Mechanisms on the degradation of ion channel proteins and their modification by antiarrythmic agents

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Background: The voltage gated potassium channel Kv1.5 plays a critical role in the maintenance of the membrane potential and cardiac Kv1.5 is of particular clinical importance as a target of various antiarrhythmic drugs. While protein degradation is one of the major mechanisms to regulate channel protein functions, little is known on the degradation mechanism of Kv1.5 proteins was estimated by pulse chase an alysis, immnofluorescence and patch clamp techniques in transfected COS cells and rat atrial myocytes. Expressed Kv1.5 had a short half-life time of 6.7h. Aproteasome inhibitor MG132, but not a lysosome inhibitor chloroquine, significantly prolonged the half-life time and increased the levels of both total proteins and ubiquitinated proteins. Kv1.5 was mainly localized in the endoplasmic reticulum and Golgi apparatus. MG132 increased the levels of Kv1.5 proteins in these compartments, causing a significant in Ik_<ur>currents through the cell-surface Kv1.5. The effect of MG132 on Ik … More _<ur>currents was abolished both by brefeldine A and colchicine. Like MG132, Na^+channel blockers pilsicainide and lidocaine prolonged the half-life time of Kv1.5 and increased both protein levels and IK_<ur>currents. Neither a K^+channel blocker E-4031 nora Ca^<2+>channel blocker verapamil exerted these effects. Similarly, both Na^+channel blockers and MG132 increased the level of Kv1.5 in primary-cultured rat atrial myocytes. These Na^+ channel blockers inhibited the 20S proteasome activity in vitro and also stabilized the IkB2 protein expressed in COS cells. Conclusion: Kv1.5 is ubiquitinated and degraded by the proteasome. Na^+ channel blockers pilsicainide and lidocaine, by mimicking the action of MG132, could stabilize Kv1.5 and increase Ik_<ur>currents, suggesting a novel pharmacological action of these agents to inhibitproteasomal degradation of K^+channel proteins. These drugs possess a novel pharmacological activity to inhibit the proteasome, suggesting effect of the Na^+channel blockers is not specific to Kv1.5 but may extend to other proteins destined to proteasomal degradation. Less