Properties and localization of bicarbonate-stimulated ATPase activity in rat brain

Abstract— A 20–30 per cent stimulation of ATPase activity by added NaHCO₃ was found in homogenates of a variety of mammalian tissues. The subcellular distribution of this (HCO₃^-)—stimulated activity was examined in detail using rat cerebral cortex. The stimulation was specific for the HCO₃^- ion and was predominantly localized in the mitochondrial subcellular fraction, in which a 2-fold stimulation by HCO₃^- was found. The effect of inhibitors supported the identification as the mitochondrial ATPase. Both sodium azide and thiocyanate were inhibitory. The effects of varying the Mg²⁺ concentration, HCO₃^- concentration, and pH were also studied. In the presence of HCO₃^- the K_m for ATP was reduced approximately 3-fold. There was no effect of HCO₃^- on the ma + K) ATPase or Mg²⁺ ATPase from the microsomal fraction of rat cerebral cortex. Our findings have been discussed in relation to previous work on HCO₃^- stimulation of ATPae activity in subcellular fractions from other tissues, as well as its possible relevance to the known effects of HCO₃^- and carbonic anhydrase on active ion transport.