Interaction of acetylcholine with Kir6.1 channels heterologously expressed in human embryonic kidney cells

Kir6.1 subunit is one of the pore-forming components of K(ATP) channel complex. The endogenous modulation of Kir6.1 subunit function has been largely unknown. Whether acetylcholine modulated the function of Kir6.1 subunit stably expressed in human embryonic kidney (HEK-293) cells was examined in the present study using the whole-cell patch-clamp technique. Acetylcholine from 1-100 microM concentration-dependently stimulated the heteologously expressed and PNU-37883A sensitive Kir6.1 channels (p<0.05). Co-expression of sulphonylurea receptor 1 subunit with Kir6.1 significantly inhibited the stimulatory effect of acetylcholine on K(ATP) currents. Pretreatment of the transfected HEK-293 cells with atropine, alpha-bungarotoxin, mecamylamine, prazocine, propranolol, or dihydro-beta-erythroidine hydrobromide did not alter the stimulatory effect of acetylcholine on Kir6.1 currents. When intracellular ATP was increased from 0.3 mM to 5 mM, acetylcholine at 10 microM still exhibited its stimulatory effect (-16.4+/-2.3 to -25.5+/-3.8 pA/pF, n=8, p<0.05). In conclusion, we have demonstrated an excitatory effect of acetylcholine on Kir6.1 channels, which is mediated neither by an acetylcholine receptor-dependent mechanism, nor by alteration in ATP metabolism.