Calcium entry in rat parotid acinar cells.
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Animals↗
Biomedical subjects
B J Baum
Publications and source records attributed to B J Baum.
Membrane potential modulates divalent cation entry in rat parotid acini.
This study examines the effect of membrane potential on divalent cation entry in dispersed parotid acini following stimulation by the muscarinic agonist, carbachol, and during refill of the agonist-sensitive internal Ca2+ pool. Depolarizing conditions (addition of gramicidin to cells in Na(+)-containing medium or incubation of cells in medium with elevated [K+]) prevent carbachol-stimulated hyperpolarization of acini and also inhibit carbachol activation of Ca2+ and Mn2+ entry into these cells. Conditions promoting hyperpolarization (cells in medium with Na+ or with N-methyl-D-glucamine instead of Na+) enhance carbachol stimulation of divalent cation entry. Intracellular Ca2+ release (initial increase in [Ca2+]i) does not appear to be affected by these manipulations. Mn2+ entry into resting and internal Ca2+ pool-depleted cells (10-min carbachol stimulation in a Ca(2+)-free medium) is similarly affected by membrane potential modulations, and refill of the internal pool by Ca2+ is inhibited by depolarization. The inhibitory effects of depolarization on divalent cation entry can be overcome by increasing extracellular [Ca2+] or [Mn2+]. These data demonstrate that the modulation of Ca2+ entry into parotid acini by membrane potential is most likely due to effects on the electrochemical gradient (Em-ECa) for Ca2+ entry.
Animals↗
Elevation of cytosolic [Ca2+] due to intracellular Ca2+ release retards carbachol stimulation of divalent cation entry in rat parotid gland acinar cells.
This study examines the activation of divalent cation entry into rat parotid gland acinar cells by using Mn2+ as a Ca2+ surrogate cation. Following muscarinic-cholinergic stimulation of dispersed parotid acini with carbachol (10 microM), the onset of internal Ca2+ release (cytosolic [Ca2+], [Ca2+]i, increase) and the stimulation of Mn2+ entry (increase in fura2 quenching) are not simultaneously detected. [Ca2+]i elevation, due to intracellular release, is detected almost immediately following carbachol addition and peak [Ca2+]i increase occurs at 6.0 +/- 0.8 sec. However, there is an interval (apparent lag) between carbachol addition and the detection of stimulated Mn2+ entry. This apparent lag is decreased from 26 +/- 3.1 sec to 9.2 +/- 1.5 sec when external Mn2+ ([Mn2+]0) is increased from 12.5 to 500 microM. It is not decreased further with increase in [Mn2+]0 from 500 microM to 1 mM (9.8 +/- 2.1 sec), although both intracellular free Mn2+ and [Mn2+-fura2]/[fura2] increase. Thus, at [Mn2+]0 < 500 microM, the observed lag time is partially due to a limitation in the magnitude of Mn2+ entry. Furthermore, neither peak [Ca2+]i nor the time required to reach peak [Ca2+]i is significantly altered by [Mn2+]0 (12.5 microM to 1 mM). At every [Mn2+]0 tested (i.e., 12.5 microM-1 mM), the apparent lag is significantly greater than the time required to reach peak [Ca2+]i. However, when carbachol stimulation of the [Ca2+]i increase is attenuated by loading the acini with the Ca2+ chelator, 2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA), there is no detectable lag in carbachol stimulation of Mn2+ entry (with 1 mM [Mn2+]0). Importantly, in BAPTA-loaded acini, carbachol stimulates Mn2+ entry via depletion of the internal Ca2+ pool and not via direct activation of other divalent cation entry mechanisms. Based on these results, we suggest that the apparent lag in the detection of carbachol stimulation of Mn2+ entry into parotid acinar cells is due to a retardation of Mn2+ entry by the initial increase in [Ca2+]i, due to internal release, which most likely occurs proximate to the site of divalent cation entry.
Androstenedione↗
Characterization of polyphosphoinositide-specific phospholipase C in rat parotid gland membranes.
