Phosphorus nuclear magnetic resonance studies on the calcium-dependent energy metabolism of rat cerebrum under conditions of increased potassium in vitro.
Using phosphorus nuclear magnetic resonance (31P NMR) we studied the biochemical changes that accompany high-K+ depolarization in cerebral tissue in vitro. Rat brain slices (wet weight 4-6 g) were placed in a glass NMR sample tube which was superfused with well-oxygenated Krebs solution at 25 degrees C. The broad signal seen in the spectrum of brain slices almost disappeared after phospholipids were extracted by using chloroform and methanol. Phospholipids in the extracts were identified as phosphatidylcholine and phosphatidylethanolamine. In high-K+ Krebs solution tissue phosphocreatine (PCr) was decreased while inorganic phosphate (Pi) was increased, and in normal solution PCr and Pi recovered to control levels within about 20 min. The extent of changes in PCr and Pi depended on the concentrations of K+. Ouabain or tetrodotoxin did not influence these changes significantly. In calcium-free solution, where Ca2+ was replaced by Mg2+, the changes caused by high K+ were decreased to 40% of that in normal high-K+ solution. When ouabain was further added to the calcium-free solution, the changes were decreased to 10%. This suggested that the increased metabolism in high K+ was caused mainly by calcium-dependent mechanisms and partly by the Na(+)-K+ pump.