RELATIONSHIP BETWEEN INTRACELLULAR AND EXTRACELLULAR PH IN PRIMARY CULTURES OF RAT ASTROCYTES

We studied the influence of extracellular pH (pH(e)) on the mechanisms regulating intracellular pH (pH(i)) in astrocytes cultured from neona tal rat cortex, using single cell microspectrofluorometry and the pH-s ensitive fluorophore 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein . When pH(e) was maintained at control values of 7.35 during acid tran sients caused by an increased CO2 tension, pH(i) was rapidly regulated back to normal. However, at pH(e) 6.9 or below, there was no recovery of pH(i). Steady-state pH(i) was also strongly dependent on pH(e) (pH (i) = 1.14 + 0.80 pH(e)). The pH(i) recovery after normalization of pH (e) was very rapid, indicating that a prolonged exposure to a low pH s timulates pH-regulating mechanisms, and was inhibited by 4,4'-diisothi ocyanostilbene-2,2'-disulfonic acid (DIDS) and amiloride or the remova l of Na+. Recovery was also slowed down by Cd2+. The pH(e)-dependent a cidification was not critically influenced by DIDS or amiloride and wa s not inhibited by tetrodotoxin, tetraethylammonium, ihydroxy-6-nitro- 7-sulfamoyl-benzo(F)-quinoxaline, kynurenic acid, 5-hydroxysaclofen, b icuculline, Cd2+, or albumin. The results emphasize the importance of pH(e) for pH(i) regulation and suggest that in astrocytes pH(i) is not regulated back to normal levels until pH(e) is normalized.