Casas-Pruneda Griselda, Reyes Juan Pablo, Pérez-Flores Gabriela, Pérez-Cornejo Patricia, Arreola Jorge
School of Medicine, Universidad Autónoma de San Luis Potosí, San Luis Potosí, SLP, México.
J Physiol. 2009 Jun 15;587(Pt 12):2887-901. doi: 10.1113/jphysiol.2008.167395. Epub 2009 Apr 29.
Mouse parotid acinar cells express P2X4 and P2X7 receptors (mP2X4R and mP2X7R) whose physiological function remains undetermined. Here we show that mP2X4R expressed in HEK-293 cells do not allow the passage of tetraethylammonium (TEA+) and promote little, if any, ethidium bromide (EtBr) uptake when stimulated with ATP or BzATP. In contrast, mP2X7R generates slowly decaying TEA+ current, sustained Na+ current and promotes robust EtBr uptake. However, ATP-activated TEA+ current from acinar cells was unlike that generated by mP2X7R or mP2X4R. Functional interactions between mP2X4R and mP2X7R were investigated in HEK cells co-transfected with different mP2X4 : mP2X7 cDNA ratios and using solutions containing either TEA+ or Na+ ions. Co-expressed channels generated a TEA+ current that displayed faster decay during ATP stimulation than mP2X7R alone. Moreover, cells transfected with a 2 : 1 cDNA ratio displayed decaying kinetics similar to those observed in acinar cells. Concentration-response curves in Na+-containing solutions were constructed for heterologously expressed mP2X4R, mP2X7R and mP2X4R:mP2X7R co-expressions as well as acinar cells. The EC50 values determined were 11, 220, 434 and 442 microM, respectively. Na+ currents generated by expressing mP2X4R or mP2X7R alone were potentiated by ivermectin (IVM). In contrast, IVM potentiation in acinar cells and HEK cells co-expressing P2X4 and P2X7 (1 : 1 or 2 : 1 cDNA ratios) was seen only when the ATP concentration was lowered from 5 to 0.03 mM. Taken together our observations indicate a functional interaction between murine P2X7 and P2X4 receptors. Such interaction might occur in acinar cells to shape the response to extracellular ATP in salivary epithelia.
小鼠腮腺腺泡细胞表达P2X4和P2X7受体（mP2X4R和mP2X7R），其生理功能尚不清楚。在此我们表明，在HEK-293细胞中表达的mP2X4R不允许四乙铵（TEA+）通过，并且在用ATP或BzATP刺激时，几乎不促进溴化乙锭（EtBr）摄取（如果有促进作用的话）。相反，mP2X7R产生缓慢衰减的TEA+电流、持续的Na+电流，并促进大量的EtBr摄取。然而，腺泡细胞中ATP激活的TEA+电流与mP2X7R或mP2X4R产生的电流不同。在以不同的mP2X4:mP2X7 cDNA比例共转染的HEK细胞中，并使用含有TEA+或Na+离子的溶液，研究了mP2X4R和mP2X7R之间的功能相互作用。共表达的通道在ATP刺激期间产生的TEA+电流比单独的mP2X7R表现出更快的衰减。此外，以2:1 cDNA比例转染的细胞显示出与在腺泡细胞中观察到的类似的衰减动力学。针对异源表达的mP2X4R、mP2X7R和mP2X4R:mP2X7R共表达以及腺泡细胞，构建了含Na+溶液中的浓度-反应曲线。测定的EC50值分别为11、220、434和442 microM。单独表达mP2X4R或mP2X7R产生的Na+电流被伊维菌素（IVM）增强。相反，仅当ATP浓度从5 mM降至0.03 mM时，在共表达P2X4和P2X7（1:1或2:1 cDNA比例）的腺泡细胞和HEK细胞中才观察到IVM增强作用。我们的观察结果表明，小鼠P2X7和P2X4受体之间存在功能相互作用。这种相互作用可能发生在腺泡细胞中，以塑造唾液上皮细胞对细胞外ATP的反应。
