ATP-inhibited and Ca(2+)-dependent K+ channels in the soma membrane of cultured leech Retzius neurons.

The properties of one ATP-inhibited and one Ca(2+)-dependent K+ channel were investigated by the patch-clamp technique in the soma membrane of leech Retzius neurons in primary culture. Both channels rectify at negative potentials. The ATP-inhibited K+ channel with a mean conductance of 112 pS is reversibly blocked by ATP (Ki = 100 microM), TEA (Ki = 0.8 mM) and 10 mM Ba2+ and irreversibly blocked by 10 nM glibenclamide and 10 microM tolbutamide. It is Ca2+ and voltage independent. Its open state probability (Po) decreases significantly when the pH at the cytoplasmic face of inside-out patches is altered from physiological to acid pH values. The Ca(2+)-dependent K+ channel with a mean conductance of 114 pS shows a bell-shaped Ca2+ dependence of Po with a maximum at pCa 7-8 at the cytoplasmic face of the membrane. The Po is voltage independent at the physiologically relevant V range. Ba2+ (10 MM) reduces the single channel amplitude by around 25% (ATP, TEA, glibenclamide, tolbutamide, and Ba2+ were applied to the cytoplasmic face of the membrane). We conclude that the ATP-dependent K+ channel may play a role in maintaining the membrane potential constant--independently from the energy state of the cell. The Ca(2+)-dependent K+ channel may play a role in generating the resting membrane potential of leech Retzius neurons as it shows maximum activity at the physiological intracellular Ca2+ concentration.