G protein control of potassium channel activity in a mast cell line.
Using the patch-clamp technique, we studied regulation of potassium channels by G protein activators in the histamine-secreting rat basophilic leukemia (RBL-2H3) cell line. These cells normally express inward rectifier K+ channels, with a macroscopic whole-cell conductance in normal Ringer ranging from 1 to 16 nS/cell. This conductance is stabilized by including ATP or GTP in the pipette solution. Intracellular dialysis with any of three different activators of G proteins (GTP gamma S, GppNHp, or AlF-4) completely inhibited the inward rectifier K+ conductance with a half-time for decline averaging approximately 300 s after "break-in" to achieve whole-cell recording. In addition, with a half-time averaging approximately 200 s, G protein activators induced the appearance of a novel time-independent outwardly rectifying K+ conductance, which reached a maximum of 1-14 nS. The induced K+ channels are distinct from inward rectifier channels, having a smaller single-channel conductance of approximately 8 pS in symmetrical 160 mM K+, and being more sensitive to block by quinidine, but less sensitive to block by Ba2+. The induced K+ channels were also highly permeable to Rb+ but not to Na+ or Cs+. The current was not activated by the second messengers Ca2+, inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, or by cyclic AMP-dependent phosphorylation. Pretreatment of cells with pertussis toxin (0.1 microgram/ml for 12-13 h) prevented this current's induction both by guanine nucleotides and aluminum fluoride, but had no effect on the decrease in inward rectifier conductance. Since GTP gamma S is known to stimulate secretion from patch-clamped rat peritoneal mast cells, it is conceivable that K+ channels become inserted into the plasma membrane from secretory granules. However, total membrane capacitance remained nearly constant during appearance of the K+ channels, suggesting that secretion induced by GTP gamma S was minimal. Furthermore, pertussis toxin had no effect on secretion triggered by antigen, and triggering of secretion before electrical recording failed to induce the outward K+ current. Finally, GTP gamma S activated the K+ channel in excised inside-out patches of membrane. We conclude that two different GTP-binding proteins differentially regulate two subsets of K+ channels, causing the inward rectifier to close and a novel K+ channel to open when activated.
McCloskey
M A
MA
Department of Physiology and Biophysics, University of California, Irvine 92717.
Cahalan
M D
MD
D000535:Aluminum / Q000494:pharmacology*; D017607:Aluminum Compounds; D000818:Animals; D002460:Cell Line; D005459:Fluorides; D005461:Fluorine / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology*; D015471:Leukemia, Basophilic, Acute / Q000503:physiopathology*; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology*; D009431:Neural Conduction / Q000187:drug effects*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology*
D017607:Aluminum Compounds; D015221:Potassium Channels; D013873:Thionucleotides; C050992:tetrafluoroaluminate; D005461:Fluorine; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D000535:Aluminum; D019204:GTP-Binding Proteins; D005459:Fluorides