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Hossain MS, Afrose S, Sawada T, Hamano KI, Tsujii H. Metabolism of exogenous fatty acids, fatty acid-mediated cholesterol efflux, PKA and PKC pathways in boar sperm acrosome reaction. Reprod Med Biol 2009; 9:23-31. [PMID: 29699328 DOI: 10.1007/s12522-009-0036-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Accepted: 09/16/2009] [Indexed: 10/20/2022] Open
Abstract
Purpose For understanding the roles of fatty acids on the induction of acrosome reaction which occurs under association of cholesterol efflux and PKA or PKC pathways in boar spermatozoa, metabolic fate of alone and combined radiolabeled 14C-oleic acid and 3H-linoleic acid incorporated in the sperm was compared, and behavior of cholesterol and effects of PKA and PKC inhibitors upon fatty acid-induced acrosome reaction were examined. Methods Semen was collected from a Duroc boar, and the metabolic activities of fatty acids in the spermatozoa were measured using radioactive compounds and thin layer chromatography. Cholesterol efflux was measured with a cholesterol determination assay kit. Participation of fatty acids on the AR through PKA and PKC pathways was evaluated using a specific inhibitor of these enzymes. Results Incorporation rate of 14C-oleic acid into the sperm lipids was significantly higher than that of 3H-linoleic acid (P < 0.05). The oxidation of 14C-oleic acid was higher in combined radiolabeling rather than in one. The highest amounts of 3H-linoleic acid and 14C-oleic acid were recovered mainly in the triglycerides and phospholipids fraction, and 14C-oleic acid distribution was higher than the 3H-linoleic acid in both labeled (P < 0.05) sperm lipids. In the 3H-linoleic and 14C-oleic acid combined radiolabeling, the incorporation rate of the radioactive fatty acids in all the lipid fractions increased 15 times more than the alone radiolabeling. Boar sperm utilize oleic acid to generate energy for hyperactivation (P < 0.05). Supplementation of arachidonic acid significantly increased (P < 0.05) cholesterol efflux in sperm. When spermatozoa were incubated with PKA or PKC inhibitors, there was a significant reduction of arachidonic acid-induced acrosome reaction (AR) (P < 0.05), and inhibition by PKA inhibitor is stronger than that by PKC inhibitor. Conclusions Incorporation of unsaturated fatty acids, especially oleic acid, into triglycerides and phospholipids provides prerequisite energy for AR. Cholesterol efflux by arachidonic acid triggers AR. Arachidonic acid activated PKA and PKC pathway participate in induction of the AR.
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Affiliation(s)
- Md Sharoare Hossain
- Laboratory of Animal Biotechnology, Faculty of Agriculture Shinshu University Minamiminowa-mura 399-4598 Nagano Japan
| | - Sadia Afrose
- Laboratory of Animal Biotechnology, Faculty of Agriculture Shinshu University Minamiminowa-mura 399-4598 Nagano Japan
| | - Tomio Sawada
- The Sawada Women's Clinic Nagoya Reproduction Center Chikusaku Nagoya Aichi Japan
| | - Koh-Ichi Hamano
- Laboratory of Animal Biotechnology, Faculty of Agriculture Shinshu University Minamiminowa-mura 399-4598 Nagano Japan
| | - Hirotada Tsujii
- Laboratory of Animal Biotechnology, Faculty of Agriculture Shinshu University Minamiminowa-mura 399-4598 Nagano Japan
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Sugden MC, Holness MJ. Potential role of peroxisome proliferator-activated receptor-alpha in the modulation of glucose-stimulated insulin secretion. Diabetes 2004; 53 Suppl 1:S71-81. [PMID: 14749269 DOI: 10.2337/diabetes.53.2007.s71] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In this review, we discuss the influence of peroxisome proliferator-activated receptor (PPAR)-alpha on islet insulin secretion and develop the hypothesis that modulation of PPAR-alpha function may be important for the regulation of compensatory insulin secretion. We have attempted to analyze the role of PPAR-alpha-linked fatty acid metabolism in islet function in health and in insulin-resistant states linked to lifestyle factors, in particular pregnancy and a diet inappropriately high in saturated fat. We have emphasized the potential for both actions of PPAR-alpha on insulin sensitivity that may be relayed systemically to the islet, leading to modulation of the insulin response in accordance with changes in insulin sensitivity, and direct effects of PPAR-alpha action on the islet itself. Finally, we have developed the concept that compensatory insulin secretion may have a function not only in glucoregulation but also in liporegulation. Thus, augmented insulin secretion may reflect a requirement for lipid lowering as well as for increased glucose disposal and is perceived to aim to compensate for impaired suppression of islet lipid delivery by insulin. This introduces the possibility of a continuum between liporegulation with islet compensation and lipodysregulation leading to islet decompensation in the development of type 2 diabetes.