Hydrolysis of exogenously added, [3H]inositol-labeled, phosphatidylinositol 4,5-bisphosphate (PIP2) by rat parotid membranes was increased, dose-dependently, by the muscarinic cholinergic agonist carbamylcholine (carbachol) in the presence of guanosine 5'-O-thiotriphosphate (GTP gamma S). The stimulation was inhibited by atropine and guanosine 5'-O-thiodiphosphate (GDP beta S). GTP gamma S alone stimulated PIP2 hydrolysis, with half-maximal activation at 0.1 microM. This was inhibited by GDP beta S but not by atropine. Agonist stimulation of PIP2 hydrolysis was dependent on the presence of lipids (phosphatidylserine:phosphatidylethanolamine:PIP2 = 1:1:1). When PIP2 was added as micelles with detergent (sodium deoxycholate) only, basal hydrolysis was elevated, thus decreasing the relative stimulation by GTP gamma S and carbachol. The water-soluble hydrolysis products formed under either condition were 1,4,5-inositol trisphosphate, 1,4-inositol bisphosphate, and cyclic inositol trisphosphate. Hydrolysis of exogenous phosphatidylinositol (PI) was also stimulated by carbachol in the presence of GTP gamma S but the extent of PI hydrolysis was 44-fold lower than PIP2 hydrolysis. When [Ca2+] in the medium was increased from 100 nM to 1 microM, basal hydrolysis of both PI and PIP2 increased (9.3- and 19.2-fold, respectively). However, levels of basal and stimulated PIP2 hydrolysis were higher (37.9- and 29.6-fold, respectively) than those of PI hydrolysis. Antibodies (both polyclonal and monoclonal) raised against phospholipase C (PLC beta 1) from bovine brain did not react with any component in either rat parotid membranes or cytosol, although a reactivity was detected in rat brain membranes. A monoclonal antibody against bovine brain PLC gamma 1 detected a approximately 150-kDa protein only in the parotid cytosol, while antisera against bovine brain PLC delta 1 enzyme showed no reactivity with parotid membranes or cytosol. Together, these observations suggest that while there appears to be a protein similar to bovine brain PLC gamma 1 in parotid gland cytosol, the PLC which mediates PIP2 hydrolysis in rat parotid membranes and can be regulated by the muscarinic receptor via a G-protein is distinct from the well-characterized PLC enzymes gamma 1, delta 1, and beta 1.
Animals↗
Glandular-like morphogenesis of the human submandibular tumor cell line A253 on basement membrane components.
We have studied the interaction of a human tumor cell line, A253, derived from a submandibular gland carcinoma with a differentiation promoting reconstituted basement membrane extract, Matrigel. When cultured on plastic, these cells maintain a flat, cobblestone, epithelial morphology. On Matrigel, A253 cells initially form a honeycomb network of cords of cells which subsequently thickens. With time, these cords of cells become discontinuous and blunted, whereupon multilobular clusters of cells develop. These clusters possess a lumen with polarized, PAS(+) cells containing numerous desmosomes and an abundance of glycogen. Culture of the cells on laminin, the most abundant protein found in Matrigel, also induces this morphologic differentiation. Using synthetic laminin-derived peptides, the biologically active IKVAV-containing site of laminin was most active in attachment assays, as well as in inhibiting glandular-like morphogenesis when added to the media of cells cultured on Matrigel. Antibodies to the cell surface 67- and 32-kDa laminin binding proteins partially inhibited the glandular-like morphogenesis, suggesting that multiple interactions with laminin are likely required for the differentiation process. Our data demonstrate that A253 cells can undergo glandular-like morphogenesis on basement membrane and that laminin appears to be the major initiating factor.
Blotting, Western↗
Salivary gland function and glucose metabolic status.
To study the relationship between glucose metabolic status and salivary gland function in different-aged persons, subjects with diabetes mellitus (DM = 11), impaired glucose tolerance (IGT = 26), and controls (n = 26), aged 24 to 93, were examined in the oral physiology component of the Baltimore Longitudinal Study of Aging. All were generally healthy (except DM) and nonmedicated. The controls and subjects with IGT were classified using World Health Organization criteria, and diabetic status was assessed using Hb1Ac levels. Unstimulated and 2% citrate-stimulated parotid and submandibular salivary flow rates were collected, and subjective responses to questions about salivary hypofunction were evaluated. No statistically significant differences were observed between the three groups, nor between young and old subjects with altered glucose metabolism. These findings suggest that among well-controlled individuals with altered glucose metabolism, salivary gland function is not significantly impaired.
Adult↗
Effect of ionizing radiation on sympathetic nerve function in rat parotid glands.
Ionizing radiation (IR) irreversibly damages salivary glands. The pathologic mechanism is unknown. Previously we reported that parotid serous acinar cells may not be the primary site of damage by IR. The purpose of this study was to determine if IR alters sympathetic nerve function in rat parotid glands. Male adult rats received a single dose of radiation (20 Gy) to the head and neck. Three days after IR, parotid saliva secretion induced by norepinephrine (NE) was completely blocked. Catecholamine uptake and metabolism were studied by injecting [3H] dopamine ([3H]DA) into irradiated rats, as a bolus. After 60 min, animals were sacrificed and the parotid gland, submandibular gland, and left ventricle removed. Tissue contents of [3H]DA and [3H]NE, identified by HPLC, were unaffected by IR. The results indicate that IR abolishes acinar responsiveness to NE without affecting parotid sympathetic nerve function.
