251
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Manne V, Kung HF. Characterization of phosphoinositide-specific phospholipase C from human platelets. Biochem J 1987; 243:763-71. [PMID: 2821991 PMCID: PMC1147923 DOI: 10.1042/bj2430763] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Phosphoinositide-specific phospholipase C (PI-PLC) from human platelet cytosol was purified 190-fold to a specific activity of 0.68 mumol of phosphatidylinositol (PI) cleaved/min per mg of protein. It hydrolyses PI and phosphatidylinositol 4,5-bisphosphate (PIP2), but not phosphatidylcholine, phosphatidylserine or phosphatidylethanolamine. The enzyme exhibits an acid pH optimum of 5.5 and has a molecular mass of 98 kDa as determined by Sephacryl S-200 gel filtration. It required millimolar concentrations of Ca2+ for PI hydrolysis, whereas micromolar concentrations are optimal for PIP2 hydrolysis. Mg2+ could substitute for Ca2+ when PIP2, but not PI, was used as the substrate. EDTA was more effective than EGTA in inhibiting the basal PI-PLC activity towards PIP2. Sodium deoxycholate strongly inhibits the purified PI-PLC activity with either PI or PIP2 as substrate. Ras proteins, either alone or in the form of liposomes, have no effect on PI-PLC activity.
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Affiliation(s)
- V Manne
- Department of Molecular Oncology, Roche Institute of Molecular Biology, Nutley, NJ 07110
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252
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Pucell AG, Bumpus FM, Husain A. Rat ovarian angiotensin II receptors. Characterization and coupling to estrogen secretion. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)48205-1] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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253
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Renard D, Poggioli J, Berthon B, Claret M. How far does phospholipase C activity depend on the cell calcium concentration? A study in intact cells. Biochem J 1987; 243:391-8. [PMID: 2820378 PMCID: PMC1147867 DOI: 10.1042/bj2430391] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The dependence of phospholipase C activity on the cytosolic Ca2+ concentration ([Ca2+]i) was studied in intact liver cells treated with the Ca2+-mobilizing hormone vasopressin, or not so treated. Phospholipase C (PLC) activity was estimated from the formation of [3H]inositol trisphosphate (InsP3) and the degradation of [3H]phosphatidylinositol 4,5-bisphosphate (PtdInsP2). The [Ca2+]i of the cells was clamped from 29 to 1130 nM by quin2 loading. This wide concentration range was obtained by loading the hepatocytes with a high concentration of the Ca2+ indicator in low-Ca2+ medium or by using the Ca2+ ionophore ionomycin in medium containing Ca2+. In resting cells, in which [Ca2+]i was 193 nM, treatment with 0.1 microM-vasopressin which stimulates liver PLC maximally, tripled InsP3 content and raised [Ca2+]i to 2 microM within 15 s. Lowering [Ca2+]i partially decreased cell InsP3 content as well as the ability of vasopressin to stimulate InsP3 formation maximally. At 29 nM, the lowest Ca2+ concentration obtained in isolated liver cells, basal InsP3 content was 64% of that measured in control cells. Addition of vasopressin no longer affected [Ca2+]i, but significantly increased InsP3 by 200%, although less than in the controls (300%). The maintenance of the greater part of the PLC response at constant [Ca2+]i indicated that, in the liver, InsP3 formation does not result from an increase in [Ca2+]i. The effects of lowering [Ca2+]i were reversible. When low cell [Ca2+]i was restored to a normal value, resting InsP3 content and the ability of vasopressin to stimulate InsP3 formation maximally by 300% were also restored. Raising [Ca2+]i from 193 to 1130 nM had little effect on the InsP3 content or the vasopressin-mediated increase in InsP3. In agreement with the stimulation of PLC activity by vasopressin, cell [3H]PtdInsP2 and total PtdInsP2 were degraded by application of this hormone for 15 s. In contrast, when [Ca2+]i was lowered to 29 nM, basal [3H]PtdInsP2 and total PtdInsP2 were increased by about 30%, [3H]PtdInsP2 was further increased by vasopressin, but total PtdInsP2 was not changed. These results show that, in intact hepatocytes, PLC is little affected by [Ca2+]i concentrations above 193 nM, but is partially dependent on Ca2+ below that value. They suggest that, in addition to activating PLC activity, vasopressin might stimulate PtdInsP2 synthesis, presumably via phosphatidylinositol-phosphate kinase, and that this pathway might predominate in cells with low [Ca2+]i.
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254
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Guillon G, Balestre MN, Mouillac B, Berrada R, Kirk CJ. Mechanisms of phospholipase C activation: a comparison with the adenylate cyclase system. Biochimie 1987; 69:351-63. [PMID: 3115315 DOI: 10.1016/0300-9084(87)90026-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Many hormones, neurotransmitters or other signaling molecules exert their biological activities through the stimulation of a specific phospholipase C. Once activated, this enzyme hydrolyzes polyphosphoinositide into inositol trisphosphate and diacylglycerol, two products known to regulate the cytosolic calcium concentration and the activity of protein kinase C, respectively. The molecular mechanisms leading to the activation of phospholipase C after the binding of the signal molecule to its specific receptor remain unclear. Yet, recent studies demonstrated that at least three molecules were implicated: the receptor, the phospholipase C and a GTP binding protein. In this review, we have summarized the properties of such systems and, more particularly, those of the vasopressin-sensitive phospholipase C present in WRK1 cells. The existence of many functional and structural analogies for the receptors which regulate adenylate cyclase activity is discussed.
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Affiliation(s)
- G Guillon
- Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier
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255
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Murphy GJ, Hruby VJ, Trivedi D, Wakelam MJ, Houslay MD. The rapid desensitization of glucagon-stimulated adenylate cyclase is a cyclic AMP-independent process that can be mimicked by hormones which stimulate inositol phospholipid metabolism. Biochem J 1987; 243:39-46. [PMID: 3038085 PMCID: PMC1147811 DOI: 10.1042/bj2430039] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Treatment of intact hepatocytes with glucagon, TH-glucagon [( 1-N-alpha-trinitrophenylhistidine, 12-homoarginine]glucagon), angiotensin or vasopressin led to a rapid time- and dose-dependent loss of the glucagon-stimulated response of the adenylate cyclase activity seen in membrane fractions isolated from these cells. Intracellular cyclic AMP concentrations were only elevated with glucagon. All ligands were capable of causing both desensitization/loss of glucagon-stimulated adenylate cyclase activity and stimulation of inositol phospholipid metabolism in the intact hepatocytes. Maximally effective doses of angiotensin precluded any further inhibition/desensitizing action when either glucagon or TH-glucagon was subsequently added to these intact cells, as has been shown previously for the phorbol ester TPA (12-O-tetradecanoylphorbol 13-acetate) [Heyworth, Wilson, Gawler & Houslay (1985) FEBS Lett. 187, 196-200]. Treatment of intact hepatocytes with these various ligands caused a selective loss of the glucagon-stimulated adenylate cyclase activity in a washed membrane fraction and did not alter the basal, GTP-, NaF- and forskolin-stimulated responses. Angiotensin failed to inhibit glucagon-stimulated adenylate cyclase activity when added directly to a washed membrane fraction from control cells. Glucagon GR2 receptor-stimulated adenylate cyclase is suggested to undergo desensitization/uncoupling through a cyclic AMP-independent process, which involves the stimulation of inositol phospholipid metabolism by glucagon acting through GR1 receptors. This action can be mimicked by other hormones which act on the liver to stimulate inositol phospholipid metabolism. As the phorbol ester TPA also mimics this process, it is proposed that protein kinase C activation plays a pivotal role in the molecular mechanism of desensitization of glucagon-stimulated adenylate cyclase. The site of the lesion in desensitization is shown to be at the level of coupling between the glucagon receptor and the stimulatory guanine nucleotide regulatory protein Gs, and it is suggested that one or both of these components may provide a target for phosphorylation by protein kinase C.
