Mechanism of Carbamazepine Mediated Rescue of Trafficking Defective Mutant KATP Channels

Abstract

The β-cell ATP-sensitive potassium (KATP) channel regulates insulin secretion by coupling glucose metabolism to membrane excitability. Mutations in the constituent protein subunits Kir6.2 and sulfonylurea receptor 1 (SUR1) that prevent channels from trafficking to the cell surface are frequent causes of congenital hyperinsulinism. We recently reported that carbamazepine, an anticonvulsant, corrects the trafficking defects caused by mutations in the N-terminal transmembrane domain of SUR1. In addition, carbamazepine inhibits the function of rescued channels that can be reversed by subsequent drug removal. Here, we investigated the mechanism underlying carbamazepine's effects on KATP channel trafficking and gating by partial proteolysis and electrophysiology, respectively. We show that carbamazepine inhibits channel activity by specifically abolishing channel response to the physiological stimulator MgADP. Our partial proteolysis results show that carbamazepine interacts with the channel complex and protects the N-terminus of Kir6.2 against trypsin digestion. Further, results show that deletion of Kir6.2 N-terminal 30 amino acids severely compromised carbamazepine mediated rescue of the SUR1 trafficking mutant, F27S. Our findings suggest a structural model for carbamazepine mediated rescue of SUR1-TMD0 trafficking mutants and inhibition of KATP channels.