Osteogenesis bioassay and immunohistochemical and radioisotopic studies of parotin, parotid gland extract, and subunit

Bioassay data support the hypothesis that the salivary gland participates in endocrine regulation of the development and maintenance of connective tissues. Epiphyseal cartilages become dystrophic in young growing rats after the resection of all major salivary glands. A subunit obtained from parotin, an extract of bovine parotid glands, contains the active agent for the presumed endocrine function of the salivary gland. Daily injections of 3 mg/rat of parotin or the subunit allow normal epiphyseal endochondral osteogenesis in salivary gland-deprived rats. The active agent appears to be secreted by the salivary acinar cells and resorbed through the striated ducts. Pancreatic islets and striated ducts of salivary glands share immunohistochemical activities for insulin, glucagon, and the subunit of parotin. Hyperglycemia and hypocholesterolemia occur in intact rats given 5 mg/day of parotin for 30 days. Together these data suggest endocrine functions of the salivary gland and possible interactions between the pancreatic islet and salivary gland.

Specific phosphorylation of a protein in calcium accumulating endoplasmic reticulum from rat parotid glands following stimulation by agonists involving cAMP as second messenger

Stimulation of secretion in exocrine cells by agonists involving cAMP as second messenger is associated with the phosphorylation of a specific membrane-associated 22.4-kDa protein (protein III) (Jahn et al.). Here it is shown by subcellular fractionation of rat parotid gland lobules that protein III is associated with the endoplasmic reticulum. The submicrosomal fractions containing protein III, also contain the ATP-dependent microsomal calcium pump activity. Protein III in microsomal subfractions can be phosphorylated in vitro with catalytic subunit from cAMP-dependent protein kinase. Phosphorylated protein III contains exclusively P-serine. Protein III can be removed from ER-membranes with acid chloroform-methanol or Triton X-114, but not by high salt wash indicating that it is tightly associated with the membranes. Protein III is smaller than phospholamban and, in contrast to phospholamban, resistant to heating in SDS. A relationship between phosphorylation of protein III and microsomal calcium sequestration is discussed.

[Quantitative functional scintigraphy of the salivary glands. I. Determination of global and regional gland function]

A method for quantifying the function of the salivary glands using the dynamic scintigraphy with 99mTc is presented. After a special back-ground subtraction, the net-time-activity curves of the glands are characterized by 4 quantitative parameters, describing the ability of the glands to accumulate and to excrete the tracer. As a basis for clinical application, normal values are determined and their reproducibility is discussed. To demonstrate also regional functional differences within a single gland, phase-and gradient images are suggested.

Does calmodulin mediate stimulus-secretion coupling in the parotid gland? Studies using trifluoperazine

Calmodulin present in rat parotid homogenates activated cyclic AMP phosphodiesterase activity by 8 to 10 fold. The activation was Ca2+-dependent and reversed by trifluoperazine. Half-maximal inhibition required 12 microM trifluoperazine. Incubation of parotid slices with up to 40 microM trifluoperazine had no effect on the basal rate of amylase and K+ release or on cellular ATP content. Isoproterenol stimulated glucose utilization and substance P stimulated amylase secretion were also unaffected by 40 microM trifluoperazine. 20 or 40 microM Trifluoperazine however inhibited amylase secretion induced by isoproterenol, dibutyryl cyclic AMP, carbamoylcholine or phenylephrine. The possible involvement of calmodulin in regulating enzyme secretion following stimulation of the parotid gland with the various types of agonists is discussed.

