title: Autocrine activation of P2Y1 receptors couples Ca (2+) influx to Ca (2+) release in human pancreatic beta cells.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  We examined the effects of purinergic agonists and antagonists on membrane potential, membrane currents, intracellular Ca(2+) ([Ca(2+)]i) and insulin secretion in human beta cells.
  
  
  RESULTS
  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 [Ca(2+)]i by stimulating Ca(2+) influx and evoking Ca(2+) release via InsP3-receptors in the endoplasmic reticulum (ER). ATP-evoked Ca(2+) 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 [Ca(2+)]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 [Ca(2+)]i and exocytosis without affecting Ca(2+) influx.
  
  
  CONCLUSIONS
  These data demonstrate that ATP acts as a positive autocrine signal in human beta cells by activating P2Y1 receptors, stimulating electrical activity and coupling Ca(2+) influx to Ca(2+) release from ER stores.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, AB, Canada.
authors.forename: Shara
authors.initials: S
authors.lastname: Khan
authors.forename: Richard
authors.initials: R
authors.lastname: Yan-Do
authors.forename: Eric
authors.initials: E
authors.lastname: Duong
authors.forename: Xichen
authors.initials: X
authors.lastname: Wu
authors.forename: Austin
authors.initials: A
authors.lastname: Bautista
authors.forename: Stephen
authors.initials: S
authors.lastname: Cheley
authors.forename: Patrick E
authors.initials: PE
authors.lastname: MacDonald
authors.forename: Matthias
authors.initials: M
authors.lastname: Braun
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D058472:Receptors, Purinergic P2Y1 / Q000378:metabolism*
chemical_list: C465253:2-chloro-N6-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate; D058472:Receptors, Purinergic P2Y1; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium