Mitogen-Activated Protein and Tyrosine Kinases in the Activation of Astrocyte Volume-Activated Chloride Current

Abstract

Astrocytes swell during neuronal activity as they accumulate K+ to buffer the increase in external K+ released from neurons. This swelling activates volume-sensitive Cl- channels, which are thought to be important in regulatory volume decrease and in the response of the CNS to trauma and excitotoxicity. Mitogen-activated protein (MAP) kinases also are activated by cell volume changes, but their roles in volume regulation are unknown. We have investigated the role of tyrosine and MAP kinases in the activation of volume-activated Cl- channels in cultured astrocytes, using whole-cell patch-clamp recording and Western immunoblots. As previously described, hypo-osmotic solution induced an outwardly rectifying Cl- current, which was blocked by NPPB and SITS. This Cl- current did not depend on [Ca2+ ]i because it was still observed when 20 mM BAPTA was included in the pipette, but it did exhibit rundown when ATP was omitted. Inhibition of tyrosine kinases with genistein or tyrphostin A23 (but not the inactive agents daidzein and tyrphostin A1) blocked the Cl- current. The MAP kinase kinase (MEK) inhibitor PD 98059 reversibly inhibited activation of the Cl- current by hypo-osmotic solution. Western immunoblots showed that genistein or PD 98059 blocked activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocytes. Therefore, activation of tyrosine and MAP kinases by swelling is a critical step in the opening of volume-sensitive Cl- channels.

Effects of diadenosine tetraphosphate on FGF9-induced chloride flux changes in achondroplastic chondrocytes

“…The use of a selective inhibitor of ERK1/2 activity showed that ERK1/2 phosphorylation takes part in the decrease in chloride flux observed after FGF9 exposure. The relationship between mitogen-activated protein kinase pathway and chloride current modulation has already demonstrated in astrocytes and cardiac myocytes [28,29].…”

Hydrogen Peroxide Potentiates Volume-sensitive Excitatory Amino Acid Release via a Mechanism Involving Ca2+/Calmodulin-dependent Protein Kinase II

“…Intracellular Signaling Mechanisms Involved in the H 2 O 2 Effect on EAA Release-H 2 O 2 activates non-receptor tyrosine kinases of the src family, receptor tyrosine kinases, and, downstream, enzymes of the MAPK cascade (22,39), all of which have been found to contribute to VRAC activation (23)(24)(25). Therefore, we tested for the contribution of tyrosine and MAP kinases in mediating the H 2 O 2 effect on swelling-induced EAA release.…”

“…In line with such a suggestion, reactive oxygen species positively modulate the activity of a number of protein kinases, such as tyrosine kinases, mitogen-activated protein kinases (MAPKs), protein kinase C (PKC), and Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) (20 -22). All of these kinases have been found to contribute to VRAC activation and/or modulation in a variety of cell types (9,(23)(24)(25)(26)(27)(28). Robust changes in tyrosine phosphorylation and MAPK activity, as well as the translocation of PKC and CaMKII from the cytosol to the membrane fraction, have been found in ischemia (29 -32).…”

Differential dependence of regulatory volume decrease behavior in rabbit corneal epithelial cells on MAPK superfamily activation

“…Several studies have shown that PD98059-but not SB203580-reversibly blocks hypotonic solution activation of the swelling-sensitive Cl − current in astrocytes (Crepel et al, 1998), cardiac muscle (Du and Sorota, 2000) and cervical cancer cells (Shen et al, 2001). PD98059 also blocks swelling-sensitive K + efflux without affecting the KCC co-transporter (Shen et al, 2001).…”