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256
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Zawalich WS, Diaz VA. Asperlicin antagonizes stimulatory effects of cholecystokinin on isolated islets. THE AMERICAN JOURNAL OF PHYSIOLOGY 1987; 252:E370-4. [PMID: 3548432 DOI: 10.1152/ajpendo.1987.252.3.e370] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Asperlicin, a product derived from the fungus Aspergillus alliaceus, antagonized the multiple stimulatory effects of cholecystokinin (CCK-8S) on isolated islets. At a level of 10 microM, asperlicin completely inhibited insulin release in response to 25 nM CCK-8S. Increasing the level of CCK-8S to 100 nM partially restored a secretory response, while an even greater insulin stimulatory effect was noted with 500 nM CCK-8S. The inhibitory effect of asperlicin on CCK-8S-induced release was reversible. Asperlicin exposure had no effect on glucose or glyceraldehyde-induced secretion. Asperlicin reduced, in parallel with secretion, the increase in 3H efflux from [3H]inositol prelabeled islets usually noted with CCK-8S addition. Asperlicin did not influence the small glucose-stimulated increase in 3H efflux. The results support the notion that asperlicin is a specific and potent antagonist of the multiple stimulatory effects of CCK-8S on islet tissue.
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257
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Slivka S, Insel P. Alpha 1-adrenergic receptor-mediated phosphoinositide hydrolysis and prostaglandin E2 formation in Madin-Darby canine kidney cells. Possible parallel activation of phospholipase C and phospholipase A2. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)61333-x] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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258
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Häggblad J, Heilbronn E. Externally applied adenosine-5'-triphosphate causes inositol triphosphate accumulation in cultured chick myotubes. Neurosci Lett 1987; 74:199-204. [PMID: 3033552 DOI: 10.1016/0304-3940(87)90149-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In striated muscle, adenosine-5'-triphosphate (ATP) potentiates the responses to acetylcholine. The underlying biochemical events are unknown. Here we report that ATP, externally applied to chick myotubes, induces a rapid, dose-dependent accumulation of intracellular inositol triphosphate which is correlated with a decrease in phosphatidyl 4,5-bisphosphate. Adenosine-5'-diphosphate, adenosine-5'-monophosphate and adenosine are less potent while beta, gamma-imido ATP is equipotent motoneurons and/or skeletal muscle controls the activation of a polyphosphoinositide phosphodiesterase via a cell membrane P2-purinoceptor, thus modulating skeletal muscle responses to transmitter release.
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259
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Altin JG, Bygrave FL. The influx of Ca2+ induced by the administration of glucagon and Ca2+-mobilizing agents to the perfused rat liver could involve at least two separate pathways. Biochem J 1987; 242:43-50. [PMID: 3496082 PMCID: PMC1147661 DOI: 10.1042/bj2420043] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The Ca2+-mobilizing actions of ADP, ATP and epidermal growth factor (EGF) and their interaction with glucagon were studied in a perfused liver system incorporating a Ca2+-selective electrode. ADP (1-100 microM), ATP (1-100 microM) and EGF (10-50 nM) all induced a net efflux, followed by a net uptake of Ca2+ in the intact liver. The co-administration of glucagon (or of cyclic AMP) with these agents resulted in a synergistic potentiation of the Ca2+ uptake response in a way which resembles the synergism observed when glucagon is administered with phenylephrine, vasopressin or angiotensin [Altin & Bygrave (1986) Biochem J. 238, 653-661]. The inability of diltiazem, verapamil and nifedipine to inhibit the Ca2+-influx response suggests that the stimulation of Ca2+ influx does not occur through voltage-sensitive Ca2+ channels. By contrast, the synergistic effects of glucagon in the stimulation of Ca2+ influx are inhibited by 10 mM-neomycin, and a lowering of the extracellular pH to 6.8. Simultaneous measurements of perfusate Ca2+ and pH changes suggest that the Ca2+ influx response is not mediated by a Ca2+/H+ exchange. The inability of neomycin and low extracellular pH to inhibit the refilling of the hormone-sensitive pool of Ca2+, after the administration of Ca2+-mobilizing agents alone, provides evidence for the existence in liver of at least two Ca2+-influx pathways, or mechanisms for regulating Ca2+ influx.
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260
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Whipps DE, Armston AE, Pryor HJ, Halestrap AP. Effects of glucagon and Ca2+ on the metabolism of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate in isolated rat hepatocytes and plasma membranes. Biochem J 1987; 241:835-45. [PMID: 3036077 PMCID: PMC1147637 DOI: 10.1042/bj2410835] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Rat hepatocytes whose phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) had been labelled for 60 min with 32P were treated with glucagon for 10 min or phenylephrine for 2 min. Glucagon caused a 20% increase in PIP but no change in PIP2 whereas phenylephrine caused a similar increase in PIP but a 15% decrease in PIP2. Addition of both hormones together for 10 min produced a 40% increase in PIP. A crude liver mitochondrial fraction incubated with [32P]Pi and ADP incorporated label into PIP, PIP2 and phosphatidic acid. The PIP2 was shown to be in contaminating plasma membranes and PIP in both lysosomal and plasma-membrane contamination. A minor but definitely mitochondrial phospholipid, more polar than PIP2, was shown to be labelled with 32P both in vitro and in hepatocytes. The rate of 32P incorporation into PIP was faster in mitochondrial/plasma-membrane preparations from rats treated with glucagon or if 3 microM-Ca2+ and Ruthenium Red were present in the incubation buffer. Loss of 32P from membranes labelled in vitro was shown to be accompanied by formation of inositol 1,4,5-trisphosphate (IP3) and inositol 1,4-bisphosphate, and was faster in preparations from glucagon-treated rats or in the presence of 3 microM-Ca2+. It is concluded that glucagon stimulates both PIP2 phosphodiesterase and phosphatidylinositol kinase activities, as does the presence of 3 microM-Ca2+. The resulting formation of IP3 may be responsible for the observed release of intracellular Ca2+ stores. The roles of a guanine nucleotide regulatory protein and phosphorylation in mediating these effects are discussed.
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261
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Woods NM, Cuthbertson KS, Cobbold PH. Agonist-induced oscillations in cytoplasmic free calcium concentration in single rat hepatocytes. Cell Calcium 1987; 8:79-100. [PMID: 3829123 DOI: 10.1016/0143-4160(87)90038-8] [Citation(s) in RCA: 243] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The effects of the alpha 1-adrenergic agonist phenylephrine and the peptide hormones angiotensin II and arg8-vasopressin on cytoplasmic free calcium concentration were investigated in single rat hepatocytes microinjected with the photoprotein aequorin. Hepatocytes responded to physiological concentrations of the glycogenolytic agonists with a series of repetitive Ca transients. In each transient free Ca rose in 2-3s to above 600 nM from a resting level of 200 nM. Transient duration depended on the agonist and ranged from approximately 7s for phenylephrine to approximately 15s for angiotensin. Transient frequency, but not shape or size, depended on agonist concentration. The period ranged from less than 20s to several minutes. We suggest that the frequency of the Ca transients is the principal determinant of the amplitude of the cellular response to calcium-mobilizing agonists.
