K-ATP channels: Linker between phospholipid metabolism and excitability

ATP-sensitive potassium (K-ATP) channels couple electrical activity to cell ular metabolism via their inhibition by intracellular ATP. When examined in excised patches, ATP concentrations required for half-maximal inhibition ( IC50) varied among tissues and were reported to be as low as 10 mu M. This set up a puzzling question on how activation of K-ATP channels can occur un der physiological conditions, where the cytoplasmic concentration of ATP is much higher than that required for channel inhibition. A new twist was add ed to this puzzle when two recent reports showed that phospholipids such as phosphatidylinositol-4,5-bisphosphate (PIP2) and phosphatidyl-4-phosphate (PIP) are able to shift ATP sensitivity of K-ATP channels from the micro- i nto the millimolar range and thus provide a mechanism for physiological act ivation of the channels. This commentary describes how phospholipids contro l ATP inhibition of K-ATP channels and how this mechanism is regulated effe ctively by receptor-mediated stimulation of phospholipase C. (C) 2000 Elsev ier Science Inc.