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Affiliation(s)
- Mary C Sugden
- Centre for Diabetes and Metabolic Medicine, Institute of Cell and Molecular Science, Barts and the London, Queen Mary's School of Medicine and Dentistry, University of London, London, UK.
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Roy K, Mandal AK, Sikdar R, Majumdar S, Ono Y, Sen PC. Unsaturated fatty acid-activated protein kinase (PKx) from goat testis cytosol. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1434:161-9. [PMID: 10556570 DOI: 10.1016/s0167-4838(99)00173-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The cytosolic fraction of goat cauda epididymis possesses a protein kinase (PKx) activity which is stimulated by a number of unsaturated fatty acids of which arachidonic acid is the best activator in absence of cAMP or Ca(2+). Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and diacylglycerol have no effect either alone or in combination. The membrane fraction does not show any appreciable kinase activity even after detergent treatment. PKx migrates as a single band of apparent molecular mass of 116 kDa on 10% SDS-PAGE after sequential chromatographic separation on DEAE-cellulose, phenyl-Sepharose, high-Q anion exchange and protamine-agarose affinity column. PKx phosphorylates histone H1, histone IIIs and protamine sulfate, but not casein. However, the best phosphorylation was obtained with a substrate based on PKC pseudosubstrate sequence (RFARKGSLRQKNV). The kinase phosphorylates two endogenous cytosolic proteins of 60 and 68 kDa. Ser residues are primarily phosphorylated although a low level of phosphorylation is observed on Thr residues also. Ca(2+) and Mn(2+) inhibit PKx activity in the micromolar range. Staurosporine is found to inhibit the PKx activity to a significant level at sub-nanomolar concentration. Lyso-phosphatidylcholine and certain detergents at very low concentrations (<0.05%) stimulate enzyme activity to some extent. The immuno-crossreactivity study with antibody against different PKC isotypes suggests that the protein kinase under study is not related to any known PKC family. Even the antibody against PKN (a related protein kinase reported in rat testis found to be activated by arachidonic acid) does not cross-react with this protein kinase. Hence we believe that the protein kinase (PKx) reported here is different even from the PKN of rat testis. The phosphorylation of endogenous proteins by the protein kinase may be involved in cell regulation including fertility regulation and signal transduction.
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Affiliation(s)
- K Roy
- Department of Chemistry, Bose Institute, 93/1 A.P.C. Road, Calcutta, India
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4
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El-Mansoury AM, Morgan NG. Activation of protein kinase C modulates alpha2-adrenergic signalling in rat pancreatic islets. Cell Signal 1998; 10:637-43. [PMID: 9794245 DOI: 10.1016/s0898-6568(98)00004-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Treatment of rat pancreatic islets with 4beta-phorbol-myristate-acetate (PMA) caused a significant reduction in the ability of the alpha2-adrenoceptor agonist noradrenaline to inhibit glucose-induced insulin secretion. This effect was most evident when low concentrations of the catecholamine were used (less than 1 microM) and was lost when the noradrenaline concentration was increased to 10 microM. The effect was probably mediated by activation of protein kinase C, because the ability of PMA to desensitise islets to noradrenaline was prevented by a selective inhibitor of calcium-dependent isoforms of the enzyme, Gö6976. The response to PMA was reproduced when islet protein kinase C was activated by a receptor-mediated mechanism involving incubation with the muscarinic agonist carbachol. In parallel with desensitisation of the inhibitory control of insulin secretion by noradrenaline, PMA treatment also reduced the ability of a low concentration of noradrenaline (0.1 microM) to inhibit islet cAMP formation. The loss of sensitivity to catecholamine, induced by PMA in rat islets, was not caused by any change in the levels of alpha2-adrenoceptor expression or in their ligand-binding affinity. It was, however, associated with a marked increase in the extent of phosphorylation of members of the Gi/Go, family of pertussis toxin-sensitive G proteins in PMA-treated islets. Immunoprecipitation of Gi alpha2 and Galpha o from 32P-labelled islets after treatment with PMA revealed that both G proteins are substrates for protein kinase C. Overall, the results indicate that activation of protein kinase C leads to phosphorylation of islet Gi and Go causing their uncoupling from alpha2-adrenoceptors. We propose that this mechanism may form an important component of a physiological system designed to limit the tendency for catecholamines to inhibit insulin secretion under conditions in which the parasympathetic innervation of the islets is activated.
