Protein kinase C involvement in the resting and interferon-γ-induced K+ channel profile of microglial cells
✍ Scribed by Sergio Visentin; Giulio Levi
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 189 KB
- Volume
- 47
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
The whole-cell configuration of the patch-clamp technique was used to study the involvement of protein kinase C (PKC) in the modulation of K 1 channels in cultured microglia from newborn rats. We previously showed that 24-hr treatments with interferon-g (IFN-g) induce an increase of inward-rectifying (IR) and outward-rectifying (OR) current density and that the effect on OR was shared by bacterial lipopolysaccharide (LPS) (Visentin et al.: J Neurosci Res 42:439-451, 1995). In the present study, IFN-g (1-500 U/ml, 24 hr) enhanced IR current density up to threefold. The IFN-g effect was not detectable after shorter treatments (1-5 hr) and was abrogated by a protein synthesis inhibitor. The PKC activator phorbol myristate acetate (PMA) also increased IR current density, whereas the inactive a-4 isoform was ineffective. When IFN-g and PMA were co-applied, the effect was more than additive. Among the PKC inhibitors tested, staurosporine (STA)-but not calphostin C (CALP)abolished the effect of IFN-g and of PMA and antagonized only partially that of co-applied IFN-g and PMA. OR currents were affected by treatment (24 hr) with PKC modulating agents in an opposite fashion. PMA depressed OR currents in control and in IFN-g (or LPS) treated cultures, even when added after pretreatment (with LPS) that was long enough to enhance OR channel expression. Both STA and CALP enhanced OR density in resting and IFN-g-stimulated cells but did not counteract the depressing effect of PMA. In conclusion, our data on IR suggest a relationship between the IFN-g effect on current density and PKC activation. However, we cannot conclude with certainty that IFN-g acts through PKC activation. Our data on OR support an inverse relationship between PKC activation and OR current density. Nevertheless, the lack of effect of PKC inhibitors on PMA-induced OR depression suggests that PMA may, in this case, act on a target different from PKC. J.