Animals↗
Age-related vulnerability.
This presentation considers the vulnerability of the upper alimentary and respiratory tracts to environmental insults during aging. A specific example, salivary gland secretion, is discussed. Available data suggest that while aging per se does not affect salivary performance adversely, it does appear to compromise the glands in such a way that older persons are more vulnerable to exogenous factors that can reduce secretory capacity and, consequently, diminish oropharyngeal health.
Aged↗
Salivary gland function and aging: a model for studying the interaction of aging and systemic disease.
This review describes an approach to examining the interaction of aging and systemic disease on a key aspect of oral physiology, salivation. The approach requires several steps: defining general health, and a specific physiological function, at different ages; defining a disease of interest and the influence of the disease on the specific physiological function; and determining if the disease can affect performance of the physiological function with increased age.
Aging↗
Further studies of salivary inhibition of HIV-1 infectivity.
An HIV-1/ATH8-cell cytopathic system was used to characterize the previously reported anti-HIV-1 activity of human saliva. Inhibitory activity was demonstrated by monitoring viable cell counts, HIV-1 p24 core antigen, and reverse transcriptase levels. Nonfiltered whole saliva, sterilized by irradiation, protected the ATH8 cells from HIV-1 infection. When HIV-1/saliva mixtures were filtered following incubation, the quantity of virus was significantly less (approximately 50%) than in HIV-1/media-filtered controls, suggesting that salivary aggregation and/or agglutination may be involved in the inhibitory activity. However, a sufficient number of apparently morphologically intact viral particles were still present in the HIV-1/saliva filtrates to lead to infection. When saliva was filtered prior to incubation with HIV-1, these filtrates showed substantial inhibitory activity, although reduced compared with that of non-prefiltered saliva. We conclude that saliva likely has several means by which to inhibit HIV-1 infectivity.
Adult↗
Effects of ionizing radiation and beta-adrenergic stimulation on the expression of early response genes in rat parotid glands.
There is little known about the regulation of gene expression in rat parotid glands after exposure to ionizing radiation. The present studies investigate the effects of in vivo ionizing radiation, with subsequent stimulation of beta-adrenergic receptors by isoproterenol, on parotid gland function and on the expression of the early response genes, c-fos, c-jun, and jun B. Ionizing radiation diminished parotid gland weight and saliva output. Treatment of irradiated rats with isoproterenol increased the gland weight to levels similar to those in nonirradiated rats. However, such treatment had no effect on saliva output as indicated by measurements of parotid salivary flow rate. Irradiation alone increased the expression of c-fos, c-jun, and jun B. The combination of irradiation and isoproterenol had an additional effect on the levels of c-fos and jun B mRNAs and proteins particularly at earlier experimental times (1 to 8 h). Isoproterenol alone induced high levels of c-fos and jun B mRNA but not of c-jun mRNA. However, c-jun mRNA was induced markedly by radiation and 8 h of isoproterenol treatment, indicating a combined effect on c-jun gene expression. These observations suggest that the expression of the proto-oncogenes c-fos, c-jun, and jun B is probably regulated through differential signal transduction pathways which may be activated by these external stimuli and may be associated with functional changes induced in the rat parotid gland by ionizing radiation and by ionizing radiation and isoproterenol.
Animals↗
Commentary on "Education for dental practice in the year 2005: a beginning dialogue".
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Biological Science Disciplines↗
Muscarinic receptor antagonist effects in parotid acini and M1-CHO cells: evidence of G protein involvement.
We have examined the effects of the muscarinic antagonist atropine, on non-receptor-mediated activation of intracellular calcium (Ca2+i) mobilization events. In dispersed rat parotid acini, atropine significantly lowered basal inositol trisphosphate levels and delayed AlF4(-)-stimulated Ca2+i elevation in a dose-dependent manner. In a cell line transfected with the m1 muscarinic receptor (M1-CHO), atropine significantly lowered (approximately 60%) AlF4- stimulated Ca2+i elevation. These aggregate findings suggest that atropine, acting via the muscarinic receptor, decreases the efficacy of G protein-mediated activation of phospholipase C.
