Fig. 5.

βγ-interacting peptide (peptide G) inhibits the potassium current response. A, Reduction of the response to dopamine after injection of peptide G (79 ± 4%;n = 5) or injection of carrier (8 ± 1%;n = 3). *p < 0.001; unpairedt test. B, Induction of the sustained K⁺ current as a result of irreversible activation of the G-protein. Repeated application of agonist with 200 μm GTP-γ-S in the pipette induces a sustained current (b), which is the irreversible part of the response. In the right panel, it is also seen as the increased holding current before the response. Shown are the first and last response to the agonist, in this example FMRFa;arrows indicate application of agonist during the step to −40 mV. The sustained current is only detected at −40 mV, when the driving force for potassium is large. Notice that the holding current at −80 mV (a) remains constant.C1, Effect of peptide G on the sustained potassium current, induced as in B, using dopamine as agonist. Sustained current amplitude was measured once every 2 min. Injection of peptide G (indicated by arrow) is done after the last dopamine application. (Concentration of peptide G in injection electrode was 5 mm, and final concentration is estimated to be ≤50 μm.) C2, Example trace of the immediate effect of peptide G on the sustained current at −40 mV.Arrow marks injection of peptide G. C3, Like B2 but with injection of carrier instead of peptide G. Obviously, the carrier has no effect.