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Affiliation(s)
- A M El-Mansoury
- Department of Biological Sciences, Keele University, Staffordshire, UK
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5
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Wilson JR, Ludowyke RI, Biden TJ. Nutrient stimulation results in a rapid Ca2+-dependent threonine phosphorylation of myosin heavy chain in rat pancreatic islets and RINm5F cells. J Biol Chem 1998; 273:22729-37. [PMID: 9712904 DOI: 10.1074/jbc.273.35.22729] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of protein kinases plays an important role in the Ca2+-dependent stimulation of insulin secretion by nutrients. The aim of the present study was to identify kinase substrates with the potential to regulate secretion because these have been poorly defined. Nutrient stimulation of the rat insulinoma RINm5F cell line and rat pancreatic islets resulted in an increase in the threonine phosphorylation of a 200-kDa protein. This was secondary to the gating of voltage-dependent Ca2+ channels because it was reproduced by depolarizing KCl concentrations and blocked by the Ca2+ channel antagonist, verapamil. The peak rises in [Ca2+]i preceded or were coincident with the maximal threonine phosphorylation in response to both glyceraldehyde and KCl. In digitonin-permeabilized RINm5F cells a rise in Ca2+ from 0.1 to 0.15 microM was sufficient to increase phosphorylation. Protein kinase C, protein kinase A, and Ca2+/calmodulin-dependent kinase II did not appear to be responsible for the phosphorylation, yet the Ca2+ dependence of the response suggests possible involvement of other members of the Ca2+/calmodulin-dependent kinase family. The 200-kDa protein was identified as myosin heavy chain by immunoprecipitation with a polyclonal nonmuscle myosin antibody. Phosphopeptide mapping indicated that the site of phosphorylation on myosin heavy chain was the same for both KCl- and glyceraldehyde-stimulated cells. Phosphoamino acid analysis confirmed a low basal phosphothreonine content of myosin heavy chain, which increased 6-fold in response to KCl. A lesser (2-fold) increase in serine phosphorylation was also detected using this technique. Although myosin IIA and IIB were shown to be present in RINm5F cells and rat islets, myosin IIA was the predominant threonine-phosphorylated species, suggesting that the two myosin species might be independently regulated. Our results identify myosin heavy chain as a novel kinase substrate in pancreatic beta-cells and suggest that it might play an important role in the regulation of insulin secretion.
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Affiliation(s)
- J R Wilson
- Garvan Institute of Medical Research, St. Vincent's Hospital, University of New South Wales, Sydney, New South Wales 2010, Australia
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6
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Jones PM, Persaud SJ. Protein kinases, protein phosphorylation, and the regulation of insulin secretion from pancreatic beta-cells. Endocr Rev 1998; 19:429-61. [PMID: 9715374 DOI: 10.1210/edrv.19.4.0339] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College London, United Kingdom.