Animals↗
Characterization of high affinity GTPase activity correlated to beta-adrenergic receptor stimulation of adenylyl cyclase in rat parotid membranes.
beta-Adrenergic receptor stimulation of adenylyl cyclase involves the activation of a GTP-binding regulatory protein (G-protein, termed here Gs). Inactivation of this G-protein is associated with the hydrolysis of bound GTP by an intrinsic high affinity GTPase activity. In the present study, we have characterized the GTPase activity in a Gs-enriched rat parotid gland membrane fraction. Two GTPase activities were resolved; a high affinity GTPase activity displaying Michaelis-Menten kinetics with increasing concentrations of GTP, and a low affinity GTPase activity which increased linearly with GTP concentrations up to 10 mM. The beta-adrenergic agonist isoproterenol (10 microM) increased the Vmax of the high affinity GTPase component approx. 50% from 90 to 140 pmol/mg protein per min, but did not change its Km value (approximately 450 nM). Isoproterenol also stimulated adenylyl cyclase activity in parotid membranes both in the absence or presence of GTP. In the presence of a non-hydrolyzable GTP analogue, guanosine 5'-(3-O-thio)triphosphate (GTP gamma S), isoproterenol increased cAMP formation to the same extent as that observed with AlF-4. Cholera toxin treatment of parotid membranes led to the ADP-ribosylation of two proteins (approximately 45 and 51 kDa). Cholera toxin also specifically decreased the high affinity GTPase activity in membranes and increased cAMP formation induced by GTP in the absence or the presence of isoproterenol. These data demonstrate that the high affinity GTPase characterized here is the 'turn-off' step for the adenylyl cyclase activation seen following beta-adrenergic stimulation of rat parotid glands.
Adenylyl Cyclases↗
Physiologic levels of salivary epidermal growth factor stimulate migration of an oral epithelial cell line.
An established line of human oral epithelial cells exhibits chemotaxis to epidermal growth factor (EGF). The directed migration of these cells is time dependent with an approximate 10-fold increase in the number of cells responding to the chemoattractant by 6 h. Cell migration occurs in a concentration dependent manner with maximal response at approximately 1 ng/ml. This maximal chemotactic response occurs within the physiologic concentration range for EGF found in human saliva. These data suggest that EGF may be important for the maintenance of an intact oral epithelial (mucosal) barrier, and may play a vital role in oral mucosal wound healing.
Cell Movement↗
High affinity quinuclidinyl benzilate binding to rat parotid membranes requires muscarinic receptor. G protein interactions.
The binding of the non-selective muscarinic antagonist [3H]quinuclidinyl benzilate (QNB) to rat parotid membranes was characterized. Under equilibrium conditions, [3H]QNB bound to a homogenous population of muscarinic receptors (Kd, 118 +/- 19 pM; Bmax, 572 +/- 42 fmol/mg membrane protein, n = 12). The addition of G protein activators AlF4- or guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) + Mg2+ increased the Kd by 77 +/- 7% (n = 4, P less than 0.05) and 83 +/- 27% (n = 7, P less than 0.05), respectively, without a change in the Bmax or homogeneity of the binding site. GTP gamma S added without exogenous Mg2+ did not affect [3H]QNB binding. Thus, optimal QNB binding requires a muscarinic receptor/G protein interaction.
Aluminum↗
Cellular characteristics of long-term cultured rat parotid acinar cells.
We have successfully maintained and biochemically characterized differentiated rat parotid acinar cells cultured for long periods (6 mo.). The cells were cultured on a reconstituted basement membrane matrix in a medium containing a variety of agents that promote cellular proliferation and differentiation. The cultured cells retain the characteristics of the parental parotid acinar cells. They exhibit both secretory granules and abundant cellular organelles required for protein synthesis and secretion. In situ hybridization and immunocytochemistry demonstrate high levels of proline-rich protein mRNA and protein, and lower levels of amylase mRNA and protein, in their cytoplasm. These findings suggest that rat parotid acinar cells can be maintained in a differentiated state in vitro for long periods, and can serve as a useful model system for studying the regulation of exocrine secretory processes.
Amylases↗
Oral mucosal appearance is unchanged in healthy, different-aged persons.
Oral mucosal status in 182 different-aged, healthy, community-dwelling persons was evaluated. Ninety-four men and 88 women, ranging in age between 20 and 95 years, participated in this study. Oral mucosal status was assessed according to both subjective complaints and a semiquantitative clinical rating scale. No changes in either criterion were detected with increasing age. Oral mucosal status of the older subjects of this study was comparable to that found in a previous study with a randomly enrolled, noninstitutionalized older population in Iowa. The results of this study suggest that aging per se does not lead to changes in the appearance of oral mucosa.
Adult↗