Effects of a phorbol ester and diacyglycerols on secretion of mucin and arginine esterase by rat submandibular gland cells

The effects of a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) and a diacylglyceride, 1-oleoyl-2-acetyl-glycerol (OAG) on the secretion of two major exocrine products by dispersed rat submandibular cells were investigated. TPA stimulated the release of acinar cell mucin and ductal cell protease (arginine esterase) in a dose- and time-dependent manner. Mucin secretion was also provoked by OAG, which, however, had no effect on arginine esterase release. The unsaturated diacylglycerol, 1,2-diolein, elicited a greater mucosecretory response than did OAG at the same concentration, while the saturated 1,2-distearin produced a smaller response.Mucin and enzyme secretion caused by TPA or OAG in the rat submandibular model was not inhibited by either of two putative antagonists, the antipsychotic drug, fluphenazine, and the antibiotic, polymyxin B.The involvement of extracellular Ca²⁺ in TPA-induced secretion was examined by comparing responses of cells maintained in normal or Ca²⁺-free medium, or in medium containing the ionophore A23187. Although extracellular Ca²⁺ was not an absolute requirement for a secretory response, the results indicate a synergistic relationship between TPA and Ca²⁺ in stimulating the release of both mucin and arginine esterase.These results suggest a role for the Ca²⁺-, phospholipid-dependent enzyme, protein kinase C in the secretory mechanism of mucous and serous cells in the submandibular gland. This is consistent with the proposal that receptor-mediated hydrolysis of membrane phosphoinositides is an initial event in stimulus-response coupling in exocrine cells.