Figure 3.

The wvGIRK4 channel functions similarly to wvGIRK2. (A Upper) Representative traces from oocytes injected with 5 ng wvGIRK2 mRNA and 3 ng m2AChR mRNA. Bars indicate application of 98 mM Na⁺ or K⁺. (A Lower) Representative traces from oocytes injected with 25 ng wvGIRK4 mRNA and 3 ng m2AChR mRNA. Bars indicate application of 98 mM Na⁺ or K⁺, 1 μM ACh, 100 μM QX-314, or 50 μM MK-801. Where no bar is shown, the bath solution contained 98 mM NMDG as the only monovalent cation. (B) Representative voltage-jump records from an oocyte injected with 25 ng wvGIRK4 mRNA. The membrane potential was held at −80 mV, stepped to −120 mV for 300 ms, then stepped to test potentials between −120 and +40 mV in 20-mV increments for 1500 ms, at intervals of 7 s. The dashed lines indicate zero current. No subtractions were performed, and currents were not corrected for desensitization. The extracellular solution contained 98 mM Na⁺, K⁺, or NMDG as the only monovalent cation. The plot shows current-voltage relations for the voltage-step records, with points taken from immediately before the step back to −80 mV. (C) Variation of constitutive activation with total Na⁺ current for wvGIRK4-injected oocytes incubated in the standard medium. •, wvGIRK4 mRNA alone; □, wvGIRK4 plus either wvGIRK1, GIRK1, or GIRK4. (D) Dose-response relation for QX-314 blockade of wvGIRK4 Na⁺ currents.