P2X2 purinergic receptors (P2X2R) are responsible for ATP stimulated calcium influx in supraoptic nucleus neurons (SON)

Abstract

ATP and phenylephrine (PE, α1 adrenergic receptor agonist) co‐applied to explants of the hypothalamo‐neurohypophyseal system (HNS) act synergistically to stimulate vasopressin and oxytocin release and generate an extended elevation in intracellular calcium ([Ca++]i) in SON (AJP:Regul 291:R31,'06). The latter may be the driving force for synergism in hormone release. ATP activated both P2X and P2YRs to increase [Ca++]i in SON (AJP:Regul 292:R423, ‘07). Our current studies evaluated the relative contribution of different P2XR subtypes to ATP stimulated Ca++ influx. HNS explants were loaded with the Ca++‐sensitive dye, fura 2AM (100 uM for 10 min., then 20 uM for 50 min in 0.02% pluronic acid), and [Ca++]i in SON was monitored by ratiometric analysis of fluorescence emitted by excitation at 340 and 380 nm. Neither A317491 (300 nM, P2X3 and P2X2/3R antag.) nor BBG (1 uM, P2X7R antag.) attenuated the increase in [Ca++]i induced by ATP or ATP+PE. α,β‐MethyleneATP (100 uM, a P2X3 and P2X2/3R agonist) did not increase [Ca++]i. BzATP increased [Ca++]i at 100 and 200 uM (activates P2X2Rs), but not at 20 uM (activates only P2X7Rs). Moreover, ATP γ S (100 uM, P2X2 and P2X4R agonist) also induced an increase in [Ca++]i. Since P2X4Rs are not sensitive to PPADS, and PPADS (10uM) blocked ATP stimulated Ca++ influx, together these findings support a primary role for P2X2Rs in stimulating Ca++ influx in SON. Since the non‐desensitizing P2X2/3 and P2X7Rs are important for sustained VP release induced by ATP+PE (Gomes et al, EB'08), but do not participate in Ca++ signal generation, ATP+PE synergism in hormone release may require a shift in P2XR subtypes. Supported by NIH R01‐NS27975.