G protein control of potassium channel activity in a mast cell line.

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Abstract
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 AlF4-) completely inhibited the inward rectifier K+ conductance with a half-time for decline averaging .apprx. 300 s after "break-in" to achieve whole-cell recording. In addition, with a half-time averaging .apprx. 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 .apprx. 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 activity by the second messengers Ca2+, inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, or by cyclic AMP-dependent phosphorylation. Pretreatment of the cells with pertussis toxin (0.1 .mu.g/ml for 12-16 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.

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