Carbonic acid buffer changes during complete brain ischemia.
Simultaneous measurements of tissue PCO2 (PtCO2), interstitial H+ concentration ([H+]o), and tissue lactate content were used to examine changes in interstitial HCO3- concentration ([HCO3-]o) during complete ischemia. In normoglycemic rats (blood glucose of 6-8 mM; neocortical ischemic-induced lactate content 8-12 mmol/kg) [H+]o increased from 7.22 +/- 0.02 to 6.79 +/- 0.02 pH (n = 3). By contrast, in hyperglycemic rats (blood glucose 18-75 mM; ischemic-induced lactate content 19-31 mmol/kg) [H+]o rose by a significantly larger amount to 6.19 +/- 0.02 pH (n = 7). Given that HCO3- is the predominant interstitial H+ buffer, changes in peak PtCO2 show why peak [H+]o were bimodally distributed compared with lactate content. Between 8 and 12 mmol/kg lactate, when peak PtCO2 rose from 99 to 186 Torr but [H+]o was constant at 6.79 pH, calculated [HCO3-]o increased from 11.9 to 21.9 mM. Then after transitional changes, peak PtCO2 and [H+]o remained constant at 389 +/- 9 Torr (n = 7) and 6.19 pH despite the fact that tissue lactate ranged from 19 to 31 mmol/kg lactate, respectively; [HCO3-]o must have remained constant at 12.3 +/- 0.7 mM (n = 7). Since ischemic brain continued to produce another 12 more mmol/kg of lactic acid above 19 mmol/kg lactate without further changes in PtCO2 or [H+]o, H+ and HCO3- must have been heterogeneously compartmented. The continued lactic acid production occurred in a compartment that occupied 36% of neocortical space. This compartment is likely to represent glial cells.
Kraig
R P
RP
Pulsinelli
W A
WA
Plum
F
F
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002545:Brain Ischemia / Q000378:metabolism*; D002021:Buffers; D002245:Carbon Dioxide / Q000378:metabolism; D002254:Carbonates / Q000378:metabolism*; D002255:Carbonic Acid / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D007773:Lactates / Q000096:biosynthesis; D008297:Male; D008954:Models, Biological; D009994:Osmolar Concentration; D010313:Partial Pressure; D051381:Rats; D011919:Rats, Inbred Strains
D001639:Bicarbonates; D002021:Buffers; D002254:Carbonates; D007773:Lactates; D002245:Carbon Dioxide; D002255:Carbonic Acid; D006859:Hydrogen