Sustained stimulation of vasopressin and oxytocin release by ATP and phenylephrine requires recruitment of desensitization-resistant P2X purinergic receptors

Gomes DA, Song Z, Stevens W, Sladek CD. Sustained stimulation of vasopressin and oxytocin release by ATP and phenylephrine requires recruitment of desensitization-resistant P2X purinergic receptors. Am J Physiol Regul Integr Comp Physiol 297: R940-R949, 2009. First published July 22, 2009; doi: 10.1152/ajpregu.00358.2009.-Coexposure of hypothalamo-neurohypophyseal system explants to ATP and phenylephrine [PE; an alpha 1-adrenergic receptor (alpha 1-AR) agonist] induces an extended elevation in vasopressin and oxytocin (VP/OT) release. New evidence is presented that this extended response is mediated by recruitment of desensitization-resistant ionotropic purinergic receptor subtypes (P2X-Rs): 1) Antagonists of the P2X2/3 and P2X7-Rs truncated the sustained VP/OT release induced by ATP + PE but did not alter the transient response to ATP alone. 2) The P2X2/3 and P2X7-R antagonists did not alter either ATP or ATP + PE-induced increases in [Ca2+](i). 3) P2X2/3 and P2X7-R agonists failed to elevate [Ca2+](i), while ATP-gamma-S, an agonist for P2X2-Rs increased [Ca2+](i) and induced a transient increase in VP/OT release. 4) A P2Y1-R antagonist did not prevent initiation of the synergistic, sustained stimulation of VP/OT release by ATP + PE but did reduce its duration. Thus, the desensitization-resistant P2X2/3 and P2X7-R subtypes are required for the sustained, synergistic hormone response to ATP + PE, while P2X2-Rs are responsible for the initial activation of Ca2+-influx by ATP and ATP stimulation of VP/OT release. Immunohistochemistry, coimmunoprecipitation, and Western blot analysis confirmed the presence of P2X2 and P2X3, P2X2/3, and P2X7-R protein, respectively in SON. These findings support the hypothesis that concurrent activation of P2X2-R and alpha 1-AR induces calcium-driven recruitment of P2X2/3 and 7-Rs, allowing sustained activation of a homeostatic circuit. Recruitment of these receptors may provide sustained release of VP during dehydration and may be important for preventing hemorrhagic and septic shock.