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262
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Rettenmier CW, Jackowski S, Rock CO, Roussel MF, Sherr CJ. Transformation by the v-fms oncogene product: an analog of the CSF-1 receptor. J Cell Biochem 1987; 33:109-15. [PMID: 3032997 DOI: 10.1002/jcb.240330205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The product of the c-fms proto-oncogene is related to, and possibly identical with, the receptor for the macrophage colony-stimulating factor, M-CSF (CSF-1). Unlike the product of the v-erbB oncogene, which is a truncated version of the EGF receptor, the glycoprotein encoded by the v-fms oncogene retains an intact extracellular ligand-binding domain so that cells transformed by v-fms express CSF-1 receptors at their surface. Although fibroblasts susceptible to transformation by v-fms generally produce CSF-1, v-fms-mediated transformation does not depend on an exogenous source of the growth factor, and neutralizing antibodies to CSF-1 do not affect the transformed phenotype. An alteration of the v-fms gene product at its extreme carboxyl-terminus represents the major structural difference between it and the c-fms-coded glycoprotein and may affect the tyrosine kinase activity of the v-fms-coded receptor. Consistent with this interpretation, tyrosine phosphorylation of the v-fms products in membranes was observed in the absence of CSF-1 and was not enhanced by addition of the murine growth factor. Cells transformed by v-fms have a constitutively elevated specific activity of a guanine nucleotide-dependent, phosphatidylinositol-4,5-diphosphate-specific phospholipase C. We speculate that the tyrosine kinase activity of the v-fms/c-fms gene products may be coupled to this phospholipase C, possibly through a G regulatory protein, thereby increasing phosphatidylinositol turnover and generating the intracellular second messengers diacylglycerol and inositol triphosphate.
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263
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Rincon M, Boss WF. myo-Inositol Trisphosphate Mobilizes Calcium from Fusogenic Carrot (Daucus carota L.) Protoplasts. PLANT PHYSIOLOGY 1987; 83:395-8. [PMID: 16665256 PMCID: PMC1056368 DOI: 10.1104/pp.83.2.395] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
To determine whether or not inositol trisphosphate (IP(3)) mobilizes calcium in higher plant cells, we investigated the effect of IP(3) on Ca(2+) fluxes in fusogenic carrot (Daucus carota L.) protoplasts. The protoplasts were incubated in (45)Ca(2+)-containing medium and the (45)Ca(2+) associated with the protoplasts was monitored with time. Addition of IP(3) (20 micromolar) caused a 17% net loss of the accumulated (45)Ca(2+) within 4 minutes. There was a reuptake of (45)Ca(2+) and the protoplasts recovered to their initial value by 10 minutes. Phytic acid (IP(6)), also stimulated (45)Ca(2+) efflux from the protoplasts. Both the IP(3(-) ) and the IP(6(-) )induced (45)Ca(2+) efflux were inhibited by the calmodulin antagonist, trifluoperazine.
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Affiliation(s)
- M Rincon
- Department of Botany, North Carolina State University, Raleigh, North Carolina 27695
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264
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Cockcroft S, Taylor JA. Fluoroaluminates mimic guanosine 5'-[gamma-thio]triphosphate in activating the polyphosphoinositide phosphodiesterase of hepatocyte membranes. Role for the guanine nucleotide regulatory protein Gp in signal transduction. Biochem J 1987; 241:409-14. [PMID: 3036062 PMCID: PMC1147575 DOI: 10.1042/bj2410409] [Citation(s) in RCA: 96] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Fluoride and guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) both activate the hepatocyte membrane polyphosphoinositide phosphodiesterase (PPI-pde) in a concentration-dependent manner. AlCl3 enhances the fluoride effect, supporting the concept that [A1F4]- is the active species. Analysis of the products of inositol lipid hydrolysis demonstrate that phosphatidylinositol bisphosphate is the major lipid to be hydrolysed. Guanosine 5'-[beta-thio]diphosphate (GDP beta S) is an inhibitor of activation of PPI-pde by both fluoride and GTP gamma S. These observations suggest that the guanine nucleotide regulatory protein (termed Gp) bears a structural resemblance to the well-characterized G-proteins of the adenylate cyclase system and the cyclic GMP phosphodiesterase system in phototransduction.
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265
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Shin S, Fujiwara Y, Wada A, Takama T, Orita Y, Kamada T, Tagawa K. Angiotensin II-induced increase in inositol 1,4,5-trisphosphate in cultured rat mesangial cells: evidence by refined high performance liquid chromatography. Biochem Biophys Res Commun 1987; 142:70-7. [PMID: 3493002 DOI: 10.1016/0006-291x(87)90452-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Angiotensin II-induced change in inositol phosphates were studied in cultured rat mesangial cells prelabeled with [3H]myo-inositol. By using anion-exchange high performance liquid chromatography, we could analyzed the change in inositol mono-, bis-, and tris-phosphate more rapidly and easily with higher resolution than the previously reported methods. Angiotensin II rapidly increased inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate within 15 sec, followed by an increase in inositol 1-monophosphate at 30 sec. Angiotensin II-induced increases in inositol phosphates were dose-dependent and completely blocked by saralasin. These results indicate that angiotensin II induces the production of inositol phosphates including inositol 1,4,5-trisphosphate, an intracellular Ca2+-releasing factor, in cultured rat mesangial cells.
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266
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Nelemans A, Den Hertog A. Changes in membrane potential and phosphoinositides during alpha 1-adrenoceptor stimulation in smooth muscle cells of guinea-pig taenia caeci. Eur J Pharmacol 1987; 133:215-23. [PMID: 2880739 DOI: 10.1016/0014-2999(87)90153-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effect of a submaximal concentration of adrenaline (3-5 microM) was studied in taenia caeci smooth muscle cells. Membrane potential hyperpolarization was observed in intact muscle preparations and this response could be separated into two phases, depending on the state of a membrane-bound calcium compartment. The effect of alpha 1-adrenergic stimulation was also measured by [3H]inositol incorporation into phospholipid and inositol phosphate fractions of taenia cell suspensions both in the absence and presence of 2.5 mM extracellular calcium. In the absence of extracellular calcium the inositol phospholipids increased within 15 s after stimulation, followed by enhanced inositol phosphates. With calcium present there was a biphasic increase in the phosphatidylinositol 4,5-bisphosphate (PIP2) fraction with a simultaneous release of inositol phosphates. Lithium ions affected the incorporation of label into the lipids but not into the inositol phosphate fractions. These findings suggest that, in taenia caeci cells, alpha 1-adrenergic-induced membrane hyperpolarization resulting in muscle relaxation is associated with changes in the PIP2 content.
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267
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Wakelam MJ, Patterson S, Hanley MR. L6 skeletal muscle cells have functional V1-vasopressin receptors coupled to stimulated inositol phospholipid metabolism. FEBS Lett 1987; 210:181-4. [PMID: 2947815 DOI: 10.1016/0014-5793(87)81333-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effects of vasopressin and related peptides upon the rat skeletal muscle cell line, L6, have been examined. No effects upon cellular cyclic AMP levels were found indicating that L6 cells possess no functional V2-vasopressin receptors. Vasopressin and its analogues did, however, stimulate the rapid and dose-dependent accumulation of inositol phosphates. This effect and the rank order of potency of vasopressin analogues demonstrate the presence of functional V1-vasopressin receptors upon L6 cells. These results suggest that the L6 line may be a useful model for vasopressin effects upon skeletal muscle metabolism.
