• Song Zhilin
• Vijayaraghavan Sukumar
• Sladek Celia D

American journal of physiology. Regulatory, integrative and comparative physiology

• Publish Date: Jul 2006
• ISSN: 0363-6119
• Volume: 291
• Issue: 1
• Pages: R37-45
• Medium: Print
• Language: English
• Citation (JAMA): Song Zhilin, Vijayaraghavan Sukumar, Sladek Celia D, et al. Simultaneous Exposure to Atp and Phenylephrine Induces a Sustained Elevation in the Intracellular Calcium Concentration in Supraoptic Neurons.. Am. J. Physiol. Regul. Integr. Comp. Physiol. Jul 2006;291:R37-45

Abstract

Vasopressin (VP) release from the hypothalamo-neurohypophyseal system (HNS) is stimulated by ATP activation of P2X purinergic receptors and by activation of 1-adrenergic receptors by phenylephrine (PE). These responses are potentiated by simultaneous exposure to ATP+PE. Potentiation was blocked by depleting intracellular calcium stores with thapsigargin. To test the hypothesis that the synergistic response to ATP+PE reflects alterations in the intracellular calcium concentration ([Ca2+]i), [Ca2+]i was monitored in supraoptic neurons in HNS explants loaded with fura 2-AM. Both ATP and PE induced rapid, but transient, elevations in [Ca2+]i. In 0.3 mM Ca2+, the peak response to ATP was greater than to PE but did not differ from the peak response to ATP+PE. A sustained elevation in [Ca2+]i was induced by ATP+PE, that was greater than ATP or PE alone. In 2 mM Ca2+, the peak response to ATP+PE was significantly greater than to either ATP or PE alone, and the sustained response to ATP+PE was greater than to either agent alone. Responses were comparable in the presence of TTX. The sustained elevation in [Ca2+]i was also observed when ATP+PE was removed after 1 min, but it was eliminated by either thapsigargin or removing external calcium, indicating that both calcium influx and calcium release from internal stores are required. Some cells were vasopressinergic based on a VP-induced increase in [Ca2+]i. These observations support the hypothesis that simultaneous exposure to ATP+PE induces a different pattern of [Ca2+]i than either agent alone that may initiate events leading to synergistic stimulation of VP release.

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