly via inactivation of flow-sensitive K+-channels.