Modulation of K+ channels by intracellular ATP in human neocortical neurons

ATP-modulated K+ channels play an important role in regulating membrane excitability during metabolic stress. To characterize such K+ channels from the human brain, single channel currents were studied in excised inside-out patches from freshly dissociated human neocortical neurons. Three currents that were sensitive to physiological concentrations of ATP and selectively permeable to K+ were identified. One of these currents had a unitary conductance of similar to 47 pS and showed a strong inward rectification with symmetric K+ concentrations across the membrane. This K+ current was inhibited by ATP in a concentration-dependent manner with an IC50 (half-inhibition of channel activity) of similar to 130 mu M. Channel activity also was suppressed by ADP, nonhydrolyzable ATP analogue AMP-PNP, and sulfonylurea receptor/channel blocker glibenclamide. The second K+ current had a unitary conductance of similar to 200 pS and showed a weak inward rectification. Similarly, this current was inhibited by ATP (IC50 = 350 mu M), AMP-PNP, and glibenclamide. Unlike the small-conductance ATP-inhibitable K+ channel (S-K-ATP), activation of this large-conductance K+ channel (L-K-ATP) required the presence of micromolar concentration of Ca2+ in the internal solution, but charybdotoxin did not inhibit this channel. The third K+ current was also Ca2+ dependent and had a large conductance (similar to 280 pS). It was inhibited by external charybdotoxin, iberiotoxin, and tetraethylammonium. In contrast to the other two K-ATP channels, ATP enhanced channel open-state probability and unitary conductance, and glibenclamide at concentration of 10-20 mu M had no inhibitory effect on this current. K+ channels that have single-channel and pharmacological properties similar to these three human ATP-modulated KC channels also were observed in experiments on rat neocortical neurons. These results therefore indicate that K-ATP channels are expressed in human neocortical neurons, and two distinct K-ATP channels (S-K-ATP and L-K-ATP exist in the human and rat neurons. The observation that ATP at different concentrations modulates different K+ channels suggests that metabolic rate may be continuously sensed in neurons with resulting alterations in neuronal membrane excitability.