Intracellular pH rises and astrocytes swell after portacaval anastomosis in rats

The basis for astrocytic swelling after the early period after portacaval anastomosis (PCA) is poorly defined. In other eukaryotic cells intracellular pH (pHi) and volume are determined, in part, by the same general mechanisms, yet how astrocytic pHi varies with enlargement of these cells after PCA is unknown. Therefore, direct measurements of pHi in astrocytes were made and compared with pericapillary astrocytic area as determined from electron micrographs in rats 5-8 days after PCA. Astrocytic area (n = 14 measurements for each group) was found to be significantly (P less than 0.0009) greater in PCA animals (n = 3) than in sham-operated control animals. (n = 3). Double-barrel pH-sensitive microelectrodes were used to measure pHi in neocortical cells defined by electrophysiological criteria to be astrocytic. Astrocytes (n = 25) from PCA animals (n = 5) had a resting membrane potential of 72 +/- 5 mV (mean +/- SD) and an pHi of 7.11 +/- 0.11 while comparable cells (n = 12) from sham-operated controls (n = 2) had a membrane potential of 81 +/- 6 mV and an pHi of 7.00 +/- 0.10. Astrocytes from PCA animals were significantly more depolarized (P less than 0.001) and alkaline (P less than 0.009), at a time when they were also significantly larger than those from sham-operated controls. Astrocytes are known to become more alkaline when they are activated by brief depolarizing stimuli. However, this is the first demonstration that such an interrelationship can also exist for steady-state conditions of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)