Autoradiographic localization of transported neutral amino acids in epithelia of cat submandibular and sublingual salivary glands

Abstract

Light-microscopic autoradiography was used to localize the cellular sites for neutral amino acid uptake in submandibular and sublingual salivary gland epithelia. The vasculature of isolated glands was perfused for 3-5 min with either L-(3-3H)serine or L-(4-3H)phenylalanine and then fixed by perfusion with buffered glutaraldehyde. In the submandibular gland the small neutral amino acid L-serine and the aromatic amino acid L-phenylalanine were localized to central acinar cells, demilunar cells and ductal cells. In the sublingual gland silver grains associated with each of these tritiated amino acids were localized to central acinar and ductal cells. Perfusion of both submandibular and sublingual glands with unlabelled L-serine (25 mM) or L-phenylalanine (30 mM) resulted in a significant decrease in the silver grain density associated with each labelled amino acid. The absence of silver grains in the lumina of acinar and ductal cells and the presence of tight junctions near the apical surface of the epithelium strongly suggest that the initial uptake of these amino acids was mediated by basolateral plasma membrane carriers.

Regulation of Amino Acid Influx and Efflux at the Basolateral Plasma Membrane of the Salivary Gland Epithelium: Effects of Parasympathetic Nerve Stimulation

“…It appears that the vasodilatation accompanying parasympathetic nerve stimulation increases amino acid influx at the basolateral membrane without enhancing either D-mannitol or amino acid transfer into the salivary secretion (Table 2). By complementing our rapid membrane transport studies with light microscopic autoradiography, it has now for the first time become possible to identify the actual cellular sites of amino acid uptake (Mann et al, 1986). Our experimental findings provide the basis for studying the hormonal regulation of epithelial membrane transport and protein synthesis in intact secreting or non-secreting salivary glands.…”