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268
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Exton JH. Mechanisms of hormonal regulation of hepatic glucose metabolism. DIABETES/METABOLISM REVIEWS 1987; 3:163-83. [PMID: 3032541 DOI: 10.1002/dmr.5610030108] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Acute hormonal regulation of liver carbohydrate metabolism mainly involves changes in the cytosolic levels of cAMP and Ca2+. Epinephrine, acting through beta 2-adrenergic receptors, and glucagon activate adenylate cyclase in the liver plasma membrane through a mechanism involving a guanine nucleotide-binding protein that is stimulatory to the enzyme. The resulting accumulation of cAMP leads to activation of cAMP-dependent protein kinase, which, in turn, phosphorylates many intracellular enzymes involved in the regulation of glycogen metabolism, gluconeogenesis, and glycolysis. These are (1) phosphorylase b kinase, which is activated and, in turn, phosphorylates and activates phosphorylase, the rate-limiting enzyme for glycogen breakdown; (2) glycogen synthase, which is inactivated and is rate-controlling for glycogen synthesis; (3) pyruvate kinase, which is inactivated and is an important regulatory enzyme for glycolysis; and (4) the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase bifunctional enzyme, phosphorylation of which leads to decreased formation of fructose 2,6-P2, which is an activator of 6-phosphofructo-1-kinase and an inhibitor of fructose 1,6-bisphosphatase, both of which are important regulatory enzymes for glycolysis and gluconeogenesis. In addition to rapid effects of glucagon and beta-adrenergic agonists to increase hepatic glucose output by stimulating glycogenolysis and gluconeogenesis and inhibiting glycogen synthesis and glycolysis, these agents produce longer-term stimulatory effects on gluconeogenesis through altered synthesis of certain enzymes of gluconeogenesis/glycolysis and amino acid metabolism. For example, P-enolpyruvate carboxykinase is induced through an effect at the level of transcription mediated by cAMP-dependent protein kinase. Tyrosine amino-transferase, serine dehydratase, tryptophan oxygenase, and glucokinase are also regulated by cAMP, in part at the level of specific messenger RNA synthesis. The sympathetic nervous system and its neurohumoral agonists epinephrine and norepinephrine also rapidly alter hepatic glycogen metabolism and gluconeogenesis acting through alpha 1-adrenergic receptors. The primary response to these agonists is the phosphodiesterase-mediated breakdown of the plasma membrane polyphosphoinositide phosphatidylinositol 4,5-P2 to inositol 1,4,5-P3 and 1,2-diacylglycerol. This involves a guanine nucleotide-binding protein that is different from those involved in the regulation of adenylate cyclase. Inositol 1,4,5-P3 acts as an intracellular messenger for Ca2+ mobilization by releasing Ca2+ from the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 400 WORDS)
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269
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van de Werve G, Jeanrenaud B. Liver glycogen metabolism: an overview. DIABETES/METABOLISM REVIEWS 1987; 3:47-78. [PMID: 3032542 DOI: 10.1002/dmr.5610030104] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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270
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Conn PM, Huckle WR, Andrews WV, McArdle CA. The molecular mechanism of action of gonadotropin releasing hormone (GnRH) in the pituitary. RECENT PROGRESS IN HORMONE RESEARCH 1987; 43:29-68. [PMID: 2819996 DOI: 10.1016/b978-0-12-571143-2.50007-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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271
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Morgan RO, Chang JP, Catt KJ. Novel aspects of gonadotropin-releasing hormone action on inositol polyphosphate metabolism in cultured pituitary gonadotrophs. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(19)75766-4] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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272
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Andrews WV, Conn PM. Measurement of inositol phospholipid metabolites by one-dimensional thin-layer chromatography. Methods Enzymol 1987; 141:156-68. [PMID: 3037243 DOI: 10.1016/0076-6879(87)41064-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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273
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Guillemette G, Balla T, Baukal AJ, Spät A, Catt KJ. Intracellular receptors for inositol 1,4,5-trisphosphate in angiotensin II target tissues. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(19)75741-x] [Citation(s) in RCA: 117] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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274
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Berta P, Seguin J, Vidal N, Haiech J, Mathieu MN, Chevillard C. Influence of Ca2+e on 5-HT2- and alpha 1-induced arterial contraction and phosphoinositide metabolism. Eur J Pharmacol 1986; 132:253-7. [PMID: 3028839 DOI: 10.1016/0014-2999(86)90612-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Serotonin and phenylephrine were found to induce contractile responses and inositol phosphate (IP) formation in isolated rat tail artery. Both processes displayed similar concentration dependence in the presence of 2.5 mM external calcium (Ca2+e) and both were respectively inhibited by either ketanserine or prazosin, depending on the agonist used. In the absence of Ca2+e the amines no longer produced a contractile effect. In addition, lack of Ca2+ caused a shift to the right in the dose-response curve for phenylephrine-induced IP formation whereas serotonin-induced IP formation was not affected by changes in Ca2+e. The results suggest that alpha 1- and 5-HT2-induced contractions are quantitatively related to phosphatidylinositol metabolism. Contraction, but not IP formation requires the presence of Ca2+e. Different effects of Ca2+e on phenylephrine- and serotonin-induced IP formation could be related to a differential Ca2+ effect on binding of alpha 1- or 5-HT2 agonists.
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275
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Lundberg GA, Jergil B, Sundler R. Phosphatidylinositol-4-phosphate kinase from rat brain. Activation by polyamines and inhibition by phosphatidylinositol 4,5-bisphosphate. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 161:257-62. [PMID: 3023090 DOI: 10.1111/j.1432-1033.1986.tb10441.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Phosphatidylinositol-4-phosphate (PtdIns-P) kinase was purified approximately 30-fold from rat brain cytosol. No contaminating activity of PtdIns kinase or of phosphomonoesterase and phospholipase C using PtdIns-P or PtdIns-P2 as substrate could be detected in the enzyme preparation. The PtdIns-P kinase activity was severalfold higher when PtdIns-P/PtdEtn vesicles rather than PtdIns-P alone were used as substrate. This might be due to increased accessibility of the enzyme for the vesicular substrate, further indicated by the lower activity obtained when PtdCho or PtdIns, phospholipids with bulky head groups, was also present in the vesicles. The product PtdIns-P2 was a competitive inhibitor with respect to PtdIns-P and 50% inhibition of enzyme activity was observed at the same product concentration regardless of whether the substrate-product mixture was presented in vesicular or micellar form, or the substrate and product were added in separate vesicles. The polyamines spermine and spermidine enhanced PtdIns-P kinase activity severalfold. Spermine also caused a shift in the MgCl2 saturation curve from sigmoidal to hyperbolic, lowering the Mg2+ concentration required for optimum kinase activity to the physiological range. Myelin basic protein enhanced the enzyme activity when PtdIns-P/PtdEtn vesicles were used as substrate, whereas it was inhibitory when PtdIns-P was added alone. The possible role of polyamines and the product PtdIns-P2 in the regulation of PtdIns-P kinase activity is discussed.
