Purinergic Signalling in Pancreatic Islet Endothelial Cells - Extracellular ATP and Adenosine as Regulators of Endothelial Cell Function - page 217

M of ATP, ADP, UTP and UDP on [Ca 2+ ] i in islet endothelial cells and

Fig. 12.4 Effects of 10 μ

β -cells superfused with a medium containing 5 mM glucose. The test substances were added during

5-min periods. Representative for 5 experiments. From [37]

functionally active P2Y 1 receptors. Endothelial cells sometimes express P2X recep-
tors, which mediate vasodilation [64, 79, 85]. Since UTP was equally effective as
ATP in raising [Ca 2+ ] i , it is unlikely that islet endothelial cells have functionally
active P2X receptors.
Evidence has been provided that glucose stimulation of the islet blood flow
involves adenosine P1 receptors [17]. However there was no increase of [Ca 2+ ] i
when islet endothelial cells were exposed to 10

M adenosine. The latter find-
ing supports the idea that the vasodilator action of adenosine involves arterioles
outside the islets rather than the intra-islet capillaries. Acetylcholine is widely
employed for initiating release of endothelial factors regulating the vascular tone
[88]. Nevertheless 10

μ

M acetylcholine elicited [Ca 2+ ] i increase only in the

-cells.
The observation that endothelial cells respond with rise of [Ca 2+ ] i to purinergic,
but not to cholinergic stimuli, is not unique for islet capillaries but is seen also in
brain [44].

μ β