recognized as important extracellular signaling molecules in many biological systems (1). In epithelia, ATP signaling is thought to regulate fluid transport, and exocrine glands are one of the first epithelia where the effect of ATP on ion channels and Ca signaling was observed (2, 3). Nevertheless, many steps in ATP signaling, also known as purinergic signaling, remain to be clarified. This includes the questions of where and how ATP is released, which purinergic receptors are stimulated and where and how ATP is hydrolyzed by ecto-nucleotidases. In general, our studies aim to understand the role of purinergic signaling in communication between pancreatic acini and ducts. We have established that pancreatic acini release ATP and nucleotidases (4, 5) possibly from zymogen granules and we propose that pancreatic ducts are important sites for purinergic signaling, where the effect on specific receptors is translated into epithelial cell responses. Therefore, our recent studies focused on determining expression and effect of purinergic and adenosine receptors and their effect on Ca and Cl transport.