title: Regulation of intracellular pH in reticulospinal neurones of the lamprey, Petromyzon marinus.
abstract: 1. The regulation of intracellular pH (pHi) in lamprey reticulospinal neurones was investigated with pH-sensitive micro-electrodes based on a neutral carrier liquid membrane. Experiments were performed using an in vitro brain-stem preparation. 2. In HEPES-buffered solutions, extracellular pH (pHo) was consistently more acidic than the pH of the bathing solution (pHb). In HCO3(-)-buffered solutions, the brain was also relatively acidic, but the brain pH gradient was smaller. 3. In HEPES- and HCO3(-)-buffered solutions, mean pHi was 7.40-7.50. This range was too high to be explained by a passive distribution of H+, OH- or HCO3-. 4. In nominally HCO3(-)-free, HEPES-buffered solution, cells were acid loaded by addition and subsequent withdrawal of NH4+ from the superfusate. pHi recovered from acid loading by an energy-dependent process in 10-20 min. Recovery from acid loading in HEPES-buffered solutions was blocked by exposure to amiloride. 5. Removal of extracellular Na+ caused a slow, accelerating fall of pHi. Return of Na+ to the bath caused an immediate reversal of this acidification, followed by a slow recovery of pHi. Measurement with Na+-sensitive micro-electrodes during acid loading showed a rapid rise in the intracellular Na+ activity [( Na+]i). 6. Following acid loading, transition from HEPES- to HCO3(-)-buffered solutions caused an increase in the acid extrusion rate of at least 48%. The effect of these solution changes was dependent on pHo. After blocking pHi recovery with amiloride, transition from HEPES- to HCO3(-)-buffered Ringer plus amiloride produced a slow recovery of pHi. 7. Recovery from acid loading in HCO3(-)-buffered solutions was inhibited 65% by the anion transport blocker DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid). Recovery from acid loading after incubation in Cl(-)-free solution was slower than recovery after replenishment of Cl-. 8. It is concluded that in HCO3(-)-free solutions, pHi regulation is accomplished by a Na-H exchange mechanism. In the presence of extracellular HCO3- an additional mechanism can operate to extrude intracellular acid.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001921:Brain / Q000502:physiology*; D002712:Chlorides / Q000494:pharmacology; D005399:Fishes / Q000502:physiology*; D006531:HEPES / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007798:Lampreys / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D000091402:Prohibitins; D012964:Sodium / Q000494:pharmacology; D013116:Spinal Cord / Q000502:physiology*
chemical_list: D001639:Bicarbonates; D002712:Chlorides; C000717328:PHB protein, human; D000091402:Prohibitins; D000643:Ammonium Chloride; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D006531:HEPES