Autocrine activation of P2Y₁ receptors couples Ca²⁺ influx to Ca²⁺ release in human pancreatic beta cells

There is evidence that ATP acts as an autocrine signal in beta cells but the receptors and pathways involved are incompletely understood. Here we investigate the receptor subtype(s) and mechanism(s) mediating the effects of ATP on human beta cells.

We examined the effects of purinergic agonists and antagonists on membrane potential, membrane currents, intracellular Ca²⁺ ([Ca²⁺]_i) and insulin secretion in human beta cells.

Extracellular application of ATP evoked small inward currents (3.4 ± 0.7 pA) accompanied by depolarisation of the membrane potential (by 14.4 ± 2.4 mV) and stimulation of electrical activity at 6 mmol/l glucose. ATP increased [Ca²⁺]_i by stimulating Ca²⁺ influx and evoking Ca²⁺ release via InsP₃-receptors in the endoplasmic reticulum (ER). ATP-evoked Ca²⁺ release was sufficient to trigger exocytosis in cells voltage-clamped at −70 mV. All effects of ATP were mimicked by the P2Y_(1/12/13) agonist ADP and the P2Y₁ agonist MRS-2365, whereas the P2X_(1/3) agonist α,β-methyleneadenosine-5-triphosphate only had a small effect. The P2Y₁ antagonists MRS-2279 and MRS-2500 hyperpolarised glucose-stimulated beta cells and lowered [Ca²⁺]_i in the absence of exogenously added ATP and inhibited glucose-induced insulin secretion by 35%. In voltage-clamped cells subjected to action potential-like stimulation, MRS-2279 decreased [Ca²⁺]_i and exocytosis without affecting Ca²⁺ influx.

These data demonstrate that ATP acts as a positive autocrine signal in human beta cells by activating P2Y₁ receptors, stimulating electrical activity and coupling Ca²⁺ influx to Ca²⁺ release from ER stores.