Abstract
Specific binding of 3H-PGE1 to plasma membranes prepared from normal human hepatic tissue in the presence of Mg2+ reached saturation at concentrations greater than 50 nM, and could be displaced in the rank-order PGE1 greater than PGE2 greater than PGI2 greater than PGD2 greater than PGF2 alpha at 4 degrees C. Plasma membranes prepared from normal human hepatic tissue showed a high-affinity 3H-PGE1-binding capacity of 51.3 +/- 19.2 fmol mg-1 plasma membrane protein with an equilibrium dissociation constant of 3.8 +/- 1.9 nM, and a low-affinity 3H-PGE1-binding capacity of 104.2 +/- 17.3 fmol mg-1 protein with an equilibrium dissociation constant of 13.9 +/- 2.7 nM. Plasma membranes prepared from hepatocellular cancer tissue revealed a single class of binding sites with an apparent binding capacity of 38.4 +/- 17.3 fmol mg-1 plasma membrane protein (P less than 0.05) and an equilibrium dissociation constant of 12.1 +/- 2.8 nM. Competition studies on plasma membranes prepared from hepatocellular cancer tissue indicated no significant difference in the affinity of various prostaglandins to the receptor proteins as compared to normal hepatic tissue. It is assumed that the decreased 3H-PGE1-binding capacity found in human hepatocellular cancer tissue may reflect an alteration of the receptor protein content of the hepatocytes during carcinogenesis.