Species- and agonist-dependent differences in the deactivation-kinetics of P2X7 receptors.

In this study we have expressed recombinant P2X7 receptors in HEK293 cells and examined the reasons for the species- and agonist-dependent differences in the time taken for the closure of the P2X7 receptor ion-channels after agonist removal. Channel closure times, measured in electrophysiological studies or by measuring cellular permeability to ethidium cations, were slower at rat than at human or mouse P2X7 channels following washout of the P2X7 agonist 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP). In contrast, there were no species differences in channel closure times when ATP was the agonist.

Complexities of measuring antagonist potency at P2X(7) receptor orthologs.

The ability of P2 antagonists to affect agonist-stimulated fluorescent dye accumulation in cells expressing human, rat, or mouse P2X(7) receptors was examined. Several compounds, including pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), which was previously thought to be a weak P2X(7) receptor antagonist, possessed high potency (nanomolar IC(50)) at human and rat P2X(7) receptors. However, there were species differences in antagonist potency with PPADS, pyridoxal 5'-phosphate (P5P), and periodate-oxidized ATP (OxATP) exhibiting 20- to 500-fold higher potency for human than for mouse P2X(7) receptors.

Apparent species differences in the kinetic properties of P2X(7) receptors.

1. Apparent species differences in the responses of recombinant P2X(7) receptors to repeated application of 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) have been investigated. 2.

Identification and characterization of an endogenous P2X7 (P2Z) receptor in CHO-K1 cells.

CHO-K1 cells were examined for their cellular responses to the P2 receptor agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (DbATP), and for the presence of mRNA for P2X receptors. Reverse transcriptase-polymerase chain reactions, using primers directed against the rat P2X subunits, detected the presence of P2X7 but not P2X1-P2X6 subunits. DbATP (EC50 approximately equal to 100 microM) evoked non-desensitizing inward currents which reversed at approximately equal to 0 mV, suggesting activation of a non-selective cation channel.