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7
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Ashcroft SJ. Intracellular second messengers. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 426:73-80. [PMID: 9544257 DOI: 10.1007/978-1-4899-1819-2_9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- S J Ashcroft
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, United Kingdom
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8
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Jones PM, Persaud SJ. Ca(2+)-induced loss of Ca2+/calmodulin-dependent protein kinase II activity in pancreatic beta-cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:E708-15. [PMID: 9575833 DOI: 10.1152/ajpendo.1998.274.4.e708] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Elevations in intracellular Ca2+ in electrically permeabilized islets of Langerhans produced rapid insulin secretory responses from beta-cells, but the Ca(2+)-induced secretion was not maintained and was irrespective of the pattern of administration of elevated Ca2+. Ca(2+)-insensitive beta-cells responded normally to activators of protein kinase C or cAMP-dependent kinase with increased insulin secretion. The loss of secretory responsiveness to Ca2+ was paralleled by a reduction in Ca(2+)-induced protein phosphorylation. This was caused by a reduction in Ca2+/calmodulin-dependent protein kinase II (CaMK II) activity in the desensitized cells, as assessed by measuring the phosphorylation of a CaMK II-specific exogenous substrate, autocamtide-2. The Ca(2+)-induced reductions in kinase activity and protein phosphorylation were not dependent on the activation of Ca(2+)-dependent protein kinases and were not caused by the activation of phosphoprotein phosphatases or of Ca(2+)-activated proteases. The concomitant reductions in CaMK II activity and Ca(2+)-induced insulin secretion suggest that the activation of CaMK II is required for normal insulin secretory responses to increased intracellular Ca2+ concentrations.
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Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College London, United Kingdom
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9
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Harris TE, Persaud SJ, Jones PM. Pseudosubstrate inhibition of cyclic AMP-dependent protein kinase in intact pancreatic islets: effects on cyclic AMP-dependent and glucose-dependent insulin secretion. Biochem Biophys Res Commun 1997; 232:648-51. [PMID: 9126329 DOI: 10.1006/bbrc.1997.6344] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Synthetic peptides derived from the endogenous protein kinase A inhibitor (PKI) offer a specific means of inhibiting cyclic AMP-dependent protein kinase A (PKA), but their use in whole cells is restricted by the plasma membrane. We have now modified PKI sequences by N-terminal myristoylation to enhance their membrane permeability, and have used the myristoylated (myr) peptides to investigate the role of PKA activation in glucose-induced insulin secretion from intact pancreatic beta-cells. The myristoylated PKI peptides, myr PKI14-22 and myrPKI6-22, were effective inhibitors in vitro of PKA activity extracted from rat islets of Langerhans. In experiments using intact islets, myr PKI14-22 caused a concentration-dependent inhibition of insulin secretion in response to the PKA activators dibutyryl cyclic AMP and forskolin, suggesting that it gained access to the cytosolic compartment of intact beta-cells and inhibited PKA in situ. However, these concentrations of myr PKI14-22 did not inhibit insulin secretion in response to glucose suggesting that the activation of PKA is not required for the initiation of glucose-induced insulin secretion.
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Affiliation(s)
- T E Harris
- Biomedical Sciences Division, King's College London, United Kingdom
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10
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Dunlop M, Clark S. Glucose-induced phosphorylation and activation of a high molecular weight cytosolic phospholipase A2 in neonatal rat pancreatic islets. Int J Biochem Cell Biol 1995; 27:1191-9. [PMID: 7584605 DOI: 10.1016/1357-2725(95)00093-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Previous studies have shown that stimulus-secretion coupling for the release of insulin from the pancreatic islet is potentiated by phospholipase A2 activity. Several biochemically distinct phospholipase A2 activities have been described in the islet. A recently identified cytosolic high molecular weight phospholipase A2, which requires Ca2+ for association with cellular membranes but not for catalytic activity can be activated in a protein kinase C-dependent manner in other cell-types. We determined its phosphorylation and activation in response to phorbol ester and glucose in cultured islet cells from neonatal rats. Islet cell monolayers were labelled to equilibrium with [32P]orthophosphate. Following stimulation cytosolic phospholipase A2 was immunoprecipitated and, after electrophoretic separation and transfer to nitrocellulose membrane, 32P-labelled protein was detected by