V. Crepel et al., MITOGEN-ACTIVATED PROTEIN AND TYROSINE KINASES IN THE ACTIVATION OF ASTROCYTE VOLUME-ACTIVATED CHLORIDE CURRENT, The Journal of neuroscience, 18(4), 1998, pp. 1196-1206
Astrocytes swell during neuronal activity as they accumulate K+ to buf
fer the increase in external K+ released from neurons, This swelling a
ctivates volume-sensitive Cl- channels, which are thought to be import
ant in regulatory Volume decrease and in the response ct the CNS to tr
auma and excitotoxicity. Mitogen-activated protein (MAP) kinases also
are activated by cell volume changes, but their roles in volume regula
tion are unknown, We have investigated the role of tyrosine and MAP ki
nases in the activation of volume-activated Cl- channels in cultured a
strocytes, using whole-cell patch-clamp recording and Western immunobl
ot, As previously described, hypoosmotic solution induced an outwardly
rectifying Cl- current, which was blocked by NPPB and SITS. This Cl-
current did not depend on [Ca2+](i) because ii was still observed when
20 mM BAPTA was included in the pipette, but it did exhibit rundown w
hen ATP was omitted. Inhibition of tyrosine kinases with genistein or
tyrphostin A23 (but not the inactive agents daidzein and tyrphostin Al
) blocked the Cl- current. The MAP kinase kinase (MEK) inhibitor PD 98
059 reversibly inhibited activation of the Cl- current by hypo-osmotic
solution. Western immunoblots showed that genistein or PD 98059 block
ed activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocyte
s. Therefore, activation of tyrosine and MAP kinases by swelling is a
critical step in the opening of volume-sensitive Cl- channels.