Abstract

Purinergic P2X1 and P2X7 receptors are co-expressed in several cell types such as lymphocytes or epithelial cells. Here we examined whether these two P2X subtypes interact with each other in a manner that results in a mutual alteration of their electrophysiologic behaviour. Furthermore, since specific pharmacological tools are needed to assign distinct effects to a particular receptor subtype in native cells, we assessed a series of compounds for their capacity to separate individual current components in cells that co-expressed both receptor subtypes. In Xenopus oocytes, coexpression neither changed the time courses of activation, desensitization and deactivation nor recovery from desensitization when compared to oocytes that express either hP2X1 or hP2X7 receptors alone. A selective activation of hP2X7 receptors was achieved with benzoyl-benzoyl-ATP, which did not activate P2X1 receptor currents. P2X7 receptors could also be selectively activated by ATP when co-applied with 1 μM NF449, a suramin derivative, which is 100,000 fold more potent in blocking P2X1 than P2X7 receptors. ab-methylene-ATP, a reportedly hP2X1 receptor-specific agonist, as well as oxidized-ATP, brilliant blue or KN62, reported hP2X7 receptor antagonists, were found to be ineffective in separating hP2X1 receptor current from the P2X7 current. The best way for a selective activation of the hP2X1 receptor component in cells co-expressing the P2X7 receptor is the application of low concentrations of ATP ( < 1 μM) or the addition of Mg2+ when using higher concentrations of ATP.

Keywords: purinergic receptor, p2x receptor, subtype, oocyte, whole cell current, kinetics, agonist, antagonist