The pharmacology of ATP-sensitive potassium channels.

A potassium (K) channel that was inhibited by physiological (f1M) concen­ trations of intracellular ATP ([ATP]i) and that opened as [ATP]i decreased was first described in the heart ( l). Subsequently, similar K -channels all with unitary conductances in the range of 40-80 pS (measured under symmetrical high K+ conditions) were also found to exist in insulin-secreting cells and in skeletal muscle (2_5).1 Such channels constitute what are classically described as ATP-sensitive K-channels and were termed Type 1 by Ashcroft & Ashcroft (6). In this review they are designated KATP and the current flowing through them is defined as IK(ATP) . Type 1 KATP channels are essentially calciumand voltage-independent, K+ -selective, and are half-maximally inhibited by [ATP]i in the range 10-100 fJ.M. They exhibit inward rectification and a key pharmacological feature is their inhibition by agents like tolbutamide and glyburide . Other ATP-sensitive K-channels exist and these were designated Types 2, 3, 4, and 5 (6). Such channels vary not only in their sensitivity to calcium and to the inhibitory effects of [ATP]i, but also in their selectivity for potassium and their susceptibility to pharmacological modulation.