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276
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Fahrenholz F, Kojro E, Müller M, Boer R, Löhr R, Grzonka Z. Iodinated photoreactive vasopressin antagonists: labelling of hepatic vasopressin receptor subunits. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 161:321-8. [PMID: 2946581 DOI: 10.1111/j.1432-1033.1986.tb10450.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
To identify and characterize V1 vasopressin receptors, photoreactive antagonists of the glycogenolytic and vasoconstrictor activity of vasopressin have been synthesized. The following analogues with 3-mercapto-3,3-cyclopentamethylene-propionic acid (Mca) and N-methylalanine (MeAla) in position 1 and 7 of vasopressin (VP) were effective V1 antagonists: [Mca1, D-Tyr2, MeAla7, Lys8]VP (1), [Mca1, MeAla7, Arg8, Lys9]VP (2), [Mca1, MeAla7, Arg8, D-Lys9]VP (3). Introduction of the photoreactive 4-azidophenylamidino group into the side-chain of Lys8 in analogue 1 or into Lys9 in analogues 2 and 3 increased the potency (for analogue 1 a tenfold increase in the antiglycogenolytic effect and a fivefold increase in the antivasopressor effect) and binding affinity for the rat hepatic V1 receptor. Mono-iodination at Tyr2 with 125I resulted in photoreactive antagonists of high specific radioactivity, which had roughly the same binding affinity as vasopressin for the rat hepatic V1 receptor (Kd = 0.9-1.8 nM). In photoaffinity labelling experiments with purified rat liver membranes, containing 2--3 pmol V1 receptor/mg protein, the analogues labelled specifically two proteins with the relative molecular masses (Mr) of 30,000 and 38,000. These results and the results of a recent study using 3H-labelled photoreactive vasopressin agonists [Boer, R. and Fahrenholz, F. (1985) J. Biol. Chem. 260, 15051-15054] provide evidence that both vasopressin agonists and antagonists can interact with the same two subunits of the heterodimeric hepatic V1 receptor. Furthermore the radioiodinated photoreactive V1 antagonists should be helpful to identify V1 receptor proteins in membranes of other cell types.
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Kirk CJ, Guillon G, Balestre MN, Jard S. Stimulation, by vasopressin and other agonists, of inositol-lipid breakdown and inositol phosphate accumulation in WRK 1 cells. Biochem J 1986; 240:197-204. [PMID: 3827839 PMCID: PMC1147393 DOI: 10.1042/bj2400197] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
WRK 1 cells were labelled to equilibrium with 2-myo-[3H]inositol and stimulated with vasopressin. Within 3 s of hormone stimulation there was a marked accumulation of 3H-labelled InsP2 and InsP3 (inositol bis- and tris-phosphate), but not of InsP (inositol monophosphate). There was an associated, and rapid, depletion of 3H-labelled PtdInsP and PtdInsP2 (phosphatidylinositol mono- and bis-phosphates), but not of PtdIns (phosphatidylinositol), in these cells. Some 4% of the radioactivity in the total inositol lipid pool of WRK 1 cells was recovered in InsP2 and InsP3 after 10 s stimulation with the hormone. The selectivity of the vasopressin receptors of WRK 1 cells for a variety of vasopressin agonists and antagonists revealed these to be of the V1a subtype. There was no receptor reserve for vasopressin-stimulated inositol phosphate accumulation in WRK 1 cells. The accumulation of inositol phosphates was enhanced in the presence of Li+ions. Half-maximal accumulation of InsP, InsP2 and InsP3 in vasopressin-stimulated cells was observed with 0.9, 3.0 and 3.6 mM-Li+ respectively. Bradykinin and 5-hydroxytryptamine also provoked inositol phosphate accumulation in WRK 1 cells. The effects of sub-optimal concentrations of bradykinin and vasopressin upon inositol phosphate accumulation were additive, but those of optimal concentrations of the hormones were not.
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278
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Enyedi P, Mucsi I, Hunyady L, Catt KJ, Spät A. The role of guanyl nucleotide binding proteins in the formation of inositol phosphates in adrenal glomerulosa cells. Biochem Biophys Res Commun 1986; 140:941-7. [PMID: 3096331 DOI: 10.1016/0006-291x(86)90726-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A non-hydrolysable GTP analogue enhanced the formation of [3H]inositol polyphosphates in permeabilized adrenal glomerulosa cells. Pertussis toxin, which ADP-ribosylated Ni, failed to influence angiotensin-induced formation of 3H-labelled inositol phosphates and the incorporation of [32F]phosphate into phosphatidylinositol and phosphatidic acid. These results show that Ni is present and a G-protein activates phospholipase C also in glomerulosa cells, however, it is not Ni which couples angiotensin receptors to the enzyme.
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279
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Hallam TJ, Pearson JD. Exogenous ATP raises cytoplasmic free calcium in fura-2 loaded piglet aortic endothelial cells. FEBS Lett 1986; 207:95-9. [PMID: 3533627 DOI: 10.1016/0014-5793(86)80019-9] [Citation(s) in RCA: 165] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cultured piglet endothelial cells were grown to confluence on glass coverslips and loaded with the fluorescent Ca2+ indicator, fura-2. Using a dual-wavelength excitation fluorescence spectrophotometer it was found that ATP caused a rapid transient elevation in [Ca2+]i in the presence of extracellular calcium which decreased to a maintained elevated level. With no extracellular calcium ATP evoked a similar transient increase which returned to the basal level. Addition of 50 mM K+ had no effect on [Ca2+]i or on the effect of ATP on [Ca2+]i in the presence of extracellular Ca2+. The data suggest that ATP causes both discharge of calcium from an intracellular pool and influx across the plasma membrane although this is unlikely to be via a voltage-operated channel. ATP stimulated simultaneously the production of PGI2 to a similar extent in the presence or absence of extracellular calcium. Elevated [Ca2+]i may be an important activation pathway in the endothelial cell.
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280
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Poggioli J, Sulpice JC, Vassort G. Inositol phosphate production following alpha 1-adrenergic, muscarinic or electrical stimulation in isolated rat heart. FEBS Lett 1986; 206:292-8. [PMID: 3019774 DOI: 10.1016/0014-5793(86)80999-1] [Citation(s) in RCA: 106] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A possible participation of polyphosphoinositide metabolism in the excitation-contraction coupling in heart was investigated. Isolated rat ventricles prelabelled with myo-[2-3H]inositol were stimulated by conditions that increase mechanical activity. Both noradrenaline and carbachol increased the basal level of IP3, IP2 and IP by the activation of alpha 1-adrenergic and muscarinic receptors, respectively. Electrical stimulation accelerated inositol lipid degradation by phospholipase C thus enhancing the IP3 level as compared to quiescent ventricles. It is proposed that IP3 may be involved in excitation-contraction coupling in cardiac tissue.
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MESH Headings
- Animals
- Carbachol/pharmacology
- Chromatography, High Pressure Liquid
- Electric Stimulation
- Female
- Inositol 1,4,5-Trisphosphate
- Inositol Phosphates/biosynthesis
- Myocardial Contraction
- Myocardium/metabolism
- Norepinephrine/pharmacology
- Rats
- Rats, Inbred Strains
- Receptors, Adrenergic, alpha/drug effects
- Receptors, Adrenergic, alpha/physiology
- Receptors, Muscarinic/drug effects
- Receptors, Muscarinic/physiology
- Sugar Phosphates/biosynthesis
- Type C Phospholipases/metabolism
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Hughes BP, Milton SE, Barritt GJ. Effects of vasopressin and La3+ on plasma-membrane Ca2+ inflow and Ca2+ disposition in isolated hepatocytes. Evidence that vasopressin inhibits Ca2+ disposition. Biochem J 1986; 238:793-800. [PMID: 3099775 PMCID: PMC1147206 DOI: 10.1042/bj2380793] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Vasopressin caused a 40% inhibition of 45Ca uptake after the addition of 0.1 mM-45Ca2+ to Ca2+-deprived hepatocytes. At 1.3 mM-45Ca2+, vasopressin and ionophore A23187 each caused a 10% inhibition of 45Ca2+ uptake, whereas La3+ increased the rate of 45Ca2+ uptake by Ca2+-deprived cells. Under steady-state conditions at 1.3 mM extracellular Ca2+ (Ca2+o), vasopressin and La3+ each increased the rate of 45Ca2+ exchange. The concentrations of vasopressin that gave half-maximal stimulation of 45Ca2+ exchange and glycogen phosphorylase activity were similar. At 0.1 mM-Ca2+o, La3+ increased, but vasopressin did not alter, the rate of 45Ca2+ exchange. The results of experiments performed with EGTA or A23187 or by subcellular fractionation indicate that the Ca2+ taken up by hepatocytes in the presence of La3+ is located within the cell. The addition of 1.3 mM-Ca2+o to Ca2+-deprived cells caused increases of approx. 50% in the concentration of free Ca2+ in the cytoplasm [( Ca2+]i) and in glycogen phosphorylase activity. Much larger increases in these parameters were observed in the presence of vasopressin or ionophore A23187. In contrast with vasopressin, La3+ did not cause a detectable increase in glycogen phosphorylase activity or in [Ca2+]i. It is concluded that an increase in plasma membrane Ca2+ inflow does not by itself increase [Ca2+]i, and hence that the ability of vasopressin to maintain increased [Ca2+]i over a period of time is dependent on inhibition of the intracellular removal of Ca2+.
