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

1. One of the early events in O-2 chemoreception is inhibition of O-2-sensitive K+ (K-O2) channels. Characterization of the molecular composition of the native K-O2 channels in chemosensitive cells is important to understand the mechanism(s) that couple O-2 to the K-O2 channels. 2. The rat phaeochromocytoma PC12 clonal cell line expresses an O-2-sensitive voltage-dependent K+ channel similar to that recorded in other chemosensitive cells. Here we examine the possibility that the Kv1.2 alpha-subunit comprises the K-O2 channel in PC12 cells. 3. Whole-cell voltage-clamp experiments showed that the K-O2 current in PC12 cells is inhibited by charybdotoxin, a blocker of Kv1.2 channels. 4. PC12 cells express the Kv1.2 alpha-subunit of K+ channels: Western blot analysis with affinity-purified anti-Kv1.2 antibody revealed a band at similar to 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 K-O2 current, while the anti-Kv2.1 and irrelevant antibodies had no effect. 6. The O-2 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 K-O2 channel in PC12 cells belongs to the Kv1 subfamily of K+ channels and that the Kv1.2 alpha-subunit is important in conferring O-2 sensitivity to this channel.