autoradiography. Phospholipase A2 activity of islet cell cytosol was determined by hydrolysis of exogenous I-stearyl- 2[14C]arachidonyl phosphatidylcholine substrate. It could be shown that phosphorylation of immunoprecipitated phospholipase A2 was augmented by prolonged glucose exposure (> 1 hr) in a protein kinase C-dependent manner. Phosphorylation occurred concomitant with a glucose-induced increase in total cellular phospholipase A2 activity (177 +/- 3 nmol substrate hydrolysed/mg protein at glucose 5.6 mM vs 267 +/- 32 (SEM, n = 4) at glucose 25 mM, P < 0.05). Both acute protein kinase C (459 +/- 71) and glucose-activated phospholipase A2 activities were reduced in the presence of a specific arachidonic acid analogue inhibitor of cytosolic phospholipase A2 (to 231 +/- 10 and 161 +/- 17, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Dunlop
- University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville, Victoria, Australia
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11
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Kitagawa M, Mukai H, Shibata H, Ono Y. Purification and characterization of a fatty acid-activated protein kinase (PKN) from rat testis. Biochem J 1995; 310 ( Pt 2):657-64. [PMID: 7654208 PMCID: PMC1135946 DOI: 10.1042/bj3100657] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
PKN, a novel protein kinase with a catalytic domain homologous to that of the protein kinase C (PKC) family and unique N-terminal leucine-zipper-like sequences, was identified by molecular cloning from a human hippocampus cDNA library [Mukai and Ono (1994) Biochem. Biophys. Res. Commun. 199, 897-904]. Recently we partially purified recombinant PKN from COS7 cells transfected with the cDNA construct encoding human PKN, and demonstrated that the recombinant PKN was activated by unsaturated fatty acids and limited proteolysis [Mukai, Kitagawa, Shibata et al. (1994) Biochem. Biophys. Res. Commun. 204, 348-356]. The present work has focused on the further purification and characterization of PKN from native rat tissue. Immunochemical measurement revealed that PKN was found in every tissue, and was especially abundant in testis, spleen and brain; subcellular fractionation of rat brain showed that half of the PKN was localized in the soluble cytosolic fraction. PKN was purified approx. 8000-fold to apparent homogeneity from the cytosolic fraction of rat testis by DEAE-cellulose chromatography, ammonium sulphate fractionation and chromatography on butyl-Sepharose, heparin-Sepharose, Mono Q and protamine-CH-Sepharose. The enzyme migrates as a band of apparent molecular mass 120 kDa. Using serine-containing peptides based on the pseudosubstrate sequence of PKC-delta as phosphate acceptors, the kinase activity was stimulated several-fold by 40 microM unsaturated fatty acids or by detergents such as 0.04% sodium deoxycholate and 0.004% SDS. In the absence of modifiers, protamine sulphate, myelin basic protein and synthetic peptides based on the pseudosubstrate site of PKCs or ribosomal S6 protein were good substrates for phosphorylation by the kinase. In the presence of 40 microM arachidonic acid the kinase activity of PKN for these phosphate acceptors was increased 2-18-fold. The autophosphorylation activity of purified PKN was partially inhibited by pretreatment with alkaline phosphatase. These properties appear to distinguish PKN from many protein kinases isolated previously.
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Affiliation(s)
- M Kitagawa
- Department of Biology, Faculty of Science, Kobe University, Japan
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Basudev H, Jones PM, Howell SL. Protein phosphorylation in the regulation of insulin secretion: the use of site-directed inhibitory peptides in electrically permeabilised islets of Langerhans. Acta Diabetol 1995; 32:32-7. [PMID: 7612915 DOI: 10.1007/bf00581042] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have used electrically permeabilised rat islets of Langerhans to investigate the role of protein phosphorylation in the regulation of insulin secretion using pseudosubstrate inhibitory peptides for cyclic AMP-dependent protein kinase (PKA) and for protein kinase C (PKC). The protein kinase inhibitor (PKI) peptide, PKI(6-22), completely inhibited the effects of cyclic AMP on islet PKA activity in vitro, on endogenous protein phosphorylation and on insulin secretion. This peptide had no significant effect on islet PKC activity in vitro, on Ca(2+)-induced protein phosphorylation and on secretory responses to Ca2+ or to the PKC activator, 4 beta-phorbol myristate acetate (PMA). The PKC pseudosubstrate inhibitory peptide, PKC(19-36), caused a marked inhibition of islet PKC activity in vitro and inhibite PMA-induced insulin secretion without affecting secretory responses to cyclic AMP and Ca2+. These results demonstrate that PKA- and PKC-induced protein phosphorylation is obligatory for cyclic AMP- and PMA-stimulated insulin secretion, respectively, and suggest that there is little "crosstalk" between the response elements of the secretory pathways to the different second messengers, at least after the generation of the messengers within the beta-cells.
