Handling of calcium by the ferret submandibular gland

Extracellular Ca(2+) sensing in salivary ductal cells

Ca(2+) is secreted from the salivary acinar cells as an ionic constituent of primary saliva. Ions such as Na(+) and Cl(-) get reabsorbed whereas primary saliva flows through the salivary ductal system. Although earlier studies have shown that salivary [Ca(2+)] decreases as it flows down the ductal tree into the oral cavity, ductal reabsorption of Ca(2+) remains enigmatic. Here we report a potential role for the G protein-coupled receptor, calcium-sensing receptor (CSR), in the regulation of Ca(2+) reabsorption by salivary gland ducts. Our data show that CSR is present in the apical region of ductal cells where it is co-localized with transient receptor potential canonical 3 (TRPC3). CSR is activated in isolated salivary gland ducts as well as a ductal cell line (SMIE) by altering extracellular [Ca(2+)] or by aromatic amino acid, L-phenylalanine (L-Phe, endogenous component of saliva), as well as neomycin. CSR activation leads to Ca(2+) influx that, in polarized cells grown on a filter support, is initiated in the luminal region. We show that TRPC3 contributes to Ca(2+) entry triggered by CSR activation. Further, stimulation of CSR in SMIE cells enhances the CSR-TRPC3 association as well as surface expression of TRPC3. Together our findings suggest that CSR could serve as a Ca(2+) sensor in the luminal membrane of salivary gland ducts and regulate reabsorption of [Ca(2+)] from the saliva via TRPC3, thus contributing to maintenance of salivary [Ca(2+)]. CSR could therefore be a potentially important protective mechanism against formation of salivary gland stones (sialolithiasis) and infection (sialoadenitis).

Histological and histochemical observations on salivary microliths in ferret

The fortuitous observation of salivary microliths in ferret was pursued in the present investigation. Major salivary glands obtained post-mortem from mature ferrets of either sex were examined with the use of histology and light microscopical histochemistry for calcium, protein, amino acids, mucosubstances and hydrolytic enzymes. Microliths were detected in most parotids, but were absent from submandibular and sublingual glands. The microliths were usually seen in lumens, and occasionally in parenchyma and interstices. They were variably stained for calcium, tryptophan, and neutral and acidic mucosubstances, similarly to acinar or ductal secretory granules. Unlike secretory granules, microliths showed autofluorescence, high levels of tyrosine and a low concentration of -SS- groups. Acid phosphatase and beta-glucuronidase reaction surrounded non-luminal microliths. The present data establish ferret as a new model for the investigation of salivary microliths and do not support the notion of microliths being almost absent from the parotid. Probably there is secretory inactivity in ferret parotid and this fosters the formation and accumulation of microliths containing calcium and disintegrated secretory material.

Innervation and myoepithelial arrangements in the submandibular salivary gland of ferret investigated by enzyme, catecholamine and filament histochemistry

Although the submandibular gland of ferret is useful for studying salivary secretory processes which are regulated by nerves and involve myoepithelial activity, little attention has been paid to its parenchymal innervation and myoepithelial arrangements. Therefore, glands obtained postmortem from mature ferrets of both sexes were here examined with the use of light-microscopic histochemical techniques for cholinesterases, phosphatases and phosphorylase, histofluorescence for catecholamines, and milling dyes. Acetylcholinesterase staining was associated with nerve trunks in the interlobular stroma and an extensive intralobular network of nerve fibres, presumably of a cholinergic type, embracing acini and ducts. There were fewer fibres containing fluorescing catecholamines, presumably adrenergic. They were largely associated with acini. Numerous stellate cells with fine branching processes embracing acini, presumably myoepithelial cells, and a few spindle-shaped basal cells, investing striated ducts, were demonstrated on frozen tissue by alkaline phosphatase, but not by adenosine triphosphatase, inosine diphosphatase and phosphorylase. Cells of similar shape and distribution were also demonstrated by staining with milling dyes on fixed tissues, indicating possibly a filamentous constituent conferring mechanical stability and/or contractile ability. Together, these results suggest, firstly, that a cholinergic-type parenchymal innervation is prominent in the submandibular gland of ferret, although many adrenergic nerves are also present, and, secondly that the gland has a very extensive myoepithelial network which is possibly involved in membrane transport, and the support and or contraction of the secretory parenchyma.

Morphological phenotypes and functional capabilities of submandibular parenchymal cells of the ferret investigated by protein, mucosubstance and enzyme histochemistry

Submandibular glands obtained post-mortem from mature ferrets of both sexes were examined with the use of light microscopical histochemical methods for proteins, mucosubstances and enzymes associated with cell functions or organelles. Demilunar cells showed carboxylated mucosubstances that were mainly non-sulphated, and diffuse activity for peroxidase, E600-sensitive esterase and acid phosphatase. Thiol groups were also detected in these cells. Central acinar cells showed sulphated mucosubstances, disulphides and reticular staining for thiamine pyrophosphatase. Intercalary ducts showed diffuse activity for NADH and NAD(P)H dehydrogenases. Striated ducts contained protein, tryptophan, disulphides, neutral mucosubstances and E600-sensitive esterase periluminally. Basally, the striated ductal cells showed variable activity for peroxidase, cytochrome oxidase, succinate dehydrogenase and acid phosphatase. Basolateral plasma membranes of these cells exhibited ouabain-sensitive Na,K-ATPase activity. The collecting ducts were characterized by variable periluminal staining for acid phosphatase, beta-glucuronidase, acid beta-galactosidase and E600-resistant esterase. The results suggest that the histological appearances of the acini of the submandibular gland of the ferret are dependent on the synthesis of secretory acid glycoproteins, that the striated ducts are involved with the secretion of tryptophan-rich product comprising neutral glycoproteins and showing esterase activity and with marked transport of ions and that the collecting ducts are involved with absorption.