ATP-inhibited K+ channels and membrane potential of identified leech neurons

The effect of the ATP-inhibited K+ channel on the membrane potential of leech Retzius neurons was analyzed using electrolyte-filled single-barrelled microelectrodes. The membrane potential was independent of the external nutrient supply during a period of 11 h, probably because the internal energy reserves were sufficient. The K+ channel activator HOE 234 ((3S,4R)-3-hydroxy-2, 2-dimethyl-4-(2-oxo-1-pyrrolidinyl)-6-phenylsulfonylchromane hemihydrate, 500 microM) induced a membrane hyperpolarization. In the presence of HOE 234, action potentials occurred with a reduced after-hyperpolarization and were discharged in bursts, possibly because of an inhibition of Ca2+ channels. The blocker of ATP-inhibited K+ channels tolbutamide did not significantly alter the membrane potential. In the absence of tolbutamide, the metabolic inhibitors iodoacetate, azide and cyanide (10 mM) evoked membrane hyperpolarizations, but in the presence of 1 mM tolbutamide their hyperpolarizing actions were reduced or abolished while membrane depolarizations were intensified. We conclude that ATP-inhibited K+ channels in the soma membrane of leech Retzius neurons provide coupling of cellular metabolism to electrical activity and ionic fluxes.