Beta-adrenergic receptor mechanisms in rat parotid glands: activation by nerve stimulation and 3-isobutyl-1-methylxanthine.

The possibility that old and new secretory granules do not mix and that older exportable protein can be secreted preferentially was tested on parotid gland in vitro. Slices from fasted animals were pulse labeled for 3 min with L-[3H]leucine. Subcellular fractionstion showed that after 1 90-min chase period, the formation of new labeled secretory granules was mostly completed. The ratio of label in secretory granules to label in microsomes increased 250-fold during the period 5--90 min postpulse. After the 90-min chase, a submaximal rate of secretion was initiated by adding a low concentration of isoproterenol to the slices. Preferential secretion of old unlabeled exportable protein was evident from the finding that the percent of total amylase secreted was 3.5-fold greater than the percent of labeled protein secreted. Preferential secretion of old unlabeled exportable amylase was undiminished even when the chase period before addition of isoproterenol was extended to 240 min. Such long chase incubations were still meaningful due to the fact that the spontaneous rat of amylase release and radioactive protein release from the slices was negligibly low. A high isoproterenol concentration added to the slices after a 90-min chase produced the following results. An initial phase of preferential secretion of old unlabeled protein was soon replaced by secretion of a random mixture of new and old exportable protein. Electron micrographs indicated that high rates of secretion involved sequential fusion of secretory granules so that the lumen extended deep into the cell where the new labeled granules were presumably located. At low rates of secretion, the lumen showed no such deep extensions. Experiments were also conducted on slices from glands which had been largely depleted of old granules by prior injection of isoproterenol into the animals. Secretion of labeled protein from such slices stopped with the export of 80% of the labeled protein. This finding indicates that about 20% of the radioactive protein is cellular nonexportable protein and that the slices are capable of exporting the entire amount of secretory protein which was symthesized in vitrol. In addition to the beta-adrenergic receptor which mediates protein secretion, the parotid acinar cell also possesses an alpha-adrenergic and a cholinergic receptor both of which cause K+ release, vacuole formation, and water secretion. Activation of either of the latter two receptors in conjunction with the beta-adrenergic receptor increased randomization of the protein secreted. It is concluded that in the rat parotid acinar cell there is little spontaneous mixing between old granules near the luminal cell membrane and new granules coming up behind from the Golgi complex. The neurotransmitters which induce secretion produce the observed randomization.

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Failure of Beta-Adrenergic Receptor Blockade to Prevent Arrhythmias Induced by Sympathetic Nerve Stimulation

Science ◽

10.1126/science.185.4145.70 ◽

1974 ◽

Vol 185 (4145) ◽

pp. 70-72 ◽

Cited By ~ 15

Author(s):

R. A. Gillis ◽

D. L. Pearle ◽

T. Hoekman

Keyword(s):

Nerve Stimulation ◽

Sympathetic Nerve ◽

Adrenergic Receptor ◽

Receptor Blockade ◽

Beta Adrenergic Receptor ◽

Sympathetic Nerve Stimulation ◽

Beta Adrenergic ◽

Adrenergic Receptor Blockade

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Forskolin, a tool for rat parotid secretion studies: 45Ca efflux is not related to cAMP

AJP Cell Physiology ◽

10.1152/ajpcell.1986.251.5.c754 ◽

1986 ◽

Vol 251 (5) ◽

pp. C754-C762 ◽

Cited By ~ 12

Author(s):

C. Dreux ◽

V. Imhoff ◽

C. Huleux ◽

S. Busson ◽

B. Rossignol

Keyword(s):

Adrenergic Receptor ◽

Receptor Activation ◽

Camp Level ◽

Induced Response ◽

Beta Adrenergic Receptor ◽

Beta Adrenergic ◽

Level Increase ◽

Rat Parotid Gland ◽

Rat Parotid ◽

45Ca Efflux

In the present work, we investigated, by use of forskolin, whether adenosine 3',5'-cyclic monophosphate (cAMP) level and Ca movements were modulated sequentially or in parallel by the activation of the beta-adrenergic receptor in the rat parotid gland. Forskolin-induced [3H]protein secretion was dependent on external Ca, whereas isoproterenol-induced secretion was not. This effect was not due to a requirement of adenylate cyclase for Ca, since the cAMP level increase induced by forskolin was not Ca dependent. Furthermore isoproterenol induced 45Ca efflux, whereas forskolin did not. 45Ca efflux was correlated neither to cAMP nor to secretion, since when there was a massive augmentation of cAMP there was no change in 45Ca efflux, and forskolin, which induced much secretion, was unable to induce Ca efflux. Carbachol potentiated the secretion induced by forskolin in the absence of Ca, whereas it did not potentiate the isoproterenol-induced response. From these results we suggest that beta-adrenergic receptor activation would lead to two parallel events, cAMP accumulation and Ca movements, which together would lead to maximal secretion.

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