Mapping subcellular distribution of Na+-K+-ATPase in rat parotid gland

Abstract

Recent subcellular fractionation studies have raised the possibility that Na+-K+-ATPase might be present in both the apical and the basal-lateral membranes of exocrine gland acinar cells. Analytical fractionation and immunofluorescence microscopy studies of rat parotid glands were performed to confirm this interpretation. The distributions of biochemical markers after analyses based on differential sedimentation, equilibrium density-gradient centrifugation, and partitioning in an aqueous polymer two-phase system defined a total of 15 physically and biochemically distinct membrane populations. Among these populations, it was possible to select one (designated population i) with the characteristics expected of acinar cell basal-lateral plasma membranes. It contained Na+-K+-ATPase enriched 33-fold, and gamma-glutamyl transpeptidase enriched 23-fold with respect to the initial homogenate. A second population (designated population c) had the characteristics expected of acinar cell apical plasma membranes; it contained Na+-K+-ATPase enriched 28-fold, and gamma-glutamyl transpeptidase enriched 53-fold with respect to the initial homogenate. Although the identification of population c remains provisional, immunofluorescence studies verified that Na+-K+-ATPase is present in both the apical and the basal-lateral acinar cell plasma membranes. In view of these results, it is likely that the apical Na+-K+-ATPase would participate in series with basal-lateral sodium- and chloride-entry pathways in driving the secretory electrolyte fluxes.

Acute and chronic regulation of Na+/K+-ATPase transport activity in the RN22 Schwann cell line in response to stimulation of cyclic AMP production

“…In contrast to the regulatory mechanism responsible for the acute stimulation of Na ϩ /K ϩ -ATPase transport activity, our results suggest that a separate mechanism, i.e., transporter protein translocation from an intracellular storage pool to the plasma membrane, is involved in the delayed chronic stimulation of the Na ϩ /K ϩ -ATPase transport activity (Ariyasu et al, 1985;Conteas et al, 1986;Omatsu-Kanbe and Kitasato, 1990;Yiu et al, 1988). A direct contribution of Na ϩ ,K ϩ ,2Cl Ϫ -cotransport to chronic stimulation of Na ϩ / K ϩ -ATPase transport activity was ruled out by 2 experimental results.…”

Cellular Mechanisms Underlying the Production of Primary Secretory Fluid in Salivary Glands

“…Studies with antibodies to rat kidney Na, K-ATPase suggested the presence in rat parotid of two distinct membrane populations enriched in enzyme activity. 9 These populations had the characteristics expected of basolateral and apical plasma membranes of acinar cells. 9 Another study using monoclonal antibodies to the P-subunit of canine Na, KATPase demonstrated relatively low levels of enzyme activity in dog parotid acinar cells, 70 but the activity was confined to the basolateral cell membrane and no activity was ascertained in apical membranes.…”

An Overview of Autonomic Regulation of Parotid Gland Activity: Influence of Orchiectomy

“…Na + -K + -ATPase is found in the parotid gland along the apical and basolateral plasma membranes of acinar, striated and excretory duct cells. The apical Na + -K + -ATPase is proposed to participate in series with basolateral sodium and chloride entry pathways in driving secretory electrolyte fluxes [Speight and Chisholm, 1984;Conteas et al, 1986;Simson and Chao, 1994]. Furthermore, it is suggested that in acinar cells Na + is not only transported paracellularly but is also actively transported intracellularly into the luminal space by the Na + -K + -ATPase lo- cated on luminal plasma membranes.…”