The P2X1 receptor belongs to a family of oligomeric ATP-gated ion channels
with intracellular N and C termini and two transmembrane segments separatin
g a large extracellular domain. Here, we describe a naturally occurring dom
inant negative P2X1 mutant. This mutant lacks one leucine within a stretch
of four leucine residues in its second transmembrane domain (TM2) (amino ac
ids 351-354). Confocal microscopy revealed proper plasma membrane localizat
ion of the mutant in stably transfected HEK293 cells. Nevertheless, voltage
-clamped HEK243 cells expressing mutated P2X1 channels failed to develop an
ATP or ADP-induced current. Furthermore, when co-expressed with the wild t
ype receptor in Xenopus oocytes, the mutated protein exhibited a dose-depen
dent dominant negative effect on the normal ATP or ADP-induced P2X1 channel
activity. These data indicate that deletion of a single apolar amino acid
residue at the inner border of the P2X1 TM2 generates a nonfunctional chann
el, The inactive and dominant negative form of the P2X1 receptor may consti
tute a new tool for the study of the physiological role of this channel in
native cells.