Figure 7. Deletion of G1-dCT increases P_o and enhances activation by agonist and Gβγ in the GIRK1* homotetrameric channel.

A, cell-attached patch clamp records of GIRK1* channels (left trace) and GIRK1*Δ121 channels (right trace). K⁺ currents are shown as downward deflections from zero current, shown as dashed line. The oocytes expressed the channels in the presence of 5:1 ng per oocyte of Gβ/Gγ. Both patches contained two channels. Note that in GIRK1*Δ121 the second channel appears after >3 min of recording (arrow). The lower traces zoom in on the indicated intervals at an expanded time scale. B and C, summary of P_o (B) and i_single (C) measurements. D–F, whole-cell currents of GIRK1* and GIRK1*Δ121 homomeric channels. Oocytes were injected with 0.2 and 2 ng RNA, respectively, to attain approximately equal levels of expression of the channels. Currents were measured in the 96 mm high-K⁺ solution (see Methods). Summary of current amplitudes is shown in D. The truncated homomeric channel shows a higher R_a (E) and R_βγ (F) than the full-length channel. ***P < 0.001.