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J Biol Chem, Vol. 273, Issue 22, 13531-13536, May 29, 1998
From the Membrane Biology Group, Department of Physiology, Medical
School, Teviot Place, University of Edinburgh, Edinburgh, Scotland, EH8
9AG, United Kingdom and the 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
Glucocorticoid Regulation of Calcium-activated Potassium Channels
Mediated by Serine/Threonine Protein Phosphatase
, and Institut Fuer Biochemische
Pharmakologie, Peter Mayr-Strasse 1, A-6020 Innsbruck, Austria
-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.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.
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