Purinergic Signalling in Pancreatic Islet Endothelial Cells - Extracellular ATP and Adenosine as Regulators of Endothelial Cell Function - page 208

Chapter 12
Purinergic Signalling in Pancreatic Islet
Endothelial Cells

Leif Jansson, Eva Grapengiesser, and Bo Hellman

Abstract Both the microvascular endothelium and the endocrine cells in the
pancreatic islet can release and react upon ATP. In support for the idea that inter-
mittently released ATP, related to exocytosis of insulin secretory granules, affects
the secretory activity of the capillary endothelium, we have demonstrated that iso-
lated endothelial cells respond to activation of P2Y 2 receptors with pronounced and
extended rises of [Ca 2+ ] i . The presence of such ATP effect is consistent with reports
that -cells regulate the blood flow within islets, where adenosine is a key media-

tor, and that the endothelial cell produce pro-angiogenic and angiostatic factors. In
β

β

-cells down-regulation of P2Y 1 receptors results in disappearance of the transients
of [Ca 2+ ] i supposed to entrain these cells into a common rhythm. Since the islet
endothelial cells respond to activation of P2Y 2 receptors with extended elevation of
[Ca 2+ ] i , it is likely that the accompanying release of ATP is prolonged. Accordingly,
the endothelial cells may have a tonic inhibitory action on the coordination of islet
release pulses.

Ca 2+ Keywords Adenosine · Arteriole · ATP · β -cells · oscillations ·

Capillaries · Endothelium · Insulin · Islet blood flow · Pancreas · Pancreatic

islets · Purinergic signaling · P2X receptors · P2Y receptors · UTP

12.1 Introduction

Purines and pyrimidines released to or formed within the extracellular space serve
as signalling molecules in many organs of the body by acting on one or several
ionotropic P2X and metabotropic P2Y receptors [11]. The purinergic receptors

B

L. Jansson ( )

Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Husargatan 3,
Box 571, SE-751 23, Uppsala, Sweden
e-mail: [e-mail]