Modulation of nucleotide sensitivity of ATP-sensitive potassium channels by phosphatidylinositol-4- phosphate 5-kinase

摘要

ATP-sensitive potassium channels (KATP channels) regulate cell excitability in response to metabolic changes. KATP channels are formed as a complex of a sulfonylurea receptor (SURx). a member of the ATP-binding cassette protein family. and an inward rectifier K+ channel subunit (Kir6.x). Membrane phospholipids, in particular phosphatidylinositol (PI) 4.S-bisphosphate (PlP2). activate KATP channels and antagonize ATP inhibition of KATP channels when applied to inside-out membrane patches. To examine the physio- logical relevance of this regulatory mechanism, we manipulated membrane PlP2 levels by expressing either the wild-type or an inactive form of Pl-4-phosphate S-kinase (PlP5K) in COSm6 cells and examined the ATP sensitivity of coexpressed KATP channels. Chan- nels from cells expressing the wild-type PIP5K have a 6-fold lower ATP sensitivity (K1/2. the half maximal inhibitory concentration, ca 60 pM) than the sensitivities from control cells (K1/2 rs 10 yM). An inactive form of the PIP5K had little effect on the K1/2 of wild-type channels but increased the ATP-sensitivity of a mutant KATP chan- nel that has an intrinsically lower ATP sensitivity (from K1/2 se 450 pM to Kl/z rs 100 pM), suggesting a decrease in membrane PlP2 levels as a consequence of a dominant-negative effect of the inactive PlP5K. These results show that PlP5K activity. which regulates PlP2 and Pl-3.4,5-P3 levels, is a significant determinant of the physiological nucleotide sensitivity of KATP channels.