Phosphatase activity of Ci-VSP monitored by the activity of the potassium-selective, voltage-, and PI(4,5)P2-dependent channels KCNQ2 and KCNQ3. (A) Currents of KCNQ2/3 expressed without Ci-VSP. (B) When KCNQ2/3 were expressed with the WT form of Ci-VSP, a strong decrease in the activity was observed at potentials above +20 mV. (C) Coexpression with the mutant R253A-R254A caused a slight decrease in the current of KCNQ2/3, only observable at very positive potentials. (D) Likewise, coexpression with the mutant R245A-R246A caused an initial decrease in the current of the channels at potentials above +80 mV. However, the effect on the ionic current was less profound than that observed with the mutant R253A-R254A. (E) Transient initial currents were not observed when mRNA coding for Ci-VSP was not injected in the oocytes along with the mRNA for KCNQ2/3. (F–H) In contrast, transient initial currents were observed in the presence of the phosphatase. These currents are the sensing currents of Ci-VSP. Pulses range from −100 to +100 mV. HP = −90 mV. For A–C and E–G, the interval between pulses was 10 mV. For D and H, it was 20 mV.
