Cl-HCO3 exchange in choroid plexus: analysis by the DMO method for cell pH.
[14C]DMO distribution was used to measure steady-state intracellular pH (pHi) and [HCO3]i in adult rat choroid plexus (CP) incubated in synthetic cerebrospinal fluid (CSF) for 30 min. In controls at 37 degrees C, mean pHi (6.95 at PCO2 = 30 mmHg) was close to corresponding in vivo values; and [HCO3]i/[HCO3]csf, i.e., rHCO3, was 0.37. At normal [HCO3]csf = 18 mM, cell HCO3 was accumulated threefold above electrochemical equilibrium (as estimated from Em = -50 mV). [HCO3]i decreased proportionally with [HCO3]csf, as the latter was altered from 47 to 9 mM; in severe extracellular acidosis [( HCO3]csf = 3.7 mM), [HCO3]i was not reduced further and so rHCO3 rose to 0.66. Except in low [HCO3]csf, acetazolamide and ouabain (10(-4) M) caused small depletion of cell HCO3. 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid lowered [HCO3]i by 60%, thus decreasing rHCO3 (0.16) and rCl (0.25) to values close to estimated equilibrium distribution (0.15). Substitution of CSF Cl with isethionate resulted in marked alkalinization of pHi when [Cl]csf was depleted to 12 mM. Augmented PCO2 associated with temperature reduction to 15 degrees C elevated [HCO3]i, thereby increasing rHCO3 (to 0.66) as well as rCl. Anion distribution ratios indicate heteroanion exchange in mammalian CP.
Johanson
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Parandoosh
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Smith
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D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002555:Cerebrospinal Fluid / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D002831:Choroid Plexus / Q000187:drug effects / Q000378:metabolism*; D004114:Dimethadione; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007444:Inulin; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature
D001639:Bicarbonates; D002250:Carbon Radioisotopes; D002712:Chlorides; D007473:Ion Channels; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D010042:Ouabain; D007444:Inulin; D004114:Dimethadione; D000086:Acetazolamide