Anion transport in astrocytes.

We have examined the question of anion-transport systems in glia using primary astrocyte cultures prepared from neonatal rat brains. These studies show that these cells have exchange or cotransport systems for Cl- that appear to be electrically neutral, that is, SITS-sensitive Cl-/Cl- or Cl-/HCO3- anion exchange, and furosemide- and bumetanide-sensitive Na+ + K+ + 2Cl- cotransport. These inhibitors inhibit a major component of the total 36Cl- flux and the remaining Cl- flux may be conductive; however, this conductive flux makes a small contribution to Em relative to K+, since large changes in [Cl-]o do not usually affect Em, which is predominantly a K+ diffusion potential. We have also found an alpha-receptor-mediated depolarization that is affected by imposed changes in Ecl. The alpha-receptor-mediated depolarization seen at normal [Cl-]o could be partially due to increased Cl- conductance because [Cl-]i appears to be several-fold higher than it would be if it were in equilibrium with the membrane potential.