Purinergic receptors involved in the stimulation of insulin and glucagon secretion.

The study of purinergic receptors in the endocrine pancreas is a recent field of investigations. Until recently, ATP has been considered only as an intracellular fuel by most authors. Nevertheless for some years evidence has been obtained that extracellular ATP and/or ADP could act on the B cell membrane to increase insulin secretion. Furthermore it was shown that adenosine could act on the A cell surface to increase glucagon secretion. In both cases the involvement of purinoceptors could be demonstrated using structural analogues which are metabolically stable and not taken up by cells. Also the effects of activators of purinoceptors on B and A cells were suppressed by antagonists. So, it was possible to establish that the purinoceptors involved in the stimulation of insulin and glucagon secretion were different. The B cell is endowed with P2 purinoceptors (for ATP and/or ADP) and the A cell possess P1 purinoceptors (for adenosine). It is of interest to note that B and A cells, which secrete hormones with opposite roles, anabolic and catabolic respectively, have two different types of purinoceptors involved in stimulatory process. The purinergic modulation of B and A cells appears to be of physiological relevance.