Hormonal regulation of pituitary GH3 cell K+ channels by Gk is mediated by its alpha-subunit

The resolved alpha-GTP gamma S (alpha*) and beta gamma-subunits of human erythrocyte Gk, the stimulatory regulatory component of hormone-responsive K+ channels, were tested for their potential stimulatory activities on the K+ channel of the endocrine GH3 cell. Concentrations as low as 0.5 pM alpha k* consistently activated K+ channels in isolated membrane patches, and saturating effects were obtained with 50 pM alpha k*. In contrast 2000-4000 pM beta gamma was without effect. We conclude that Gk acts on K+ channels through its alpha-subunit in a manner akin to that of Gs acting on adenylyl cyclase and transducin acting on cGMP-specific phosphodiesterase of photo-receptor cells.