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Affiliation(s)
- H Basudev
- Biomedical Sciences Division, King's College London, Kensington, UK
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13
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Abstract
The central role of reversible protein phosphorylation in regulation of beta-cell function is reviewed and the properties of the protein kinases so far defined in beta cells are summarised. The key effect of Ca2+ to initiate insulin secretion involves activation of a Ca2+/calmodulin-dependent protein kinase. Potentiation of secretion by agents activating protein kinase A or C appears to involve an increase in the sensitivity of the secretory system to intracellular Ca2+. The effects of MgATP on the binding of [3H]-glibenclamide to the beta-cell sulphonylurea receptor suggest that the properties of this receptor, which controls the activity of ATP-sensitive K-channels, are modulated by phosphorylation. The identity of the kinases and phosphatases responsible is not known but the presence in beta-cell membranes of various kinases not dependent on Ca2+ or cyclic AMP, and including tyrosine kinase, is documented, together with the presence of both Ca(2+)-dependent and Ca(2+)-independent protein phosphatases. Protein phosphorylation is also involved in regulation of beta-cell Ca2+ fluxes and evidence is presented that protein kinase C activation inhibits Ca2+ signalling by reducing influx of Ca2+ into the beta cell. The identity of the Ca2+/calmodulin-dependent protein kinase activity in beta cells is discussed. Comparison of its properties towards substrates and inhibitors with those of brain Ca2+/calmodulin-dependent protein kinase II suggests that the beta-cell enzyme may be similar or identical to the brain enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S J Ashcroft
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Oxford, UK
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Ashcroft FM, Proks P, Smith PA, Ammälä C, Bokvist K, Rorsman P. Stimulus-secretion coupling in pancreatic beta cells. J Cell Biochem 1994; 55 Suppl:54-65. [PMID: 7929618 DOI: 10.1002/jcb.240550007] [Citation(s) in RCA: 208] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Insulin secretion is triggered by a rise in the intracellular Ca2+ concentration that results from the activation of voltage-gated Ca2+ channels in the beta-cell plasma membrane. Multiple types of beta-cell Ca2+ channel have been identified in both electrophysiological and molecular biological studies, but it appears that the L-type Ca2+ channel plays a dominant role in regulating Ca2+ influx. Activity of this channel is potentiated by protein kinases A and C and is inhibited by GTP-binding proteins, which may mediate the effects of potentiators and inhibitors of insulin secretion on Ca2+ influx, respectively. The mechanisms by which elevation of intracellular Ca2+ leads to the release of insulin granules is not fully understood but appears to involve activation of Ca2+/calmodulin-dependent protein kinase. Phosphorylation by either protein kinase A or C, probably at different substrates, potentiates insulin secretion by acting at some late stage in the secretory process. There is also evidence that small GTP-binding proteins are involved in regulating exocytosis in beta cells. The identification and characterisation of the proteins involved in exocytosis in beta cells and clarification of the mechanism(s) of action of Ca2+ is clearly an important goal for the future.
