Preparation of an insoluble fraction of ox brain and its affinity for Na+ and K+.

A water insoluble fraction was prepared from ox cerebrum by homogenization in water, dialysis against water, washing with water and drying in air at 293 degrees K. The fraction represented 15.5 +/- 3% (n = 8) of the weight of the fresh brain; it contained means of 81% (n = 6) of the lipid, found in freshly dried ox brain samples, and 46% (n = 5) (biuret method) or 51% (n = 3) (6) of the protein, respectively. The Na+ and K+ concentrations were measured by atomic emission flame photometry, firstly, in prepared media, and then after 4 ml of the same media had been mixed with 1 g of the insoluble fraction at 310 degrees K for 20 min; the concentration in the fraction was calculated from that found in the medium. The concentration in the medium (mM) after incubation was compared with that calculated to be in the fraction, (mumol/g). When the insoluble fraction was mixed with Krebs Ringer saline containing bicarbonate and glucose, modified so that the ratios of NaCl and KCl varied-(although together they always added up to 150 mM)-there was a mean of 2.6 times as much Na+ or K+ in the fraction (mumol/g) as in the media (mM) when the latter contained up to 80 mM Na+ or K+. When the concentration of the cations in the media exceeded this value, the concentration of Na+ in the fraction rose considerably, while the concentration of K+ fell to zero. When only Ca2+ or only Mg2+ was omitted from the Krebs-Ringer bicarbonate glucose saline, the fraction did not take up Na+ or K+ from the medium at any concentration. On electron microscopy the fraction was granular and amorphous and contained myelin figures. The fraction did not take up any significant volume of oxygen measured manometrically either in the modified Krebs-Ringer solutions or in a mitochondrial substrate.