The use of lead as an ionic tracer for investigating routes of passive fluid transfer

Several inorganic ions, including lead, barium, silver, and thallium, have been tested as possible tracers for demonstrating fluid-accessible channels in functional epithelia at the ultrastructural level. The most useful of the ionic tracers examined was the lead (plumbous) ion, administered for short time intervals (less than 2 min) and "captured" with phosphate used as the buffer in the fixative. Passive fluid and ion-accessible channels of rat parotid salivary gland have been examined with this method. At short tracer infusion times (0.5-1.0 min), localization of the tracer was primarily extracellular, although intracellular deposits were observed in the following sites: smooth membrane-delimited endocytic vesicles of both epithelial and connective tissue cells, inner Golgi cisternae, and occasional cisternae of rough endoplastic reticulum. The lead tracer readily penetrated tight junctions between parotid acinar cells but rarely passed through the tight junctions between intercalated duct cells and did not penetrate junctions of striated duct cells. Fat cells observed in the stroma of this gland were the only cells that exhibited lead tracer in the cytosol, suggesting that the plasmalemma of this cell type is more permeable to exogenous ions than the plasmalemma of other cell types present in this gland.

Voltage and Ca2+-activated K+ channel in baso-lateral acinar cell membranes of mammalian salivary glands

Nervous or hormonal stimulation of many exocrine glands evokes release of cellular K+ (ref. 1), as originally demonstrated in mammalian salivary glands2,3, and is associated with a marked increase in membrane conductance1,4,5. We now demonstrate directly, by using the patch-clamp technique6, the existence of a K+ channel with a large conductance localized in the baso-lateral plasma membranes of mouse and rat salivary gland acinar cells. The K+ channel has a conductance of approximately 250 pS in the presence of high K+ solutions on both sides of the membrane. Although mammalian exocrine glands are believed not to possess voltage-activated channels1,7, the probability of opening the salivary gland K+ channel was increased by membrane depolarization. The frequency of channel opening, particularly at higher membrane potentials, was increased markedly by elevating the internal ionized Ca2+ concentration, as previously shown for high-conductance K+ channels from cells of neural origin8-10. The Ca2+ and voltage-activated K+ channel explains the marked cellular K+ release that is characteristically observed when salivary glands are stimulated to secrete.

[Differentiated effect of the qualities of sweet and sour on parotid secretion]

Taste was considered as an isolated cephalic regulatory moment in parotid salivary secretion. A different salivary response was obtained due to specific taste qualities. "Sweet" taste showed to exert a beta-adrenergic-like stimulatory effect on parotid secretion contrary to "sour" which showed a parasympathicometic effect. A correlation between the intensity of taste sensation and the parotid secretion could not be found; therefore, the taste-mediated parotid secretory response primarily seems to be of the gustatory subcortical reflex type. The central nervous mediated parotid secretory response via vagus appears to be of minor importance.

Endocytic pathways at the lateral and basal cell surfaces of exocrine acinar cells

In parotid acinar cells, horseradish peroxidase (HRP) administered via the main excretory duct is endocytosed from the apical cell surface in smooth C- or ring-shaped vesicles (Oliver, C. and A. R. Hand. 1979. J. Cell Biol. 76:207). These vesicles ultimately fuse with lysosomes adjacent to the Golgi apparatus. The present investigation extends these findings and examines the uptake and fate of intravenously injected HRP from the lateral and basal cell surfaces of resting and stimulated parotid and pancreatic acinar cells from rats and mice. Isoproterenol and pilocarpine were used to stimulate the parotid gland and the pancreas, respectively. HRP was internalized in smooth and coated vesicles primarily in areas of membrane infoldings. Both the number of coated vesicles and the amount of tracer internalized increased markedly following secretagogue administration. In both resting and stimulated cells, the HRP was rapidly sequestered in a unique system of basally located lysosomes that possess trimetaphosphatase activity, but not acid phosphatase activity. At 1-3 h after HRP administration, reaction product was also found in multivesicular bodies, vesicles, and lysosomes adjacent to the Golgi apparatus. With time, more HRP was localized in Golgi-associated lysosomes. By 6-7 h, tubules in the apical cytoplasm of stimulated cells contained HRP reaction product. When native ferritin was administered retrogradely and HRP injected intravenously, both tracers could be localized in the same lysosome after 4-5 h, indicating that material taken in from all cell surfaces mixes in Golgi-associated lysosomes. The results of this study suggest that two separate and distinct endocytic pathways exist in exocrine acinar cells: one involves membrane retrieval from the apical cell surface; and the other is a stimulation-dependent process at the lateral and basal cell surfaces.

