Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined the rapid effects (less than 120 sec) of 1,25(OH)2D3 on membrane phospholipid hydrolysis in porcine parathyroid cells and compared these effects to those produced by extracellular Ca2+. Cells were labeled with [3H]myo-inositol or [14C]arachidonic acid for 3 h, then exposed to various 1,25(OH)2D3 concentrations in 0.5 mM Ca2+ for different time periods or to 2 mM [Ca2+]. Parathyroid cells showed a biphasic increase in diacylglycerol (DAG), monoacylglycerol (MG), phosphatidic acid (PA), and inositol trisphosphate (IP3) in response to 1,25(OH)2D3 (10(-12)-10(-8) M) or to 2 mM [Ca2+]. This effect was rapid (within 5 sec) and dose-dependent, with a maximal stimulation with 10 pM of 1,25(OH)2D3. At this concentration, the first peak of DAG, MG, and IP3 was at 5 sec and reached 176 +/- 9%, 134 +/- 4%, and 154 +/- 13%, respectively vs. basal levels. For PA, the first maximum increase was at 20 sec (130 +/- 6%). At 30 sec MG, PA, and IP3 returned to basal levels, whereas the decrease in DAG was under the basal level (-25 +/- 5%). The second peak reached a maximum at 60 sec for the four products (145 +/- 8%, 119 +/- 5%, 125 +/- 6%, and 175 +/- 20%, respectively) then decreased to basal level at 120 sec. High extracellular Ca2+ (2 mM) and fluoride (5 mM) also produced similar increase in phosphatidylinositol metabolites, except that DAG levels returned to basal level at 30 sec. In conclusion, the present data shows the existence of rapid effects of 1,25(OH)2D3 in porcine parathyroid cells. The short time sequence suggests that they are mediated by a direct interaction with the membrane, possibly through a receptor-mediated process linked to phospholipase C by a G-protein.
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PMID:Rapid effects of 1,25-dihydroxyvitamin D3 and extracellular Ca2+ on phospholipid metabolism in dispersed porcine parathyroid cells. 224 25

In parathyroid cells, high extracellular Ca2+ promotes a rapid increase in inositol trisphosphate (IP3), suggesting activation of phospholipase C. Available data, however, indicate a high Ca2+-induced decrease in sn-1,2-diacylglycerol (DG), rather than the increase expected with hydrolysis of phosphoinositides. To explore this apparent discrepancy between IP3 and DG, we used three methods to quantify DG levels in parathyroid cells in response to high Ca2+ over the time course when IP3 levels increase. A simple enzymatic method was developed for the quantitation of the mass of DG present in crude lipid extracts. The assay employed rat brain DG kinase and defined mixed micellar conditions to solubilize the DG present and allow its quantitative conversion to [32P]phosphatidic acid. [32P]Phosphatidic acid formed in the assay was directly proportional to the amount of DG added over the range of 25 pmol to 25 nmol or to the number of parathyroid cells (5 X 10(5) to 2 X 10(6) cells). Parathyroid cells were also labeled with [3H]glycerol (24 h) or [3H]arachidonic acid (2 or 18 h) and exposed to various extracellular Ca2+ concentrations for different times. The total lipids were then extracted and separated by TLC. Using each of the three methods to measure DG, parathyroid cells showed a rapid increase in DG when extracellular Ca2+ was increased from 0.5 to 2.0 or 3.0 mM. The maximal increase occurred at 5-20 s. The levels of DG at high Ca2+ then decreased to levels 20-50% higher than those at 0.5 mM Ca2+ from 60 sec to 10 min. DG levels remained higher at 2-3 mM Ca2+ than at 0.5 mM Ca2+ even at 30 min. Similar results were obtained in 10 independent experiments with the kinase method, 7 independent experiments with the [3H]glycerol method, and 12 independent experiments with the [3H]arachidonic acid method. These results show the high Ca2+ rapidly increases intracellular levels of DG as well as IP3 in bovine parathyroid cells, consistent with activation of phospholipase C. Thus, the initial rapid decrease in PTH release at high Ca2+ is not caused by a concomitant decrease in DG, but is presumably related to additional inhibitory mechanisms that override the high Ca2+-induced increases in DG and cytosolic Ca2+.
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PMID:Relationship between diacylglycerol levels and extracellular Ca2+ in dispersed bovine parathyroid cells. 284 84

Parathyroid hypertensive factor (PHF) has been purified from two sources of material: plasma of spontaneously hypertensive rats (SHRs) and culture medium from organ culture of SHR parathyroid glands. Chromatographic characteristics of PHF from these two sources are identical. Biological activity of PHF (assayed as the characteristic delayed hypertensive response in normotensive rats) is sensitive to degradation by treatment in base, and the enzymes trypsin, chymotrypsin, phospholipase C, and phospholipase D. PHF activity may also be extracted from source material with chloroform: methanol (4:1). A hypothetical structure for the active component of PHF is suggested. This is comprised of a peptide liked to a lysophospholipid.
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PMID:Purification and structural characterization of parathyroid hypertensive factor. 751 47

Parathyroid cells recognize and respond to (i.e., "sense") minute perturbations in the extracellular ionized calcium concentration (Ca2+o), but the mechanisms underlying this process have remained obscure. Recently, we employed expression cloning in Xenopus laevis oocytes to isolate a cDNA coding for a Ca2+o-sensing receptor from bovine parathyroid. Like the native receptor, the cloned Ca2+o-sensing receptor stimulates phospholipase C (PLC) in a G-protein-dependent manner with a nearly identical pharmacological profile. Its deduced amino acid sequence confirms that it is a member of the superfamily of G-protein-coupled receptors (GPR). Transcripts for the receptor are expressed in parathyroid and other tissues that sense Ca2+o (viz., kidney and thyroidal C-cells) as well as those that have no known role in extracellular Ca2+ homeostasis, such as the brain. The availability of the cDNA clone for the Ca2+o-sensing receptor made it possible to test the hypothesis that mutations in the gene encoding the human homolog of the receptor cause inherited disorders of mineral ion metabolism. Familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT) are, in fact, caused by mutations that reduce the activity of the receptor when they are present in the heterozygous and homozygous states, respectively. In contrast, we have subsequently discovered a family in which a form of autosomal dominant hypocalcemia results from an activating mutation in the receptor gene. The Ca2+-sensing receptor, therefore, permits Ca2+o to play a "hormonelike" role as an extracellular first messenger in addition to its well described role as an important intracellular second messenger.
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PMID:Cloning and functional characterization of extracellular Ca(2+)-sensing receptors from parathyroid and kidney. 857 1