Control of brain slice respiration by ( Na+ + K+)-activated adenosine triphosphatase and the effects of enzyme inhibitors

Abstract

The involvement of membrane ( Na + + K +)-ATPase (Mg 2+-dependent, ( Na + + K +)-activated ATP phosphohydrolase, E.C. 3.6.1.3) in the oxygen consumption of rat brain cortical slices was studied in order to determine whether ( Na + + K +)-ATPase activity in intact cells can be estimated from oxygen consumption. The stimulation of brain slice respiration with K + required the simultaneous presence of Na +. Ouabain, a specific inhibitor of ( Na + + K +)-ATPase, significantly inhibited the ( Na + + K +)-stimulation of respiration. These observations suggest that the ( Na + + K +)-stimulation of brain slice respiration is related to ADP production as a result of ( Na + + K +)-ATPase activity. However, ouabain also inhibited non-K +-stimulated respiration. Additionally, ouabain markedly reduced the stimulation of respiration by 2,4-dinitrophenol in a high ( Na + + K +)-medium. Thus, ouabain depresses brain slice respiration by reducing the availability of ADP through ( Na + + K +)-ATPase inhibition and acts additionally by increasing the intracellular Na + concentration. These studies indicate that the use of ouabain results in an over-estimation of the respiration related to ( Na + + K +)-ATPase activity. This fraction of the respiration can be estimated more precisely from the difference between slice respiration in high Na + and K + media and that in choline, K + media. Studies were performed with two ( Na + + K +)-ATPase inhibitors to determine whether administration of these agents to intact rats would produce changes in brain respiration and ( Na + + K +)-ATPase activity. The intraperitoneal injection of digitoxin in rats caused an inhibition of brain ( Na + + K +)-ATPase and related respiration, but chlorpromazine failed to alter either ( Na + + K +)-ATPase activity or related respiration.