The first transmembrane domain of the P2X receptor subunit participates inthe agonist-induced gating of the channel

Based on pharmacological properties, the P2X receptor family can be subdivi ded into those homo-oligomers that are sensitive to the ATP analog alpha be ta -methylene ATP(alpha beta meATP) (P2X(1) and P2X(3)) and those that are not (P2X(2), P2X(4), P2X(5), P2X(6), and P2X(7)). We exploited this dichoto my through the construction of chimeric receptors and site-directed mutagen esis in order to identify domains responsible for these differences in the abilities of extracellular agonists to gate P2X receptors. Replacement of t he extracellular domain of the alpha beta meATP-sensitive rat P2X(1) subuni t with that of the alpha beta meATP-insensitive rat P2X2 subunit resulted i n a receptor that was still alpha beta meATP-sensitive, suggesting a non-ex tracellular domain was responsible for the differential gating of P2X recep tors by various agonists. Replacement of the first transmembrane domain of the rat P2X2 subunit with one from an alpha beta meATP-sensitive subunit (e ither rat P2X(1) or P2X3 subunit) converted the resulting chimera to alpha beta meATP sensitivity. This conversion did not occur when the first transm embrane domain came from a non-alpha beta meATP-sensitive subunit. Site-dir ected mutagenesis indicated that the C-terminal portion of the first transm embrane domain was important in determining the agonist selectivity of chan nel gating for these chimeras. These results suggest that the first transme mbrane domain plays an important role in the agonist operation of the P2X r eceptor.