Stimulatory regulation of the large-conductance, calcium-activated potassium channel by G proteins in bovine adrenal chromaffin cells.
G proteins regulate the electrical activity of various cells through their actions on membrane ion channels. In the present study, the effect of G proteins was examined on unitary, large conductance (BK), Ca(2+)-activated K+ channels measured in excised, inside-out patches of membrane obtained from cultured bovine adrenal chromaffin cells. Cytoplasmic application of either guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or AlF-4 to stimulate G proteins resulted in a > 4-fold increase in the open probability of the BK channel measured at +40 mV in the presence of a 1 microM concentration of Ca2+. A similar stimulatory regulation was observed after the addition of an activated, mixed Gi/Go alpha preparation. The increase in the open probability during G protein stimulation was associated with a large reduction in the duration of a long closed state of the channel and could be observed in the presence of a protein kinase inhibitor. The half-maximal voltage required for steady state activation of the BK channel decreased from +63 mV to +48 mV in the presence of GTP gamma S. In addition, the half-maximal Ca2+ concentration required for channel opening was reduced from 11.7 microM in control measurements to 1.3 microM during regulation by GTP gamma S. Thus, G proteins increase the open probability of the chromaffin BK Ca(2+)-activated K+ channel by shifting the voltage dependence of channel gating to more negative potentials and by enhancing the affinity of the channel for Ca2+. Stimulatory regulation may provide a compensatory mechanism for decreasing the action potential duration during secretagogue-mediated exocytosis.
Walsh
K B
KB
Department of Pharmacology, University of South Carolina, School of Medicine, Columbia 29208, USA.
Wilson
S P
SP
Long
K J
KJ
Lemon
S C
SC
D000313:Adrenal Medulla / Q000187:drug effects / Q000502:physiology*; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006706:Homeostasis; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D017607:Aluminum Compounds; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D010566:Virulence Factors, Bordetella; C050992:tetrafluoroaluminate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D005459:Fluorides; D002118:Calcium