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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

Submandibular Gland Acinar Cells Express Multiple ₁-Adrenoceptor Subtypes

Department of Pharmacology, Creighton University School of Medicine, Omaha, Nebraska

We evaluated an acinar cell line (SMG-C10) cloned from rat submandibular glands as a possible model for ₁-adrenoceptor regulation of submandibular function. ₁-Adrenoceptors are subdivided into three subtypes called _1A, _1B, and _1D, which can be distinguished from one another by their differential affinity values for subtype-selective ₁-adrenoceptor antagonists. Thus, ₁-adrenoceptor subtypes in SMG-C10 cells were characterized with reverse transcription-polymerase chain reaction (RT-PCR) and [³H]prazosin binding in side-by-side experiments with native submandibular glands. RT-PCR identified mRNAs for _1A-, _1B-, and _1D-adrenoceptors in SMG-C10 cells and submandibular glands. The inhibition of [³H]prazosin binding by 5-methylurapidil (_1A-selective) was biphasic and fit best to a two-site binding model with 40 ± 8% high (K_iH)- and 60 ± 10% low (K_iL)-affinity binding sites in SMG-C10 cells, and 76% high- and 24% low-affinity binding sites in submandibular glands. Respective K_iH and K_iL values for 5-methylurapidil were 1.9 ± 0.4 and 100 ± 30 nM in SMG-C10 cells and 3.2 ± 0.8 and 170 ± 20 nM in submandibular glands. BMY-7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (_1D-selective)] bound with low affinity in SMG-C10 cells and submandibular glands with K_i values of 81 ± 20 and 110 ± 20 nM, respectively. Chloroethylclondine, an irreversible alkylating agent selective for _1B adrenoceptors, reduced the density of [³H]prazosin binding sites by 42 and 26% in SMG-C10 and submandibular membranes, respectively. Thus, SMG-C10 cells and submandibular glands are similar in expressing receptor protein for _1A- and _1B-adrenoceptor subtypes, establishing SMG-C10 cells as a potential model for ₁-adrenoceptor-mediated secretion.

Address correspondence to: Dr. Charles S. Bockman, Department of Pharmacology, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE 68178. E-mail: cbockman{at}creighton.edu

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