Effects of kinase inhibitors on TGF-beta induced upregulation of Kv1.3 K+ channels in brain macrophages.

Deactivation of brain macrophages (microglia) by transforming growth factor-beta (TGF-beta) is characterized by enhanced Kv1.3 K+ channel expression. The intracellular mechanisms by which TGF-beta causes K+ channel upregulation in microglia have remained unclear. We show here that the protein kinase inhibitor H7 abolishes TGF-beta-induced increases in delayed rectifier K+ current density. However, this effect cannot be related to inhibition of protein kinase C (PKC) or protein kinase A (PKA) activity, because specific PKC and PKA inhibitors did not exhibit effects identical to H7. TGF-beta-induced Kv1.3 channel expression was also unaffected by inhibitors of tyrosine kinase, Ca2+/calmodulin kinase II and mitogen-activated protein (MAP) kinase ERK. In contrast, delayed rectifier K+ current density was larger in TGF-beta-stimulated cells pretreated with the p38 MAP kinase inhibitor SB203580 or the phosphatidylinositol 3-OH (PI3) kinase inhibitor wortmannin, suggesting that both p38 MAP kinase and PI3 kinase regulate negatively the upregulation of Kv1.3 K+ channels in TGF-beta-treated microglial cells.