Glucocorticoid block of protein kinase C signalling in mouse pituitary corticotroph AtT20 D16:16 cells.
1. The regulation of large conductance calcium- and voltage-activated potassium (BK) currents by activation of the protein kinase C (PKC) and glucocorticoid signalling pathways was investigated in AtT20 D16:16 clonal mouse anterior pituitary corticotroph cells. 2. Maximal activation of PKC using the phorbol esters, 4beta-phorbol 12-myristate, 13-acetate (PMA), phorbol 12, 13 dibutyrate (PDBu) and 12-deoxyphorbol 13-phenylacetate (dPPA) elicited a rapid, and sustained, inhibition of the outward steady-state voltage- and calcium- dependent potassium current predominantly carried through BK channels. 3. The effect of PMA was blocked by the PKC inhibitors bisindolylmaleimide I (BIS; 100 nM) and chelerythrine chloride (CHE; 25 microM) and was not mimicked by the inactive phorbol ester analogue 4alpha-PMA. 4. PMA had no significant effect on the 1 mM tetraethylammonium (TEA)-insensitive outward current or pharmacologically isolated, high voltage-activated calcium current. 5. PMA had no significant effect on steady-state outward current in cells pre-treated for 2 h with 1 microM of the glucocorticoid agonist dexamethasone. Dexamethasone had no significant effect on steady-state outward current amplitude or sensitivity to 1 mM TEA and did not block PMA-induced translocation of the phorbol ester-sensitive PKC isoforms, PKCalpha and PKCepsilon, to membrane fractions. 6. Taken together these data suggest that in AtT20 D16:16 corticotroph cells BK channels are important targets for PKC action and that glucocorticoids inhibit PKC signalling downstream of PKC activation.
Tian
L
L
Membrane Biology Group, Department of Biomedical Sciences, University of Edinburgh, Medical School, Teviot Place, Edinburgh EH8 9AG, UK.
Philp
J A
JA
Shipston
M J
MJ
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004594:Electrophysiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005938:Glucocorticoids / Q000494:pharmacology*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D051379:Mice; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000819:agonists / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects*
D005938:Glucocorticoids; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010703:Phorbol Esters; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011493:Protein Kinase C