Figure 2.

Desensitization of P2X₁/P2X₂ chimeras distinguishes three domains. (A) Representative currents evoked by 10-s applications of ATP (100 μM) to oocytes expressing five different chimeric receptors. (B) Schematic representation of the three domain chimeras: grey, P2X₁; black, P2X₂. Rectangles indicate positions of putative membrane-spanning regions M1 and M2. Top four rows show P2X₁ and substitutions of P2X₂ segments into P2X₁: N-domain (chimera 1), C-domain (chimera 2), and N- and C-domains (chimera 3). Bottom four rows show P2X₂ receptor and substitutions of P2X₁ segments into P2X₂: N-domain (chimera 4), C-domain (chimera 5), and N- and C-domains (chimera 6). Mean currents in P2X₁, chimeras 1-3, P2X₂, and chimeras 4-6 were (measured in nA, number of oocytes in parentheses) 1600 ± 160 (38), 545 ± 82 (19), zero, 824 ± 250 (7), 3150 ± 260 (47), 1340 ± 260 (6), 1390 ± 239 (12), and 2310 ± 210 (14), respectively.