H+ transport from CNS in hypercapnia and regulation of CSF [HCO3-].
CSF HCO3- increases more than plasma HCO3- in hypercapnia, and there are at least two sources for the CSF HCO3- increase--one derived from the simultaneous increase in plasma HCO3-, and the other, HCO3-formed from hydration of CO2 in the choroid plexus and glia and susceptible to inhibition by acetazolamide (J. Appl. Physiol. 38: 504-512, 1975). It was proposed that the H+ formed in the CNS in CO2 hydration is actively exchanged for plasma Na+ utilizing the Na-K ATPase pump. H+ transport from the CNS was therefore studied in four groups of dogs breathing 5% CO2 at constant VA for 4 h with repeated injections of saline, acetazolamide 5 mg/ml, ouabain 0.1 mg/ml, and acetazolamide and ouabain together into lateral cerebral ventricles. Arterial HCO3-increased 2.5 meq/l at 4 h of hypercapnia in all groups. CSF HCO3-increased 5.8 meq/l in the saline-injected animals, but it increased only about 2 meq/l and equaled plasma HCO3- rise in the other three groups. Therefore CNS HCO3- formation in hypercapnia can be blocked by inhibiting the CO2 hydration reaction with acetazolamide or by blocking H+ removal by inhibiting Na-K ATPase with ouabain. The data support the thesis of active H+ removal from the CNS in exchange for plasma Na+ in hypercapnia.
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000097:blood / Q000134:cerebrospinal fluid*; D001692:Biological Transport; D002245:Carbon Dioxide / Q000097:blood / Q000134:cerebrospinal fluid; D002490:Central Nervous System / Q000378:metabolism*; D002831:Choroid Plexus / Q000378:metabolism; D004285:Dogs; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010100:Oxygen / Q000097:blood / Q000134:cerebrospinal fluid
D001639:Bicarbonates; D002245:Carbon Dioxide; D010042:Ouabain; D006859:Hydrogen; D000086:Acetazolamide; D010100:Oxygen