Furosemide- and bumetanide-sensitive ion transport and volume control in primary astrocyte cultures from rat brain

K + and Cl − transport using 42K + and 36Cl − was studied in primary astrocyte cultures prepared from neonatal rat brains. A component of 42K + uptake was sensitive to both furosemide and bumetanide with maximum inhibition being obtained at 1 and 0.01 mM concentrations of the inhibitors, respectively. Furosemide and bumetanide also markedly inhibited uptake of 36Cl −. 42K + uptake in the presence of ouabain was also sensitive to the omission of medium Na + and Cl −. These results suggest the existence of a K + + Na + + Cl − cotransport system in astrocyte cultures which in many cells has been shown to be involved in volume regulation. We studied volume changes using uptake of [ 14C]3-O-methyl- d-glucose ([ 14C]3-OMG), and also ion transport, in attached cells in response to exposure to hyper- or hypotonic medium. Exposure to medium made hypertonic with mannitol resulted in shrinkage of the [ 14C]3-OMG space of the cells, but did not affect 36Cl − content, expressed as nmol/mg protein. Exposure to hypotonic medium led to a marked increase in the [ 14C]3-OMG space, rapidly followed by a decrease towards control values. After the cells were then exposed to isotonic medium there was an immediate decrease followed by a slower increase in the [ 14C]3-OMG space. The increase in the [ 14C]3-OMG space was partially inhibited by 1 mM furosemide. These responses are similar to what has been described in a number of other cell types under the same conditions and show that astrocytes in primary culture show regulatory volume decrease after exposure to hypotonic medium and regulatory volume increase after subsequent exposure to isotonic medium which involves, in part, cation + Cl − cotransport. In contrast, the response of these cells to exposure to hypertonic medium seems to involve only osmotic shrinkage.