Activation of the Rat P2X7 Receptor by Functionally Different ATP Activation Sites
The homotrimeric P2X7 receptor (P2X7R) contains three ATP<sup>4−</sup> binding sites in its ectodomain. Here, we investigated the role of individual ATP<sup>4−</sup> activation sites in rat P2X7R (rP2X7R) using trimeric concatemers consisting of either three wild-type subunit...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-06-01
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| Series: | Cells |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2073-4409/14/12/855 |
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| Summary: | The homotrimeric P2X7 receptor (P2X7R) contains three ATP<sup>4−</sup> binding sites in its ectodomain. Here, we investigated the role of individual ATP<sup>4−</sup> activation sites in rat P2X7R (rP2X7R) using trimeric concatemers consisting of either three wild-type subunits (7-7-7) or one to three subunits with ATP binding sites knocked out by the K64A mutation. Following expression in <i>Xenopus laevis</i> oocytes, ATP<sup>4−</sup>-elicited ion currents were recorded using the two-microelectrode voltage clamp technique. The 7-7-7 concatamer exhibited a biphasic ATP<sup>4−</sup> concentration dependence, best fit by the sum of two Hill functions, confirming the existence of functionally distinct ATP<sup>4−</sup> activation sites. The activation time course of the 7-7-7 was best approximated by the sum of a fast and a slow exponential saturating activation component. Similarly, deactivation exhibited both fast and slow exponential decay. Only one Hill function was required to best fit the ATP<sup>4−</sup> concentration dependence of concatamers with only two or one ATP<sup>4−</sup> binding sites, and their deactivation time courses largely lacked the slowly deactivating components. We conclude that the binding of one ATP<sup>4−</sup> is sufficient for partial activation of the rP2X7R and that allosteric effects occur when all three ATP<sup>4−</sup> binding sites are occupied, leading to distinct functional activation sites. |
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| ISSN: | 2073-4409 |