Dispersed bovine parathyroid cells

D-l Dopamine Receptor-Mediated Activation oi Adenylate Cyclase, cAMP Accumulation, and PTH Release in Dispersed Bovine Parathyroid Cells... 

Dopamine Enhances PTH Secretion in Dispersed Bovine Parathyroid Cells... 

Dopamine causes a 20 to 30-fold increase in the content of cAMP in dispersed bovine parathyroid cells (Figure 4) (ft). 

Figure 1. Stimulation of PTH release from dispersed bovine parathyroid cells by dopamine. Cells were incubated with (M) or without ( j 1 /tM dopamine, and PTH release was determined by radioimmunoassay.

Figure 4. Stimulation of cAMP accumulation in dispersed bovine parathyroid cells by varying concentrations of dopamine (O), 6,7-ADTN (Cl), SKF 38393 (A), or apomorphine (9). (Reproduced with permission from Ref. 10. Copyright 1980, American Society for Pharmacology and Experimental Therapeutics.)...

Figure 5. Stimulation of intracellular (0) and extracellular (O) cAMP by 10 /tM dopamine in dispersed bovine parathyroid cells. cAMP was determined by radioimmunoassay.

Both calmodulin and a calcium- and calmodulin-dependent phosphodiesterase activity occur in dispersed bovine parathyroid cells (20.). Some of the phenothiazines blocking the dopamine receptor in this tissue inhibit the interaction between calmodulin and the calmodulin-dependent phosphodiesterase. A series of experiments have tested the possibility that calmodulin might play a role in the effects of these agents on the parathyroid gland. The dopamine antagonists examined were weak inhibitors of calmodulin-stimulated phosphodiesterase activity (Table II). 

In 1977, Brown et al. (15) reported that dopamine (10-8 M) stimulates by 2-4 fold the secretion of parathormone from dispersed bovine parathyroid cells. 

ADTN and other dopamine agonists mimicked this effect which was antagonized by a- and B-flupenthixol, the a-isomer being 100 times more potent. In a similar way, dopamine caused a rapid 20-30-fold increase in cellular cAMP in dispersed bovine parathyroid cells. The potency of a series of dopaminergic agonists and antagonists on adenylate cyclase activity paralleled the effects of these ligands on CAMP accumulation and parathormone secretion (16). It was concluded that bovine parathyroid cells possess dopamine sites which are involved in the control of parathormone secretion. 

Brown, E. M., Hurwitz, S., and Aurbach, G. D., 1978, a-Adrenergic inhibition of cAMP accumulation and PTH release from dispersed bovine parathyroid cells. Endocrinology 103 893... 

The cellular and molecular events involved in the dopamine-stimulated release of PTH can be clarified in experiments utilizing bovine parathyroid cells dispersed with collagenase and DNase (ft). This dispersion procedure yields parenchymal cells with only a slight contamination by red blood cells. The parenchymal cells exclude trypan blue and appear normal by light and electron microscopy (ft). These cells release PTH in a linear fashion for several hours the release is inhibited by calcium and stimulated by dopamine and beta-adrenergic agonists at concentrations comparable to those used to elicit physiological responses in vivo (ft,ft). 

In other cell types, guanine nucleotides interact with a guanine nucleotide subunit (G- or Ng-subunit) to translate receptor stimulation into increased adenylate cyclase activity (12.) Cholera toxin inhibits a specific GTPase on this guanine nucleotide subunit and thereby increases adenylate cyclase activity (13.). In dispersed cells from the bovine parathyroid gland, cholera toxin markedly increases cAMP formation and causes a 3 to 10-fold increase in the apparent affinity cf dopamine for its receptor (as determined by cAMP accumulation or IR-PTH secretion (J y.). The effects of guanine nucleotides and cholera toxin on cAMP accumulation in parathyroid cells result from interactions with the guanine nucleotide subunit in this cell. 

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