title: Receptor-independent effects of 2'(3')-O-(4-benzoylbenzoyl)ATP triethylammonium salt on cytosolic pH.
abstract: The effect of the relatively potent P2X7 receptor agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate triethylammonium salt (BzATP-TEA) on cytosolic pH (pHi) was studied using MC3T3-E1 osteoblast-like cells, which endogenously express P2X7 receptors. pHi was measured fluorimetrically using the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. BzATP-TEA (0.3-1.5 mM) elicited fast-onset alkalinization responses. In contrast, adenosine 5'-triphosphate disodium salt (5 mM) failed to reproduce the BzATP-TEA-induced responses, indicating a P2 receptor-independent mechanism. We speculated that triethylamine, which is present in solutions of BzATP-TEA, permeates the plasma membrane, and is protonated intracellularly, leading to an increase in pHi. Consistent with this hypothesis, triethylammonium (TEA) chloride mimicked the effects of BzATP-TEA on pHi. Moreover, measurements using a Cytosensor microphysiometer revealed that TEA chloride transiently suppressed proton efflux from cells, whereas washout of TEA transiently enhanced proton efflux. BzATP-TEA also elicited a sustained increase in proton efflux that was blocked specifically by the P2X7 antagonist A-438079. Taken together, we conclude that BzATP-TEA-induced alkalinization is unrelated to P2X7 activation, but is due to the presence of TEA. This effect may confound assessment of the outcomes of P2X7 activation by BzATP-TEA in other systems. Thus, control experiments using TEA chloride are recommended to distinguish between receptor-mediated and nonspecific effects of this widely used agonist. We performed such a control and confirmed that BzATP-TEA, but not TEA chloride, caused the elevation of cytosolic free Ca(2+) in MC3T3-E1 cells, ruling out the possibility that receptor-independent effects on pHi underlie BzATP-TEA-induced Ca(2+) signaling.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A 5C1, Canada.
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Reyes
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Grol
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Sims
authors.forename: S Jeffrey
authors.initials: SJ
authors.lastname: Dixon
mesh_terms: D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D003600:Cytosol / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D011522:Protons; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism*
chemical_list: D011522:Protons; D058911:Purinergic P2X Receptor Agonists; D000644:Quaternary Ammonium Compounds; D058486:Receptors, Purinergic P2X7; C066585:triethylammonium cation; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate