PHARMACOLOGICAL AND HISTOCHEMICAL EVIDENCE FOR P2X RECEPTORS IN HUMANUMBILICAL VESSELS

The presence of P2X purinoceptors in human umbilical vessels were stud ied with organ bath recording, radioligand binding assays, autoradiogr aphy, and immunohistochemistry. In isolated umbilical arteries and vei ns from normal term pregnancy, both ATP and alpha,beta-methylene ATP c aused concentration-dependent contractions. ATP-induced responses were blocked by desensitisation with alpha,beta-methylene ATP. However, bo th the ATP- and alpha,beta-methylene ATP-induced responses were not an tagonised by suramin. No significant difference in responses was obser ved in the vessels with or without endothelial cells. Radioligand bind ing assays using [H-3]alpha,beta-methylene ATP showed the presence of a population of high-affinity binding sites in both the arteries and v eins. The K-d values of the binding sites were 2.77 +/- 1.10 nM for th e arteries, and 3.23 +/- 1.22 nM for the veins. The maximum binding si te densities were 634 +/- 237 and 947 +/- 308 fmol/mg protein for the arteries and the veins, respectively. Autoradiographic localisation wi th [H-3]alpha,beta-methylene ATP demonstrated that the specific bindin g sites were only distributed over the smooth muscle cells of the vess els. Immunohistochemical studies with specific polyclonal antibodies a gainst P2X(1-6) receptors showed that positive immunostaining was also restricted to smooth muscle cells. Antibodies against P2X(1) receptor s produced the strongest signals, while antibodies against the other f ive P2X subtypes produced much weaker signals. The results in the pres ent study indicate the existence of P2X purinoceptors in the smooth mu scle of human umbilical vessels. Their physiological functions remain to be studied. (C) 1998 Elsevier Science B.V. All rights reserved.