Figure 1.

Inhibition of the ATP-induced changes in K_ACh channel function by atrial cytosolic fraction (CF). (A) Activation of K_ACh channels in atrial outside-out patches by 10 μM ACh. Pipette solution contained nucleotides as indicated: 100 μM GTP, 100 μM GTP and 4 mM ATP, or 100 μM GTP, 4 mM ATP, and 5 mg protein/ml CF. (B) With 10 μM ACh in the pipette, K_ACh channels in inside-out patches were activated by 100 μM GTP. Subsequent effects of 4 mM ATP, atrial CF, and cramming of the patch into an atrial cell cytoplasm are shown. Membrane potential was held at −60 mV and inward currents were recorded.