Dispersed Parotid Acinar Cells Research Articles

Potentiation by isoproterenol on carbachol-induced K+ and Cl- currents and fluid secretion in rat parotid.

Isoproterenol (IPR) and 8-(4-chlorophenylthio)-cyclic AMP (cpt-cAMP) enhanced carbachol (CCh)-induced fluid secretion from rat parotid glands, but had no effect by themselves. The enhancement by IPR was blocked by propranolol. In dispersed parotid acinar cells, IPR and cpt-cAMP potentiated CCh-induced K+ and Cl- currents (IK and ICl). IPR at the concentration of 0.1 microM significantly potentiated the CCh-induced increase in intracellular Ca2+ concentration ([Ca2+]i), but 1 mm cpt-cAMP did not. The incidence of the potentiation by IPR in CCh-induced Mn2+ entry was 31% and that by cpt-cAMP was 21%. The potentiation by IPR in the ionic currents and the [Ca2+]i was suppressed by propranolol. These results suggest that the CCh-induced fluid secretion from rat parotid glands is enhanced by IPR through the potentiation of IK and ICl mainly by the increased cyclic AMP level and partially by the potentiated Ca2+ influx and [Ca2+]i increase, and that IPR is more effective than cpt-cAMP in the enhancement of the CCh-induced [Ca2+]i increase.

The effects of substance P and carbachol on inositol tris- and tetrakisphosphate formation and cytosolic free calcium in rat parotid acinar cells. A correlation between inositol phosphate levels and calcium entry.

Both substance P and carbachol produced increases in inositol tris- and tetrakisphosphate and increased cytosolic free [Ca2+] in dispersed parotid acinar cells loaded with fura-2. The increase in [Ca2+]i in response to each agonist was due to a combination of mobilization of internal Ca2+ and entry of extracellular Ca2+. Kinetic studies of the initial response to substance P, and measurement of peak [Ca2+]i, demonstrated that the initial rapid rise in [Ca2+]i was due to both internal release and entry of Ca2+. Substance P could evoke a greater initial increase in [Ca2+]i and inositol trisphosphate than could carbachol. However, after 1 min in the presence of external Ca2+, the maintained [Ca2+]i level in response to substance P was considerably smaller than that seen with carbachol, an effect apparently due to homologous desensitization of the substance P receptor. The two agonists each produced a similar 4-5-fold increase in inositol tetrakisphosphate levels within 30 s; this level was maintained in the presence of carbachol, but decreased with substance P. Similarly, the level of inositol (1,4,5)-trisphosphate decreased after prolonged incubation with substance P. Thus, the maintained level of [Ca2+]i, and by deduction Ca2+ entry, correlated with the levels of inositol (1,4,5)-trisphosphate and inositol tetrakisphosphate; a result consistent with a possible role for these inositol phosphates in the control of receptor-mediated Ca2+ channels.

Uptake and secretion of technetium pertechnetate by the rat parotid gland

1. 1. The ability of acinar cells of the rat parotid gland to transport technetium pertechnetate ( 99mTcO − 4) was examined. 2. 2. After intravenous injection, 99mTcO − 4 was rapidly detected in parotid saliva. 3. 3. There was an excellent correlation between saliva and plasma 99mTcO − 4 levels. The saliva to plasma ratio was always < 1, consistent with the inability of rat parotid gland duct cells to concentrate the anion. 4. 4. Output of 99mTcO − 4 by the parotid gland closely mimicked fluctuations in parotid saliva flow rate. 5. 5. In vitro, enzymatically dispersed parotid acinar cells accumulated 99mTcO − 4 from the incubation medium in a biphasic manner. This uptake was partially blocked by 10 −4 M NaI. 6. 6. Cells which had accumulated 99mTcO − 4showed increased radionuclide efflux after exposure to 10 −5 M carbachol.

Potassium release by α2-adrenergic receptor stimulation of rat parotid acinar cells

alpha-Adrenergic stimulation elicited a rapid release of K+ from dispersed parotid acinar cells in the presence of external Ca2+. A recent classification of alpha-adrenergic receptors proposed that alpha 1 receptors facilitate Ca2+ entry while alpha 2 receptors interact with adenylate cyclase. We tested this proposal by studying the ability of selective alpha-adrenergic antagonists to prevent epinephrine-induced release of K+ from parotid cells. The alpha 1 agents, WB 4101 and prazosin, were less potent than the alpha 2 antagonist yohimbine. These data suggest that alpha 2-adrenergic receptors in the parotid might facilitate the entry of Ca2+.

Adrenergic and cholinergic mediated glucose oxidation by rat parotid gland acinar cells during aging

Adrenergic (both α and β) and cholinergic agonists stimulated glucose oxidation in dispersed parotid acinar cells obtained from various aged rats. Basal levels of glucose oxidation were constant over the adult rat life span. Epinephrine and norepinephrine effects on parotid cell glucose oxidation were reduced about 50% in cells from 24 mo rats compared to results with 3 and 12 mo rats. The epinephrine effect was mediated primarily via the α-adrenergic system. In addition, an α-adrenergic agonist (phenylephrine) stimulated glucose oxidation significantly less in parotid cells from 24 mo rats than in those from younger rats. β-Adrenergic (isoproterenol) and cholinergic (carbachol) stimulation did not change with age. These results suggest that an age-related impairment occurs specifically in the α-adrenergic system of rat parotid acinar cells.

The relationship between muscarinic receptor binding and ion movements in rat parotid cells.

1. The relationship of muscarinic receptor binding to ion fluxes induced by muscarinic agonists was investigated in rat parotid cells. 2. Receptor binding was measured with [3H]quinuclidinyl benzilate in living, dispersed parotid acinar cells. These same cells were used to determine concentration-effect relationships (ion fluxes) for agonists. 3. Receptor binding of antagonists accurately reflected the pharmacologically determined affinities. In the case of agonists, apparent pharmacological affinities were greater than binding affinities by a factor of 12.5 for methacholine and 18.7 for carbachol. 4. The reason for the discrepancy between agonist binding and effect is not known with certainty, but the existence of "spare" receptors is considered a possibility. 5. The total number of muscarinic receptors is estimated to be 23,000/cell. If some are spare, as few as 1800/cell may suffice to fully activate the available Ca channels.

Retention of nerve terminals in dispersed parotid acinar cells

The effects of veratridine, an agent known to increase Na permeability in excitable tissues, were determined on a dispersed cell preparation from the rat parotid gland. The uptake of 22Na by these parotid cells was increased in the presence of veratridine but not to as great an extent as with carbachol. The veratridine effect was blocked by both tetrodotoxin (TTX) and a combination of receptor blockers, atropine and phentolamine. TTX had no effect on the increase in 22Na uptake due to carbachol. Electron microscopic examination revealed the presence of nerve terminals in the dispersed cell preparation, often in very close apposition to individual cells. It is likely that these nerve terminals are the primary sites of actions of veratridine and TTX and not the parotid acinar cells. The possibility of the presence of unmyelinated nerve fibers should be taken into account in the analyses of experimental data obtained with dispersed cell preparations.