Purinergic Regulation of Bile Ductular Secretion
The term purinergic receptor, however, is no longer valid, since it is clear that pyrimidinergic nucleotides, can activate the receptors as well. Hence, the most appropriate name for these receptors may be nucleotide receptors, although the term purinergic receptors remains in common usage. In early experiments, it became evident that distinct receptors were activated by nucleosides, such as Purinergic agonists. Nucleoside receptors became known as P1 receptors, and nucleotide receptors became known as P2 receptors. Aside from the role of extracellular nucleotides in regulation platelet aggregation, perhaps their most interesting role is in control of epithelial secretion. P2Y receptors are expressed widely in epithelia. At least four P2Y receptor subtypes are found in a variety of secretory epithelia, including salivary glands, intestinal epithelia, renal epithelia, pancreatic epithelia, hepatocytes, and respiratory epithelia. Extracellular nucleotides also regulate functions other than chloride secretion in epithelia. In respiratory and intestinal epithelia, activation of P2Y receptors is linked to mucin secretion.