SITS-inhibitable Cl- transport and Na+-dependent H+ production in primary astroglial cultures

The uptake and efflux of Cl- were measured in primary astroglial cultures from neonatal rat brain using 36Cl- as a tracer. Both uptake and efflux were found to be inhibited by the specific anion inhibitor SITS. The rate of Cl- efflux showed a broad optimum at pH values greater than 7.5, and both this pH dependence and the effect of SITS suggests that these cells contain a Cl- in equilibrium Cl- or Cl- in equilibrium HCO3- exchange carrier similar to that described in erythrocytes. In addition, the cells rapidly lost Cl- when placed in media of decreasing Cl- concentrations, and ploting the initial rate of uptake of 36Cl- as a function of external Cl- concen-ration gave an apparent Km for Cl- uptake of 56 mM. Pretreatment of these cultures with DBcAMP is known to cause the cells to form numerous processes, resulting in their morphology more closely resembling that of astroglia in brain. Treatment with DBcAMP resulted in decreased equilibrium levels of 36Cl- and a small decrease in the initial rate of uptake of 36Cl-, but did not affect inhibition by SITS. Addition of Na+ to the cells suspended in Na+-free media specifically increased the rate of acidification of the medium. These observations suggest that these cells have both Cl- in equilibrium HCO3- and Na+ in equilibrium H+ exchange processes which, if these cultures can be considered to be representative of cells in vivo, may also occur in astroglial cells in the central nervous system. Based on these results and other work, a model is proposed by which these processes would lead to the astroglial swelling which is often observed in vivo in pathological conditions.