Kvβ1.2 subunit coexpression in HEK293 cells confers O2 sensitivity to Kv4.2 but not to Shaker channels

Voltage-gated K+ (K-v) channels are protein complexes composed of ion-conducting integral membrane or subunits and cytoplasmic modulatory beta subunits. The differential expression and association of alpha and beta subunits seems to contribute significantly to the complexity and heterogeneity of K-v channels in excitable cells, and their functional expression in heterologous systems provides a tool to study their regulation at a molecular level. Here, we have studied the effects of Kv beta 1.2 coexpression on the properties of shaker and Kv4.2 K-v channel alpha subunits, which encode rapidly inactivating A-type K+ currents, in transfected HEK293 cells. We found that Kv beta 1.2 functionally associates with these two cr subunits, as well as with the endogenous K-v channels of HEK293 cells, to modulate different properties of the heteromultimers. Kv beta 1.2 accelerates the rate of inactivation of the Shaker currents, as previously described, increases significantly the amplitude of the endogenous currents, and confers sensitivity to redox modulation and hypoxia to Kv4.2 channels. Upon association with Kv beta 1.2, Kv4.2 can be modified by DTT (1,4 dithiothreitol) and DTDP (2,2'-dithiodipyridine), which also modulate the low pO(2) response of the Kv4.2+beta channels. However, the physiological reducing agent GSH (reduced glutathione) did not mimic the effects of DTT. Finally, hypoxic inhibition of Kv4.2 + beta currents can be reverted by 70% in the presence of carbon monoxide and remains in cell-free patches, suggesting the presence of a hemoproteic O-2 sensor in HEK293 cells and a membrane-delimited mechanism at the origin of hypoxic responses. We conclude that beta subunits can modulate different properties upon association with different K-v channel subfamilies; of potential relevance to understanding the molecular basis of low pO(2) sensitivity in native tissues is the here described acquisition of the ability of Kv4.2+beta channels to respond to hypoxia.