A New TASK for Dipeptidyl Peptidase-like Protein 6
Figure 2
DPP6 regulates an outwardly rectifying resting membrane potassium conductance.
CG cells were treated with lentiviral vectors expressing EGFP (control: WT (n = 32); Kv4.2 KO (n = 9)) or mDPP6 RNAi (WT (n = 13), Kv4.2 KO (n = 6)) to knockdown DPP6. For rescue experiments the lentiviral vectors also co-expressed rat DPP6 (rDPP6), which is insensitive to the mouse DPP6 RNAi due to coding differences in the RNAi target sequence. Both rDPP6K and rDPP6a splice variants, which are highly expressed in CG cells, were tested (rDPP6K: WT (n = 32); rDPP6a: WT (n = 31), Kv4.2 KO (n = 4)). A) Knockdown of mDPP6 causes a depolarization of the resting membrane potential which is reversed by co-expression of rDPP6. Results for wild type and Kv4.2 KO animals are indistinguishable (NSD: control (P = 0.33); mDPP6 RNAi (P = 0.72); rDPP6a (P = 0.85)). (data plotted ± SEM). B) Resting input resistance is increased for CG cells following RNAi treatment and this effect is reversed by co-expression of rDPP6. Results between CG cells from control and Kv4.2 KO animals are indistinguishable (NSD: control (P = 0.15); mDPP6 RNAi (P = 0.74); rDPP6a (P = 0.72)). (data plotted ± SEM). C) Average membrane current versus membrane potential for control (n = 24) and mDPP6 RNAi (n = 13) treated CG cells. Knockdown of DPP6 reduces the amplitude of an outwardly rectifying current (P = 0.0002). Smooth curves were generated with NEURON using the following conductances (mDPP6 RNAi: GK2P = 60 nS; GL = 0.133 nS; Control: Same+GTASK-3 = 30 nS). Inset expands the axes near the resting membrane potential to show that a linear Ohmic fit to this current can explain the change in input resistance (Slope change) and Erest (0 current potential shift). (data plotted ± SEM). D) Difference current for mDPP6 RNAi treated cells compared to control shows that the RNAi sensitive current is outwardly rectifying and reverses near −90 mV as expected for a potassium selective conductance. (data plotted ± SEM). Smooth curve shows TASK-3 model fit to the data (GTASK-3 = 30 nS). e) Representative voltage clamp traces show that the conductance regulated by mDPP6 RNAi is outwardly rectifying similar to IK(SO) conductance previously described in CG cells. Scale bar: 200 pA, 100 ms.