O2‐sensitive K+ channels: role of the Kv1.2 α‐subunit in mediating the hypoxic response

1 One of the early events in O2 chemoreception is inhibition of O2‐sensitive K+ (KO2) channels. Characterization of the molecular composition of the native KO2 channels in chemosensitive cells is important to understand the mechanism(s) that couple O2 to the KO2 channels. 2 The rat phaeochromocytoma PC12 clonal cell line expresses an O2‐sensitive voltage‐dependent K+ channel similar to that recorded in other chemosensitive cells. Here we examine the possibility that the Kv1.2 α‐subunit comprises the KO2 channel in PC12 cells. 3 Whole‐cell voltage‐clamp experiments showed that the KO2 current in PC12 cells is inhibited by charybdotoxin, a blocker of Kv1.2 channels. 4 PC12 cells express the Kv1.2 α‐subunit of K+ channels: Western blot analysis with affinity‐purified anti‐Kv1.2 antibody revealed a band at ≈80 kDa. Specificity of this antibody was established in Western blot and immunohystochemical studies. Anti‐Kv1.2 antibody selectively blocked Kv1.2 current expressed in the Xenopus oocyte, but had no effect on Kv2.1 current. 5 Anti‐Kv1.2 antibody dialysed through the patch pipette completely blocked the KO2 current, while the anti‐Kv2.1 and irrelevant antibodies had no effect. 6 The O2 sensitivity of recombinant Kv1.2 and Kv2.1 channels was studied in Xenopus oocytes. Hypoxia inhibited the Kv1.2 current only. 7 These findings show that the KO2 channel in PC12 cells belongs to the Kv1 subfamily of K+ channels and that the Kv1.2 α‐subunit is important in conferring O2 sensitivity to this channel.