[The relevance of the chorda tympani to parotid gland function]

In 29 patients with unilateral lesions of the chorda tympani, the parotid reflex secretions of both sides were simultaneously collected and analyzed. The median value of the flow rate (ml/15 min) of the homolateral parotid gland was reduced to nearly one-half, as compared with the unaltered contralateral side. Concentrations of amylase and protein were not significantly different. Those secretory fibres which join the facial nerve in its intratemporal course seem to reach the parotid gland mainly via the chorda tympani and, to a lesser extent, via the facial nerve directly.

Histology and histochemistry of the parotid and the principal and accessory submandibular glands of the little brown bat

The parotid and the principal and accessory submandibular glands of the little brown bat. Myotis lucifugus (Vespertilionidae), were examined using light microscopy and staining methods for mucosubstances. The parotid gland is a compound tubuloacinar seromucous gland. Parotid gland secretory cells contain both neutral and nonsulfated acidic mucosubstances. The principal and accessory submandibular glands are compound tubuloacinar mucus-secreting glands. They contain somewhat atypical mucus-secreting demilunar cells that often appear to be interspersed between mucous tubule cells. The mucous tubule cells in both the principal and accessory submandibular glands contain sulfonmucins. Demilunar cells of the principal submandibular gland contain moderate amounts of nonsulfated acidic mucosubstances, but the corresponding cells of the accessory submandibular gland contain considerable neutral mucosubstance with very little acid mucosubstance. Intercalated ducts composed of cuboidal or low columnar epithelial cells are present in all three glands. Striated ducts in all glands are composed of columnar cells whose apices bulge into the ductal lumina. Excretory ducts are composed of simple columnar epithelium, with occasional basal cells that suggest a possible pseudostratified nature. The cells of the excretory ducts also have bulging apices. All duct types contain apical cytoplasmic secretory material that is a periodic acid-Schiff positive, neutral mucosubstance. Ductal apical secretory material is more evident in intercalated and striated ducts than in excretory ducts.

Parotid acinar cells: ionic dependence of isoprenaline-evoked membrane potential changes

The effect of microionophoretic application of isoprenaline on membrane potential and resistance of mouse parotid acinar cells was investigated. For measurements of membrane resistance and the isoprenaline equilibrium potential (Eiso), two microelectrodes were inserted into neighbouring communicating cells. Passing direct current through one of these electrodes, the resting potential could be set at desired levels and Eiso was determined by plotting the relation between the size of the isoprenaline-evoked potential change and the resting potential. Simple depolarizations were found at relatively high resting potentials, while biphasic potential changes in response to isoprenaline (hyperpolarization followed by depolarization) were observed at low resting potentials. Both depolarizing and hyperpolarizing responses to isoprenaline were accompanied by a reduction of membrane resistance. The isoprenaline equilibrium potential in the initial phase of the response was about -53 mV, but had a value of about -24mV in the delayed phase. The initial isoprenaline-evoked potential change was sensitive to alterations in extracellular Na, K and Cl concentrations. The delayed depolarizing response to isoprenaline was markedly reduced by replacing extracellular Na by Tris or extracellular Cl by SO4. These results indicate that isoprenaline opens up conductance pathways permeable to Na and K.

Human parotid saliva protein composition: dependence on physiological factors

The relative concentrations of the major proteins in human parotid saliva as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis varied greatly between the six individuals included in this study but were remarkably constant for a given individual. Individual relative parotid protein concentrations differed in salivas collected under unstimulated and stimulated conditions but were at least partially independent from circadian and feeding effects. In addition, the relative concentrations of certain salivary proteins decreased with continued lemon-drop stimulation. A total of 29 different bands was composited from the six subjects. Five of the bands had mobilities corresponding with those of calibration proteins selected for their known occurrence in parotid saliva. Only those proteins comprising at least 0.75% of the total protein concentration were detected. Relative protein concentrations of parotid saliva samples collected 12 mo apart from given individuals were identical.

