ATP-sensitive K+ channels (K-ATP:SUR2A + Kir6.2) play a pivotal role in cardiac protection against ischemia and reperfusion injury. When expressed in COS cells, Kir6.2 was short-lived with a half-life time of 1.9 h. The half-life time of Kir6.2 was prolonged by proteasome inhibitors MG132, ALLN, proteasome inhibitor 1, and lactacystine, but not at all by a lysosomal inhibitor chloroquine. MG132 also increased the level of ubiquitinated Kir6.2 without affecting its localization in the endoplasmic reticulum and Golgi apparatus. In electrophysiological recordings, MG132 augmented nicorandil-activated K-ATP currents in COS cells expressing SUR2A and Kir6.2 as well as the sane currents in neonatal rat cardiomyocytes. Like MG132, a Na+ channel blocker aprindine prolonged the half-life time of Kir6.2 and augmented K-ATP. Finally, both aprindine and MG 132 inhibited the 20S proteasome activity in vitro. These results suggest a novel activity of aprindine to enhance K-ATP currents by inhibiting proteasomal degradation of Kir6.2 channels, which may be beneficial in the setting of cardiac ischemia. (c) 2005 Elsevier Inc. All rights reserved.