ATP-gated P2X 3 receptors constitute a positive autocrine signal for insulin release in the human pancreatic β cell

Abstract

Extracellular ATP has been proposed as a paracrine signal in rodent islets, but it is unclear what role ATP plays in human islets. We now show the presence of an ATP signaling pathway that enhances the human β cell9s sensitivity and responsiveness to glucose fluctuations. By using in situ hybridization, RT-PCR, immunohistochemistry, and Western blotting as well as recordings of cytoplasmic-free Ca²⁺ concentration, [Ca²⁺]_i, and hormone release in vitro, we show that human β cells express ionotropic ATP receptors of the P2X₃ type and that activation of these receptors by ATP coreleased with insulin amplifies glucose-induced insulin secretion. Released ATP activates P2X₃ receptors in the β-cell plasma membrane, resulting in increased [Ca²⁺]_i and enhanced insulin secretion. Therefore, in human islets, released ATP forms a positive autocrine feedback loop that sensitizes the β cell9s secretory machinery. This may explain how the human pancreatic β cell can respond so effectively to relatively modest changes in glucose concentration under physiological conditions in vivo.