Regional distribution of potassium and phosphorus in ischemic brain tissue of rats with X-ray fluorescence analysis

Focal cerebral ischemia was induced by occlusion of the left middle cerebral artery (MCAO) for 1 and 3 hours in 14 rats. Five sham-operated rats served as controls. Regional cerebral blood flow (rCBF) was assessed by 14C-iodoantipyrine radioluminography. The potassium and phosphorus contents in brain tissue were assessed using energy-dispersive X-ray fluorescence spectrometry. In the inner periphery within the ischemic tissue where rCBF was severely reduced to 6.61 +/- 0.95 ml/100 g/min 1 hour after MCAO, the potassium content decreased slightly to 12.82 +/- 0.15 mg/g. Potassium content decreased further to 10.61 +/- 0.24 mg/g over 3 hours after occlusion, similar to that in the ischemic core. In contrast, in the outer periphery where rCBF was moderately reduced, the potassium fell slightly to 12.78 +/- 0.46 mg/g 3 hours after MCAO. Tissue phosphorus content decreased to 8.28 +/- 0.24 mg/g only in the ischemic core. These findings demonstrate that potassium and phosphorus in brain tissue depend primarily on the extent, magnitude and duration of ischemia. Ion homeostasis of cell membranes may not be completely disturbed in the periphery around ischemic tissue for a short time after the onset of ischemia, even though blood flow is markedly reduced.