title: Activation of protein kinase C inhibits calcium-activated potassium channels in rat pituitary tumour cells.
abstract: 1. The regulation of large-conductance, calcium- and voltage-dependent potassium (BK) channels by protein kinase C (PKC) was investigated in clonal rat anterior pituitary cells (GH4C1), which were voltage clamped at -40 mV in a physiological potassium gradient through amphotericin-perforated patches. 2. Maximal activation of PKC by 100 nM phorbol 12, 13-dibutyrate (PdBu) almost completely inhibited the voltage-activated outward current through BK channels. In contrast PdBu had no significant effect on the residual outward current after block of BK channels with 2 mM TEA or 30 nM charybdotoxin. In single-channel recordings from cell-attached patches, PdBu reduced the open probability of BK channels more than eightfold with no significant effect on mean open lifetime or unitary conductance. 3. The effects of PdBu on BK channels were not mimicked by the 4 alpha-isomer, which does not activate PKC, and were blocked almost completely by 25 microM chelerythrine, a specific, noncompetitive PKC inhibitor. 4. PdBu had no significant effect on the amplitude of the pharmacologically isolated, high voltage-activated calcium current. 5. Inhibition of BK channel activity by PKC provides the first molecular mechanism linking hormonal activation of phospholipase C to sustained excitability in pituitary cells.
authors.affiliation: Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA. mshipston@srv2.med.ed.ac.uk
authors.forename: M J
authors.initials: MJ
authors.lastname: Shipston
authors.forename: D L
authors.initials: DL
authors.lastname: Armstrong
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001711:Biotransformation / Q000187:drug effects; D002118:Calcium / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010911:Pituitary Neoplasms / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured
chemical_list: D000900:Anti-Bacterial Agents; D015221:Potassium Channels; D015240:Phorbol 12,13-Dibutyrate; D000666:Amphotericin B; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium