Kv11.1 (ERG1) K+ Channels Localize in Cholesterol and Sphingolipid Enriched Membranes and Are Modulated by Membrane Cholesterol

Abstract

The localization of ion channels to specific membrane microdomains can impact the functional properties of channels and their role in cellular physiology. We determined the membrane localization of human Kv11.1 (hERG1) α -subunit protein, which underlies the rapidly activating, delayed rectifier K+ current (IKr) in the heart. Immunocytochemistry and membrane fractionation using discontinuous sucrose density gradients of adult canine ventricular tissue showed that Kv11.1 channel protein localized to both the cell surface and T-tubular sarcolemma. Furthermore, density gradient membrane fractionation using detergent (Triton X-100) and non-detergent (OptiPrep) methods from canine ventricular myocytes or HEK293 cells demonstrated that Kv11.1 protein, along with MiRP1 and Kv7.1 (KCNQ1) proteins, localize in cholesterol and sphingolipid enriched membrane fractions. In HEK293 cells, Kv11.1 channels, but not long QT-associated mutant G601S-Kv11.1 channels, also localized to cholesterol and sphingolipid enriched membrane fractions. Depletion of membrane cholesterol from HEK293 cells expressing Kv11.1 channels using methyl-Mβ -cyclodextrin (Mβ CD) caused a positive shift of the voltage dependence of activation and an acceleration of deactivation kinetics of Kv11.1 current (IKv11.1). Cholesterol loading of HEK293 cells reduced the steep voltage dependence of IKv11.1 activation and accelerated the inactivation kinetics of IKv11.1. Incubation of neonatal mouse myocytes in Mβ CD also accelerated the deactivation kinetics of IKr. We conclude that Kv11.1 protein localizes in cholesterol and sphingolipid enriched membranes and that membrane cholesterol can modulate IKv11.1 and IKr.