A Kir6.2 Mutation Causing Neonatal Diabetes Impairs Electrical Activity and Insulin Secretion From INS-1 β-Cells

Abstract

ATP-sensitive K⁺ channels (K_ATP channels) couple β-cell metabolism to electrical activity and thereby play an essential role in the control of insulin secretion. Gain-of-function mutations in Kir6.2 (KCNJ11), the pore-forming subunit of this channel, cause neonatal diabetes. We investigated the effect of the most common neonatal diabetes mutation (R201H) on β-cell electrical activity and insulin secretion by stable transfection in the INS-1 cell line. Expression was regulated by placing the gene under the control of a tetracycline promoter. Transfection with wild-type Kir6.2 had no effect on the ATP sensitivity of the K_ATP channel, whole-cell K_ATP current magnitude, or insulin secretion. However, induction of Kir6.2-R201H expression strongly reduced K_ATP channel ATP sensitivity (the half-maximal inhibitory concentration increased from ∼20 μmol/l to ∼2 mmol/l), and the metabolic substrate methyl succinate failed to close K_ATP channels or stimulate electrical activity and insulin secretion. Thus, these results directly demonstrate that Kir6.2 mutations prevent electrical activity and insulin release from INS-1 cells by increasing the K_ATP current and hyperpolarizing the β-cell membrane. This is consistent with the ability of the R201H mutation to cause neonatal diabetes in patients. The relationship between K_ATP current and the membrane potential reveals that very small changes in current amplitude are sufficient to prevent hormone secretion.