Selective Formation of Oligomeric Kv7.5 (KCNQ5)/KCNE1 and Kv7.5 (KCNQ5)/KCNE3 Channels. Differential Targeting to Membrane Surface Microdomains

Abstract

Kv7 (KCNQ) proteins form a family of voltage-gated potassium channels that is comprised of five members, Kv7.1-Kv7.5. While Kv7.1 is crucial in the heart, the Kv7.2-Kv7.5 channels contribute to the M-current in the nervous system. In addition, Kv7.5 is expressed in muscles, where its physiological role is currently under evaluation. Kv7 associations with KCNE accessory subunits (KCNE1-5) enhance channel diversity. KCNE peptides control the surface expression, voltage-dependence, kinetics of gating, unitary conductance, ion selectivity and pharmacology of several channels. KCNE subunits have been primarily studied in the heart; however, their activity in the brain and in many other tissues is being increasingly recognized. Here, we found that Kv7.5 and KCNE subunits are present in myoblasts. Therefore, oligomeric associations may underlie some Kv7.5 functional diversity in skeletal muscle. Expression in Xenopus oocytes and HEK-293 cells demonstrates that KCNE1 and KCNE3, but none of the other KCNE subunits, associate to Kv7.5. While KCNE1 slows activation and suppresses inward rectification, KCNE3 inhibits Kv7.5 currents. Furthermore, KCNE1 increases Kv7.5 currents in HEK cells. The membrane targeting is also affected. Biochemical isolation of lipid rafts demonstrates that Kv7.5 barely locates in rafts. KCNE1 and KCNE3 show differential targeting. While KCNE3 targets to rafts, KCNE1 does not. Association of Kv7.5 with KCNE3 impairs KCNE3 targeting to rafts and this is further supported by FRAP analysis. Our results have physiological relevance since Kv7.5 is abundant in skeletal and smooth muscle and its association with KCNE peptides may fine-tune cellular responses.Supported by the Ministerio de Ciencia e Innovacion (MICINN), Spain (BFU2005-00695, BFU2008-00431 and CSD2008-00005).