Figure 2.

GIRK1/GIRK4 and GR7.1 currents are activated via similar membrane-delimited pathways. Cell-attached patches containing multiple channels from oocytes expressing GIRK1/GIRK4 (A), RB-IRK2 (B), or chimera GR7.1 (C), were held at −60 mV for 800 ms, and then depolarized to +60 mV for 800 ms every 5 s for the duration of the experiment. Carbachol was added to the bath at the indicated time by hand pipetting. Carbachol was perfused into the pipet by suction (see Materials and Methods) over the indicated time period. Each point on the larger plot represents the integrated current over the portion of the trace at one holding potential for that time point. The insets show representative traces from before the addition of carbachol to the bath (left), after addition to the bath (center), and after addition to the pipet (right). The transient increase in outward current during the perfusion reflects activation of the oocyte's endogenous stretch-activated channels by the suction applied to the pipet. D shows the average percent change in integrated current after carbachol addition to the bath and to the pipet for GR7.1 (filled bars, n = 5) and RB-IRK2 (open bars, n = 5); error bars represent SEM. Because there is virtually no current before addition of carbachol to the pipet for GIRK1/GIRK4, the percent change is undefined.