Amylase released from the parotid gland by pilocarpine elevates the enzyme activity in the submandibular and sublingual glands of rats

Stimulation by pilocarpine led to a marked increase in amylase activity in the submandibular and sublingual glands and serum, and resulted in a considerable depletion of the enzyme in the parotid gland and pancreas of rats. Parotidectomy reduced these pilocarpine effects. It is concluded that amylase released by pilocarpine from the parotid gland but not from the pancreas elevated the enzyme activity in the submandibular and sublingual glands.

Mechanisms of increase in amylase activity in rat submandibular and sublingual glands after administration of pilocarpine

The increase in parotid rather than pancreatic-type amylase activity in the submandibular and sublingual glands of rats caused by administration of pilocarpine was abolished or diminished when pilocarpine was injected into rats which had been parotidectomized, sympathectomized by superior cervical ganglionectomy or pretreated with reserpine. These results suggest that the increases in amylase activity in the submandibular and sublingual glands by pilocarpine are not due to increase in enzyme synthesis, but to uptake of enzyme released into the blood in large quantities from the parotid gland and that the release from the parotid gland by pilocarpine is primarily mediated by sympathetic nerves.

Receptor regulation of calcium release and calcium permeability in parotid gland cells

The mechanism by which hormones and neurotransmitters regulate fluid secretion in exocrine glands apparently involves the regulation of transmembrane movements of electrolytes, a process for which Ca serves as a second messenger. Analysis of the kinetics of efflux of 86Rb+ (a marker for K+) indicates that the initial phase of the response to secretagogues is mediated through the release of Ca from a cellular pool inaccessible to chelating agents. By investigating the movements of 45Ca under nearly steady-state conditions, we find that this cellular pool can be filled from the extracellular space without a concomitant elevation in ionized intracellular Ca2+. This suggests that the cellular pool is probably associated with the plasma membrane. We have also investigated the possible role of phosphatidic acid in the mechanism by which receptors mobilize Ca2+. Our results suggest that phosphatidic acid, formed on receptor activation, may directly mediate Ca influx into the acinar cell.

Topology of morphologically detectable protein and cholesterol in membranes of polypeptide-secreting cells

The freeze-fracture morphology of intracellular and plasma membranes in endocrine and exocrine polypeptide-secreting cells has been studied to detect changes while these membranes interact during secretion. A qualitative and quantitative evaluation of intramembrane particles and filipin binding as indicators of protein and cholesterol content of the membranes, respectively, reveals the following changes. From the forming of the maturing pole of the Golgi complex, membranes lose morphologically detectable protein and gain morphologically detectable cholesterol. The protein-poor, cholesterol-rich secretory granule membrane then interacts with a richly particulate plasma membrane in endocrine cells and with a moderately particulate luminal membrane in exocrine cells. The site of interaction between secretory granule and plasma membrane is characterized by a local clearing of intramembrane particles; by contrast, filipin-binding sites revealing cholesterol are present in this area. In exocrine cells, the fused secretory granule, which is initially rich in filipin-cholesterol complexes and poor in particles, appears to lose progressively its filipin labelling to resemble the poorly labelled luminal membrane. These findings, although they cannot be interpreted definitely at present, clearly show impressive changes of membrane structure along the secretory pathway and suggest that a corresponding degree of functional specialization is needed for proper interaction to occur.

[Interstitial gel hydration and its effect on the terminal portions and periacinar blood capillaries of the parotid salivary gland]

Swelling of the interstitial gel of the parotid salivary gland is modelled by means of perfusing its ducts under various hydrostatic pressure. Connection of this swelling with the size of the terminal secretory portions of the parotid salivary gland and with the size of the lumen in the periacinar blood capillaries is investigated by means of regression equations of the second degree. The size of the terminal portions decreases linearly, while the caliber of the blood capillaries demonstrates a parabolic dependence from the gel volume, when the interstitial gel is swelled. A conclusion is made that the swelled interstitial gel affects the terminal secretory portions of the gland by means of their simple mechanical compression, while the interconnection between the interstitial gel and the periacinar blood capillaries is of a more complicated character and cannot be understand without taking into account certain physico-chemical properties of the interstitial space and changes in intracapillary pressure.