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283
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Altin JG, Bygrave FL. Synergistic stimulation of Ca2+ uptake by glucagon and Ca2+-mobilizing hormones in the perfused rat liver. A role for mitochondria in long-term Ca2+ homoeostasis. Biochem J 1986; 238:653-61. [PMID: 3026358 PMCID: PMC1147188 DOI: 10.1042/bj2380653] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A perfused liver system incorporating a Ca2+-sensitive electrode was used to study the long-term effects of glucagon and cyclic AMP on the mobilization of Ca2+ induced by phenylephrine, vasopressin and angiotensin. At 1.3 mM extracellular Ca2+ the co-administration of glucagon (10 nM) or cyclic AMP (0.2 mM) and a Ca2+-mobilizing hormone led to a synergistic potentiation of Ca2+ uptake by the liver, to a degree which was dependent on the order of hormone administration. A maximum net amount of Ca2+ influx, corresponding to approx. 3800 nmol/g of liver (the maximum rate of influx was 400 nmol/min per g of liver), was induced when cyclic AMP or glucagon was administered about 4 min before vasopressin and angiotensin. These changes are over an order of magnitude greater than those induced by Ca2+-mobilizing hormones alone [Altin & Bygrave (1985) Biochem. J. 232, 911-917]. For a maximal response the influx of Ca2+ was transient and was essentially complete after about 20 min. Removal of the hormones was followed by a gradual efflux of Ca2+ from the liver over a period of 30-50 min; thereafter, a similar response could be obtained by a second administration of hormones. Dose-response measurements indicate that the potentiation of Ca2+ influx by glucagon occurs even at low (physiological) concentrations of the hormone. By comparison with phenylephrine, the stimulation of Ca2+ influx by vasopressin and angiotensin is more sensitive to low concentrations of glucagon and cyclic AMP, and can be correlated with a 20-50-fold increase in the calcium content of mitochondria. The reversible uptake of such large quantities of Ca2+ implicates the mitochondria in long-term cellular Ca2+ regulation.
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284
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Barrett PQ, Kojima I, Kojima K, Zawalich K, Isales CM, Rasmussen H. Temporal patterns of protein phosphorylation after angiotensin II, A23187 and/or 12-O-tetradecanoylphorbol 13-acetate in adrenal glomerulosa cells. Biochem J 1986; 238:893-903. [PMID: 3099777 PMCID: PMC1147219 DOI: 10.1042/bj2380893] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The temporal patterns of protein phosphorylation in the adrenal glomerulosa cell were analysed by two-dimensional electrophoresis after stimulation with 10 nM-angiotensin II or various agents [10 nM-12-O-tetradecanoylphorbol 13-acetate (TPA), 50 nM-A23187, 1 microM-nitrendipine], administered singly or in combination. These patterns were compared with the temporal patterns of aldosterone secretion induced by the same agonists and antagonists. After 1 and 30 min of stimulation with angiotensin II, different patterns of protein phosphorylation were observed. A comparison of these patterns reveals that: the phosphorylation of only one protein was persistently enhanced during the continuous incubation with angiotensin II; the phosphorylation of five proteins was transiently enhanced (at 1 min but not 30 min); and the phosphorylation of three proteins did not occur at 1 min but was seen at 30 min. Addition of the phorbol ester TPA alone, which at 30 min is without effect in enhancing aldosterone production, has no effect on protein phosphorylation. The combined addition of TPA and the Ca2+ ionophore, A23187, which, like angiotensin II, evokes a sustained increase in aldosterone production, reproduced the temporal patterns of protein phosphorylation seen after angiotensin II action. Manipulations (A23187 alone, angiotensin II plus nitrendipine) which evoke only a transient rise in aldosterone production rate induce a transient rise in cellular protein phosphorylation. The 1 min patterns of phosphorylation seen after A23187 or combined angiotensin II and nitrendipine (a Ca2+ channel antagonist) are similar to those observed after 1 min of angiotensin II stimulation. These results suggest that, when angiotensin II acts, the initial cellular response is mediated by a different mechanism than that responsible for the sustained response.
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285
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Best L. A role for calcium in the breakdown of inositol phospholipids in intact and digitonin-permeabilized pancreatic islets. Biochem J 1986; 238:773-9. [PMID: 3541917 PMCID: PMC1147203 DOI: 10.1042/bj2380773] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Glucose (20 mM) and 4-methyl-2-oxopentanoate (10 mM) both caused a pronounced stimulation of insulin release and of [3H]inositol phosphate production in rat pancreatic islets prelabelled with myo-[3H]inositol. Secretory responses to these nutrients were markedly impaired by lowering the Ca2+ concentration of the incubation medium to 10(-4)M or less, whereas stimulated inositol phosphate production was sensitive to Ca2+ within the range 10(-6)-10(-4)M. Inositol phosphate formation in response to carbamoylcholine was also found to be dependent on the presence of 10(-5)M-Ca2+ or above. Raising the concentration of K+ in the medium resulted in a progressive, Ca2+-dependent stimulation of inositol phosphate production in islets, although no significant stimulation of insulin release was observed. In islets prelabelled with myo[3H]inositol, then permeabilized by exposure to digitonin, [3H]inositol phosphate production could be triggered by raising the Ca2+ concentration from 10(-7) to 10(-5)M. This effect was dependent on the concentration of ATP and the presence of Li+, and involved detectable increases in the levels of InsP3 and InsP2 as well as InsP. A potentiation of inositol phosphate production by carbamoylcholine was observed in permeabilized islets at lower Ca2+ concentrations, although nutrient stimuli were ineffective. No significant effects were observed with guanine nucleotides or with neomycin, although NADH produced a modest increase and adriamycin a small inhibition of inositol phosphate production in permeabilized islets. These results strongly suggest that Ca2+ ions play an important role in the stimulation of inositol lipid metabolism in islets in response to nutrient secretagogues, and that inositide breakdown may actually be triggered by Ca2+ entry into the islet cells.
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286
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Vaartjes WJ, Bijleveld C, Geelen MJ, van den Bergh SG. No synergism between ionomycin and phorbol ester in fatty acid synthesis by isolated rat hepatocytes. Biochem Biophys Res Commun 1986; 139:403-9. [PMID: 2876702 DOI: 10.1016/s0006-291x(86)80005-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
With hepatocytes in suspension, freshly isolated from meal-fed rats, no significant effect of ionomycin on the rate of de novo fatty acid synthesis was observed, whereas phorbol myristate acetate (PMA) was strongly stimulatory. The combination of ionomycin and PMA produced the same stimulation as was seen with PMA alone. Stimulation of fatty acid synthesis by vasopressin was comparable and not additive to that observed with PMA, indicating that activation of protein kinase C is solely responsible for this metabolic effect of vasopressin. Both vasopressin and PMA increased acetyl-CoA carboxylase activity in isolated rat hepatocytes.
