Pharmacological characterization of an 18-kDa protein associated with the peripheral-type benzodiazepine receptor in salivary glands

Pharmacological characterization of peripheral type benzodiazepine receptors in rat, rabbit, mouse and human salivary glands was determined by receptor binding and photoaffinity labeling analysis using [H-3]PK14105 (1-(2-fluoro-5-nitrophenyl)-3-isoquinolinecarboxylic acid). [H-3]PK14105 bound to the membranes of salivary glands in rats, rabbits, mice and humans with high affinity at the nanomolar level. The rank order of receptor density in submandibular glands among several species was as follows: human greater than or equal to rat greater than or equal to mouse > rabbit. Competitive potency of receptor ligands against [H-3]PK14105 was as follows: PK11195 greater than or equal to Ro5-4864 > diazepam > clonazepam > Ro15-1788. The rank order of potency against calcium channel ligands and cotransport inhibitors was as follows: nitrendipine > BAY K 8644 > bumetanide > furosemide. Pretreatment with nitrendipine or BAY K 8644 decreased the affinity of [H-3]PK14105 binding to rat parotid gland membranes, without changing the density. The photoaffinity labeling with [H-3]PK14105 indicated the presence of the 18-kDa protein in all salivary glands of our experiment. The inhibition of photolabeling by some receptor ligands was the same results as the receptor binding assay. In conclusion, the peripheral type benzodiazepine receptors include the 18-kDa protein photolabeled with [H-3]PK14105 in salivary glands of rat, mouse, rabbit and human.