CHARACTERIZATION OF PERIPHERAL-TYPE BENZODIAZEPINE BINDING-SITES FROM RAT AND PIG PANCREAS

The binding of [H-3]1-(2-chlorophenyl-N-methyl-1-methyl-propyl)-3-isoquinolinecarb oxamide ([H-3]PK-11195) and [H-3]7-chloro-1,3-dihydro-1-methyl-5-(p-chlorophenyl)-2H-1,4-benzodiazepin-2-on ([H-3]Ro5-4864) to membrane preparations of pancreas was studied in the rat and pig. [H-3]PK-11195 bound with high affinity to rat and pig membrane preparations yielding maximal numbers of binding sites (B-max) of 2393 +/- 160 and 777 a 65 fmol/mg of protein, respectively, and equilibrium dissociation constant (K-d) values of 3.01 c 0.25 and 3.9 +/- 0.23 nM, respectively. [H-3]Ro5-4864 successfully labelled rat but not pig pancreatic membranes, yielding a Kd value of 6.45 +/- 0.5 nM and a B-max value of 551 +/- 43 fmol/mg of protein. Displacement studies showed a similar rank order of potency of various unlabelled ligands against both [H-3]Ro5-4864 and [H-3]PK-11195 binding to rat and pig membrane preparations (PK-11195 greater than or equal to Ro5-4864 > diazepam > flunitrazepam much greater than flumazenil). These results suggest that [H-3]PK-11195 binds with high affinity and specificity to rat and pig pancreas and [H-3]Ro5-4864 binds with high affinity and specificity to rat but not pig pancreas.