Submandibular Gland Acinar Cells Express Multiple α1-Adrenoceptor Subtypes

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Abstract
We evaluated an acinar cell line (SMG-C10) cloned from rat submandibular glands as a possible model for α1-adrenoceptor regulation of submandibular function. α1-Adrenoceptors are subdivided into three subtypes called α1A, α1B, and α1D, which can be distinguished from one another by their differential affinity values for subtype-selective α1-adrenoceptor antagonists. Thus, α1-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 α1A-, α1B-, and α1D-adrenoceptors in SMG-C10 cells and submandibular glands. The inhibition of [3H]prazosin binding by 5-methylurapidil (α1A-selective) was biphasic and fit best to a two-site binding model with 40 ± 8% high (KiH)- and 60 ± 10% low (KiL)-affinity binding sites in SMG-C10 cells, and 76% high- and 24% low-affinity binding sites in submandibular glands. Respective KiH and KiL 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 (α1D-selective)] bound with low affinity in SMG-C10 cells and submandibular glands with Ki values of 81 ± 20 and 110 ± 20 nM, respectively. Chloroethylclondine, an irreversible alkylating agent selective for α1B 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 α1A- and α1B-adrenoceptor subtypes, establishing SMG-C10 cells as a potential model for α1-adrenoceptor-mediated secretion.