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Notes: 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 Km 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.

Notes: Abstract— The swelling of intact, exposed primate cerebral cortex perfused in vioo under, isosmotic conditions was a linear function of the concentration of K+ in perfusate over the range 25–117 mM. The K+-dependent swelling was manifested throughout the depth of the cerebral cortex studied and was associated with an increased content of chloride in the swollen tissue, despite the constancy of the concentration of external chloride. The swelling of the cerebral cortex was a linear function of the temperature of the perfusate over the range 15–38°C, despite the constancy of the concentration of external K+. Moreover, the content of chloride in the swollen cerebral cortex was a linear function of the temperature of the overlying perfusate, despite the constancy of the external concentration of chloride. The changes in the contents of Na+ and K+ in the swollen cerebral cortex perfused with solutions containing constant concentrations of external Na+ and K+ but differing in temperature suggested that the fluid of swelling in the tissue was rich in both K+ and CI-, as had been shown previously in vitro. Perfusion of the exposed, intact cerebral cortex in uiuo with K+-rich fluids usually involved the reciprocal reduction of the concentrations of Na+ in the perfusate to maintain isotonicity. When comparable reductions in the concentration of external Na+ were achieved by replacement with choline (instead of K+), swelling of the perfused, exposed cortex was significantly less than that attributed to isotonic, K+-rich but Na+-poor fluids. These observations suggested that it was the elevated levels of K+ rather than lowered concentrations of Na+ that promoted the swelling of the perfused cerebral cortex.The apparent rate of influx of 36Cl from the perfusate into the underlying exposed and intact monkey cerebral cortex in vivo was a linear function of the concentration of K+ in perfusate over the range 25–117 mM and conformed to Michaelis-Menten kinetics when plotted according to Lineweaver and Burk. Moreover, the apparent influx of chloride from perfusate into swollen cerebral cortex was a linear function of the percentage swelling of cerebral cortex over the range 6–30 per cent. However, the apparent rate of influx of chloride from perfusate into unswollen cortex was not consistent with the linear correlation already described for swollen cerebral cortex. One reason for this discrepancy was the reduction in the size of the true (inulin) extracellular space associated with the K+-dependent swelling of cerebral cortex in vivo. The anatomical locus for this K+-dependent swelling of cerebral cortex was an expanded glial compartment, as demonstrated by electron-microscopy. The parenteral administration (50 mg/kg) or local perfusion (5 mM) of acetazolamide inhibited the K+-dependent swelling of cerebral cortex in vivo. Moreover, administration of acetazolamide inhibited the K+-dependent increase in content of C1- and the K+-dependent rate of influx of 36Cl into swollen cerebral cortex. We have discussed the possible enzymatic basis of these K+-dependent alterations in content of fluid and chloride and transport of chloride in mammalian cerebral cortex in viuo.

Notes: Abstract— In monkeys we measured the steady-state concentrations of Cl− in endogenous CSF, in artificial CSF (which had equilibrated with the underlying exposed surface of the cerebral cortex but was not in diffusion equilibrium with endogenous CSF), and in arterial plasma. The ratio of the distribution of Cl− in artificial CSF to that in plasma was consistent with a passive Donnan distribution, whereas that ratio describing Cl− levels in endogenous CSF in comparison to those in plasma clearly exceeded theratio required for a passive, Donnan−type of distribution for Cl−. The kinetic analysis of the efflux of Cl− from blood into endogenous CSF and into artificial CSF (perfused over the exposed surface of the cerebral cortex) indicated that the rate of efflux of Cl− into endogenous CSF which was continuous with ventricular fluid was inhibited by acetazolamide [in confirmation of a similar finding described previously by Maren and Broder (1970)], whereas the rate of efflux of chloride from blood into the artificial CSF perfusate was uninfluenced by pretreatment of animals with acetazolamide. We have discussed the site of mediated (active) transport of chloride from blood into CSF in light of these findings.

Notes: Summary 1. The swelling of intact primate cerebral cortex perfused under isosmotic conditionsin vivo, like swelling of slices of mammalian cerebral cortex incubatedin vitro, is a linear function of the concentration of K+ in the extracellular fluid over the range 20–120 mM. 2. The simultaneous presence of the Cl− ion is required for the development of K+-dependent swelling of cerebral cortex under various experimental conditionsin vivo andin vitro. 3. The maintenance of previously established K+-dependent swelling of cerebral cortex bothin vitro andin vivo requires the relative concentrations of both K+ and Cl− in the extracellular fluid to remain constant. A reduction in the concentration of either ion is associated with an absolute loss of fluid of swelling of cerebral cortex. 4. The content of Cl− in cerebral cortex is a function of the magnitude of K+-dependent swelling even though the concentration of Cl− in the extracellular fluid is maintained constant. 5. The mechanism of swelling in primate cerebral cortex following cerebral circulatory arrest is discussed in the light of the experimental findings, as a model of the type of brain injury encountered in massive clinical stroke.