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287
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288
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Wakelam MJ, Murphy GJ, Hruby VJ, Houslay MD. Activation of two signal-transduction systems in hepatocytes by glucagon. Nature 1986; 323:68-71. [PMID: 3018586 DOI: 10.1038/323068a0] [Citation(s) in RCA: 321] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The ability of glucagon to stimulate glycogen breakdown in liver played a key part in the classic identification of cyclic AMP and hormonally stimulated adenylate cyclase. But several observations indicate that glucagon can exert effects independent of elevating intracellular cAMP concentrations. These effects are probably mediated by an elevation of the intracellular concentration of free Ca2+ although the mechanism by which this occurs is unknown. We show here that glucagon, at the low concentrations found physiologically, causes both a breakdown of inositol phospholipids and the production of inositol phosphates. Indeed, we show that the glucagon analogue, (1-N-alpha-trinitrophenylhistidine,12-homoarginine)glucagon (TH-glucagon), which does not activate adenylate cyclase or cause any increase in cAMP in hepatocytes yet can fully stimulate glycogenolysis, gluconeogenesis and urea synthesis, stimulates the production of inositol phosphates. This stimulation of inositol phospholipid metabolism by low concentrations of glucagon provides a mechanism whereby glucagon can exert cAMP-independent actions on target cells. We suggest that hepatocytes possess two distinct receptors for glucagon, a GR-1 receptor coupled to stimulate inositol phospholipid breakdown and a GR-2 receptor coupled to stimulate adenylate cyclase activity.
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289
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Court JA, Fowler CJ, Candy JM, Hoban PR, Smith CJ. Raising the ambient potassium ion concentration enhances carbachol stimulated phosphoinositide hydrolysis in rat brain hippocampal and cerebral cortical miniprisms. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1986; 334:10-6. [PMID: 3024020 DOI: 10.1007/bf00498734] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The influence of the ambient potassium ion concentration ([K+]) upon agonist stimulated hydrolysis of phosphoinositides (PI) has been studied in isolated miniprisms of rat hippocampus and cerebral cortex. When the external [K+] was raised from 6 to 18 mmol/l, there was little or no increase in the hydrolysis of PI in the absence of agonist, however, carbachol (100 mumol/l) stimulated hydrolysis was greatly enhanced in both brain regions studied. Thus, carbachol stimulated the hydrolysis of PI to 146% and 386% of control levels at potassium concentrations of 5.88 and 18.2 mmol/l, respectively, in the rat hippocampus. A similar enhancement of muscarine (100 mumol/l) stimulation was observed in cortical miniprisms with 18 mmol/l [K+]. A further enhancement was seen at higher ambient [K+], although basal hydrolysis of PI was then also increased. The carbachol-stimulated hydrolysis of PI found at both 6 and raised [K+] was prevented by atropine (1 and 10 mumol/l) and tetraethylammonium (20 mmol/l), but not by 10 mmol/l Mg2+. Pirenzepine (50 nmol/l) also reduced this response. The ions Cs+ and Rb+ (but not Li+ or Tris+) produced a similar enhancement of the carbachol stimulation to that found with K+. At a buffer [K+] of 6 mmol/l, noradrenaline (100 mumol/l) produced a 2-fold increase in the hydrolysis of PI whereas 5-hydroxytryptamine (100 mumol/l) and histamine (500 mumol/l) had little or no effect. However, histamine and 5-hydroxytryptamine did stimulate the hydrolysis of PI when [K+] was increased. Miniprism ATP content was not changed by a rise in [K+] to 18 mmol/l. The significance of these results is discussed in terms of the postsynaptic cellular events following cholinergic stimulation.
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290
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Leach RP, Shears SB, Kirk CJ, Titheradge MA. Changes in free cytosolic calcium and accumulation of inositol phosphates in isolated hepatocytes by [Leu]enkephalin. Biochem J 1986; 238:537-42. [PMID: 3800950 PMCID: PMC1147167 DOI: 10.1042/bj2380537] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Isolated hepatocytes from fed rats were used to study the effects of the opioid peptide [Leu]enkephalin on intracellular free cytosolic Ca2+ ([Ca2+]i) and inositol phosphate production. By measuring the fluorescence of the intracellular Ca2+-selective indicator quin-2, [Leu]enkephalin was found to increase [Ca2+]i rapidly from a resting value of 0.219 microM to 0.55 microM. The magnitude of this response was comparable with that produced by maximally stimulating concentrations of either vasopressin (100 nM) or phenylephrine (10 microM). The opioid-peptide-mediated increase in [Ca2+]i showed a dose-dependency comparable with the activation of phosphorylase, but it preceded the increase in phosphorylase alpha activity. Addition of [Leu]enkephalin to hepatocytes prelabelled with myo-[2-3H(n)]inositol resulted in a significant stimulation of inositol phosphate production. At 10 min after hormone addition, there were increases in the concentrations of inositol mono-, bis- and tris-phosphate fractions of 12-, 9- and 14-fold respectively. No effect was apparent on the glycerophosphoinositol fraction. The effect of 10 microM-[Leu]enkephalin on inositol phosphate production was significantly greater than that obtained with 10 microM-phenylephrine, but marginally smaller than that induced by 100 nM-vasopressin. However, at these concentrations all three agonists gave a comparable increase in [Ca2+]i and activation of phosphorylase a. These data provide evidence for [Leu]enkephalin acting via a mechanism involving a mobilization of Ca2+ as a result of increased phosphatidylinositol turnover.
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291
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Palmer S, Hawkins PT, Michell RH, Kirk CJ. The labelling of polyphosphoinositides with [32P]Pi and the accumulation of inositol phosphates in vasopressin-stimulated hepatocytes. Biochem J 1986; 238:491-9. [PMID: 3026353 PMCID: PMC1147161 DOI: 10.1042/bj2380491] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
When hepatocytes were incubated with [32P]Pi, the kinetics for the labelling of the monoester phosphate groups of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate were similar to each other and slightly slower than that for the labelling of the gamma-phosphate of ATP. Analysis of the water-soluble 3H-labelled materials derived from [3H]inositol-labelled hepatocytes revealed that, in addition to inositol and its mono-, bis- and tris-phosphates (Ins, InsP, InsP2 and InsP3), these cells contained two unidentified radioactive compounds which co-eluted with InsP on anion-exchange chromatography. When [3H]inositol-labelled hepatocytes were stimulated with 0.23 microM-vasopressin in the presence of 10 mM-Li+, there was an accumulation of radioactivity in InsP, InsP2 and InsP3 but not in Ins or the two unidentified compounds. Further analysis of these inositol phosphates by h.p.l.c. revealed that vasopressin also stimulates the accumulation of inositol tetrakisphosphate (InsP4) in these cells. Vasopressin-stimulated InsP and InsP2 accumulations were maximal in the presence of 1-10 mM-Li+ but InsP3 accumulation continued to increase up to 50 mM-Li+. Accumulated inositol phosphates were retained within the cell. Li+ from 1 to 50 mM did not influence the extent of vasopressin-stimulated inositol lipid degradation in hepatocytes. In the absence of Li+, radioactivity in vasopressin-stimulated hepatocytes accumulated almost entirely in free inositol. The vasopressin-stimulated accumulation of inositol phosphates in the presence of 10 mM-Li+ was abolished by a V1-vasopressin antagonist. Inositol phosphate accumulation was not influenced by ionophore A23187, dimethyl sulphoxide or indomethacin.
