Fig. 1.

Potential effects of renal ectonucleotidases and consequences for activation of purinoceptor subtypes. The major enzymes involved in each degradative pathway are shown in bold print; for more detail, see text. The information given in the figure indicates the relative potencies of ATP and ADP with respect to P2X and P2Y receptor subtypes. At sufficiently high concentrations, ATP can activate all P2 receptors other than P2Y₆ and P2Y₁₄. It is important to note that nucleotides derived from other bases are also hydrolysed/synthesised by these enzymes, but have been omitted for clarity. Uracil-based nucleotides are particularly significant: UTP is a potent agonist of P2Y₂ and P2Y₄ subtypes, and its dinucleotide derivative UDP is the major naturally occurring agonist of the P2Y₆ subtype. The mechanism(s) of ATP exit from renal cells has/have not been defined (see article by Leipziger [7] in this Special Issue). NDP, nucleoside diphosphate; NTP, nucleoside triphosphate