CHARACTERIZATION OF PERIPHERAL-TYPE BENZODIAZEPINE BINDING-SITES FROMRAT AND PIG PANCREAS

The binding of henyl-N-methyl-1-methyl-propyl)-3-isoquinolinecarb oxam ide ([H-3]PK-11195) and ethyl-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, a nd 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 st udies showed a similar rank order of potency of various unlabelled lig ands against both [H-3]Ro5-4864 and [H-3]PK-11195 binding to rat and p ig 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 t o rat and pig pancreas and [H-3]Ro5-4864 binds with high affinity and specificity to rat but not pig pancreas.