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Naor Z, Azrad A, Limor R, Zakut H, Lotan M. Gonadotropin-releasing hormone activates a rapid Ca2+-independent phosphodiester hydrolysis of polyphosphoinositides in pituitary gonadotrophs. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67116-9] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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293
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Guillon G, Mouillac B, Balestre MN. Activation of polyphosphoinositide phospholipase C by fluoride in WRK1 cell membranes. FEBS Lett 1986; 204:183-8. [PMID: 3015678 DOI: 10.1016/0014-5793(86)80808-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Partially purified plasma membranes prepared from myo-[3H]inositol-prelabeled WRK1 cells exhibit a phosphatidylinositol 4,5-biphosphate (PIP2) phospholipase C activity sensitive to NaF. NaF increased the production of IP2 and IP3 in a time- and concentration-dependent manner. The maximal increase in IP2 and IP3 production rates represented 400 +/- 18 and 360 +/- 40% of the basal production rate, respectively. Half-maximum stimulation was reached with 2-4 mM NaF. The observed effect was specific for F-. Aluminium potentiated fluoride-induced IP3 and IP2 accumulation in a concentration-dependent manner. The effect of fluoride on the PIP2 phospholipase C from WRK1 cell membranes appears to be similar to the well-documented effect of F- on the well-characterized Ns. Ni and transducin GTP-binding proteins. This observation constitutes an additional argument to suggest that a GTP-binding protein is involved in the process of receptor-mediated activation of PIP2 phospholipase C.
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294
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Carter HR, Bird IM, Smith AD. Two species of phospholipase C isolated from lymphocytes produce specific ratios of inositol phosphate products. FEBS Lett 1986; 204:23-7. [PMID: 3743760 DOI: 10.1016/0014-5793(86)81380-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Chromatography of the soluble porcine lymphocyte phospholipase C on cellulose phosphate resolves the activity into two species. An HPLC method is described for separating the enzyme products, Ins 1,2 greater than P and Ins 1P. Use of these methods reveals that the two iso-enzymes liberate, with a high degree of reproducibility, characteristic ratios of the two products. This suggests that the amount of each product produced is an inherent property of the enzyme mechanism.
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295
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Action of insulin on the subcellular metabolism of polyphosphoinositides in isolated rat hepatocytes. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67490-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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296
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Combettes L, Berthon B, Binet A, Claret M. Glucagon and vasopressin interactions on Ca2+ movements in isolated hepatocytes. Biochem J 1986; 237:675-83. [PMID: 3800909 PMCID: PMC1147044 DOI: 10.1042/bj2370675] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The effects of glucagon and vasopressin, singly or together, on cytosolic free Ca2+ concentration [( Ca2+]i) and on the 45Ca2+ efflux were studied in isolated rat liver cells. In the presence of 1 mM external Ca2+, glucagon and vasopressin added singly induced sustained increases in [Ca2+]i. The rate of the initial fast phase of the [Ca2+]i increase and the magnitude of the final plateau were dependent on the concentrations (50 pm-0.1 microM) of glucagon and vasopressin. Preincubating the cells with a low concentration of glucagon (0.1 nM) for 2 min markedly accelerated the fast phase and elevated the plateau of the [Ca2+]i increase caused by vasopressin. In the absence of external free Ca2+, glucagon and vasopressin transiently increased [Ca2+]i and stimulated the 45Ca2+ efflux from the cells, indicating mobilization of Ca2+ from internal store(s). Preincubating the cells with 0.1 nM-glucagon accelerated the rate of the fast phase of the [Ca2+]i rise caused by the subsequent addition of vasopressin. However, unlike what was observed in the presence of 1 mM-Ca2+, glucagon no longer enhanced the maximal [Ca2+]i response to vasopressin. In the absence of external free Ca2+, higher concentrations (1 nM-0.1 microM) of glucagon, which initiated larger increases in [Ca2+]i, drastically decreased the subsequent Ca2+ response to vasopressin (10 nM). At these concentrations, glucagon also decreased the vasopressin-stimulated 45Ca2+ efflux from the cells. It is suggested that, in the liver, glucagon accelerates the fast phase and elevates the plateau of the vasopressin-mediated [Ca2+]i increase respectively by releasing Ca2+ from the same internal store as that permeabilized by vasopressin, probably the endoplasmic reticulum, and potentiating the influx of extracellular Ca2+ caused by this hormone.
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297
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Studies on the hepatic calcium-mobilizing activity of aluminum fluoride and glucagon. Modulation by cAMP and phorbol myristate acetate. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67347-8] [Citation(s) in RCA: 133] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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298
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Giusto NM, Ilincheta de Boschero MG. Synthesis of polyphosphoinositides in vertebrate photoreceptor membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 877:440-6. [PMID: 3015222 DOI: 10.1016/0005-2760(86)90210-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Rod outer segments isolated from bovine retinas incorporated 32P into phospholipids after incubation with [gamma-32P]ATP in a Mg2+-containing medium. Only phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-bisphosphate, and phosphatidate were labelled. The incorporation of label into lipids was detected as early as 20 s after the start of incubation and the products were stable for at least 10 min. The reactions were time, protein and ATP-concentration dependent. Entire rod outer segments showed higher diacylglycerol kinase and lower phosphatidylinositol and phosphatidylinositol 4-phosphate kinase activities than the disc membranes obtained from them. Exogenously added phosphatidylinositol (up to 1 mM) in the presence of Triton X-100 increased phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate labelling in rod outer segments (8- and 6-fold, respectively). Triton X-100 at a concentration of 0.4% stimulated phosphorylation of endogenous phosphoinositides. Diacylglycerol kinase activity was largely suppressed by the detergent, but this effect was partially reversed by addition of phosphatidylinositol. It is suggested that the rod outer segments contain phosphatidylinositol kinase and phosphatidylinositol 4-phosphate kinase bound to disc membranes, as well as an active diacylglycerol kinase occurring either as a soluble or a peripherally bound protein in disc membranes.
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299
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Low MG, Carroll RC, Cox AC. Characterization of multiple forms of phosphoinositide-specific phospholipase C purified from human platelets. Biochem J 1986; 237:139-45. [PMID: 3026307 PMCID: PMC1146958 DOI: 10.1042/bj2370139] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The origin and physiological significance of the multiple Mr forms of phosphoinositide-specific phospholipase C in human platelets were investigated. The higher-Mr (400,000 and 270,000) forms of the phospholipase C were converted into the 100,000-Mr form without substantial loss of activity by incubation with a Ca2+-dependent proteinase partially purified from human platelets. These three forms of the phospholipase C were purified approx. 200-500-fold from outdated human platelet supernatants. SDS/polyacrylamide-gel electrophoresis and gel-filtration analysis suggested that the higher-Mr forms of phospholipase C were complexes of 140,000-Mr subunits, whereas the lower-Mr form consisted of a single 95,000-Mr subunit. The substrate specificity of the purified phospholipase C was investigated by using 32P-labelled polyphosphoinositide substrates purified from human platelets by a new method utilizing h.p.l.c. on an amino column. Activity against all three phosphoinositides was detected at micromolar concentrations of Ca2+; this hydrolysis was markedly stimulated by phosphatidylethanolamine and inhibited by phosphatidylcholine. Comparison of the different forms of purified phospholipase C revealed no major differences in Ca2+-sensitivity or substrate specificity. Thus, although the suggestion that the high-Mr forms of human platelet phosphoinositide-specific phospholipase C were converted into a lower-Mr form by a Ca2+-dependent proteinase has been substantiated, the physiological significance of this process remains to be determined.
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300
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