THE EFFECTS OF NUCLEOTIDES AND POTASSIUM CHANNEL OPENERS ON THE SUR2AKIR6.2 COMPLEX K+ CHANNEL EXPRESSED IN A MAMMALIAN-CELL LINE, HEK293TCELLS/

The effects of potassium channel opening drugs and intracellular nucle otides on the ATP-sensitive K+ (K-ATP) channel composed of SUR2A and K ir6.2 in HEK293T cells were examined using the patch-clamp technique. The SUR2A/Kir6.2 channel was activated effectively by pinacidil, margi nally by nicorandil but not by diazoxide. The pinacidil-activated chan nel currents were inhibited by glibenclamide with a K-i value of 160 n M. Upon formation of inside-out (I-O) patches, spontaneous openings of the channels appeared, which were inhibited by intracellular ATP (ATP (i)) equipotently in the presence and in the absence of intracellular Mg2+ (Mg-i(2+)). The channel activity ran-down gradually in I-O patche s. The run-down channels could be reactivated by ATP(i) only in the pr esence of Mg-i(2+). Uridine 5'-diphosphate (UDP) antagonized the ATP(i )-mediated inhibition of the channel activity before run-down. After r un-down, UDP activated the channel without antagonizing ATP(i)-mediate d channel inhibition. Thus, the SUR2A/Kir6.2 reproduced the major prop erties of the native cardiac K-ATP channel well in terms of nucleotide regulation and pharmacology, and therefore can be a useful tool with which to elucidate the molecular mechanisms characterizing the K-ATP c hannel.