The dependence of the respiration of brain cortex on active cation transport

Abstract

An attempt was made to determine whether the energy-requiring uptake of K+ ions acts as a pace-maker for respiration in slices of rabbit-brain cortex. Respiration of both slices and homogenates was measured under conditions of incubation such that the active transport was inhibited without the use of respiratory poisons. Uptake and the retention of K by slices during incubation in a saline medium containing glucose was inhibited by low concentrations of the glycoside ouabain, about 0. 5 [mu]m being required to produce half-maximal inhibition. With maximum inhibition, the K concentration of the tissue was only 30% of that in the control. Ouabain also caused about a 40% fall in the Qo2 of slices under conditions when K transport was inhibited. The same results were obtained when the medium contained glucose plus glutamate. Incubation of slices in a medium in which sodium had been replaced with choline caused falls in the K concentration and in the Q02, each of which was not further decreased by the addition of ouabain. Respiration of homogenates was also depressed by the addition of ouabain (5 um) in a high-Na medium and by the replacement of the medium Na with K, choline or sucrose; under the last-named conditions, as was found with slices, no further fall occurred with ouabain. About 40% of the respiration and the active uptake of potassium by brain cortex are inhibited by ouabain and by deprivation of the medium of sodium. The inhibition by ouabain of both K transport and respiration was manifest only in the presence of Na in the medium. A cell component connected with the process of active transport and equally sensitive to inhibition by ouabain and to activation by Na therefore appears to be capable of controlling about 40% of the tissue''s respiration.