Glucocorticoid Regulation of Calcium-activated Potassium Channels Mediated by Serine/Threonine Protein Phosphatase

• Published in: The Journal of biological chemistry Vol. 273; no. 22; pp. 13531 - 13536
• Main Authors: Tian, Lijun, Knaus, Hans-Guenther, Shipston, Michael J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 29.05.1998; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Calcium - pharmacology; Cell Line; Cyclic AMP-Dependent Protein Kinases - metabolism; Dexamethasone - pharmacology; Enzyme Inhibitors - pharmacology; Large-Conductance Calcium-Activated Potassium Channels; Mice; Okadaic Acid - pharmacology; Patch-Clamp Techniques; Phosphoprotein Phosphatases - antagonists & inhibitors; Phosphoprotein Phosphatases - metabolism; Potassium Channels - drug effects; Potassium Channels - metabolism; Potassium Channels, Calcium-Activated; Protein Phosphatase 2
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.22.13531

Adrenal glucocorticoids exert powerful effects on cellular excitability in neuroendocrine cells and neurons, although the underlying mechanisms are poorly understood. In metabolically intact mouse anterior pituitary corticotrope (AtT20) cells glucocorticoid-induced proteins render large conductance calcium-activated potassium (BK) channels insensitive to inhibition by protein kinase A (PKA). In this study we have addressed whether this action of glucocorticoids is mediated via protein phosphatase activity at the level of single BK channels. In isolated inside-out patches from control AtT20 cells BK channels (125 pS) were inhibited by activation of closely associated PKA. Pretreatment (2 h) of cells with 1 μm dexamethasone before patch excision did not modify the intrinsic properties or expression levels of BK channel α-subunits in AtT20 cells. However, PKA-mediated inhibition of BK channel activity in isolated patches from steroid-treated cells was severely blunted. This effect of steroid was not observed using adenosine 5′-O-(3-thiotriphosphate) as phosphate donor or on exposure of the intracellular face of the patch with 10 nm of the protein phosphatase inhibitors okadaic acid or calyculin A but was mimicked by application of protein phosphatase 2A (PP2A) to the intracellular face of patches from control cells. Glucocorticoids did not modify total PP2A activity in AtT20 cells, suggesting that modified PP2A-like phosphatase activity closely associated with BK channels is required for glucocorticoid action.