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Affiliation(s)
- F M Ashcroft
- University Laboratory of Physiology, Oxford, England
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Diaz GB, Paladini AA, Garcia ME, Gagliardino JJ. Changes induced by hypothyroidism in insulin secretion and in the properties of islet plasma membranes. ARCHIVES INTERNATIONALES DE PHYSIOLOGIE, DE BIOCHIMIE ET DE BIOPHYSIQUE 1993; 101:263-9. [PMID: 7508283 DOI: 10.3109/13813459309003922] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
This work was aimed at elucidating the effect of thyroid function on the physiology and biochemistry of the islet-cell population within the endocrine pancreas. To this end, we performed a comparative study of the physiochemical properties of islet-cell membranes and of the dynamics of glucose-induced insulin secretion in isolated pancreatic islets prepared from euthyroid i.e. control (C), hypothyroid (H), and thyroxin-supplemented hypothyroid (HT) rats. H rats were obtained by injecting normal rats with 131iodine, while HT rats consisted of H rats treated with thyroxin (T4). Insulin secretion was studied in isolated islets perifused with 3.3 and 16.6 mM glucose. Physicochemical properties of the partially purified islet plasma membranes were assessed by measurements of fluorescence polarization with the fluorophore 1,6-diphenyl-1,3,5-hexatriene (DPH) as a lipidic molecular probe. Insulin output during either the first or second phase of insulin secretion in H islets was significantly lower than in C islets. The slope of the curve in the second phase of insulin secretion was also lesser in H than in C islets, suggesting an additional defect in their velocity of hormone release. T4 administration of H rats reversed the decrease in insulin output to the range found in C islets but was incapable of correcting the defect in the hormone-secretion velocity. Several changes were found in the physicochemical properties of the membranes obtained from H islets as compared to C islets.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- G B Diaz
- CENEXA-Centro de Endocrinologia Experimental y Aplicada (UNLP-CONICET), Facultad de Ciencias Médicas, La Plata, Argentina
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Persaud SJ, Jones PM, Howell SL. Staurosporine inhibits protein kinases activated by Ca2+ and cyclic AMP in addition to inhibiting protein kinase C in rat islets of Langerhans. Mol Cell Endocrinol 1993; 94:55-60. [PMID: 8397122 DOI: 10.1016/0303-7207(93)90051-k] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Staurosporine has been used in several studies to investigate the role of protein kinase C (PKC) in secretory responses of islets of Langerhans to insulin secretagogues. We have assessed the effect of staurosporine on: [i] islet PKC activity in vitro; [ii] the stimulation of insulin secretion by nutrient secretagogues and [iii] the stimulation of protein phosphorylation and insulin secretion in electrically permeabilised islets. All experiments were carried out on rat isolated islets of Langerhans, either intact or permeabilised by high voltage discharge (3.4 kV/cm). The activity of PKC partially purified from rat islets was inhibited by staurosporine (1.6-400 nM) in a concentration-dependent manner. Staurosporine also inhibited insulin secretion stimulated by both glucose and glyceraldehyde, with maximal effects at 50 nM. After prolonged exposure of islets to the tumour-promoting phorbol ester, 4 beta phorbol myristate acetate (4 beta PMA), a procedure which depletes islet PKC activity, staurosporine still inhibited both glucose- and glyceraldehyde-stimulated insulin release. In electrically permeabilised islets, staurosporine inhibited both Ca(2+)- and cyclic AMP-stimulated protein phosphorylation and insulin secretion. These results suggest that staurosporine should not be used as a selective inhibitor of PKC in rat islets.
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Affiliation(s)
- S J Persaud
- Biomedical Sciences Division, King's College London, UK
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Jones PM, Mann FM, Persaud SJ, Wheeler-Jones CP. Mastoparan stimulates insulin secretion from pancreatic beta-cells by effects at a late stage in the secretory pathway. Mol Cell Endocrinol 1993; 94:97-103. [PMID: 8397124 DOI: 10.1016/0303-7207(93)90056-p] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Mastoparan (MP) is a component of wasp venom which stimulates secretion from a number of cell types. We have used intact and electrically permeabilised islets of Langerhans to investigate the mechanisms through which MP stimulates insulin secretion from pancreatic beta-cells. MP caused a temperature-dependent and dose-related stimulation of insulin secretion from intact islets at a substimulatory concentration (2 mM) of glucose, which was not dependent upon the presence of extracellular Ca2+. MP also stimulated ATP-independent insulin secretion from electrically permeabilised islets in which intracellular Ca2+ was clamped at a substimulatory concentration (50 nM). MP-induced insulin secretion was not inhibited by down-regulation of islet protein kinase C, nor by the protein kinase inhibitor staurosporine, nor by the cyclic AMP antagonist Rp-adenosine 3',5'-cyclic phosphorothioate. However, MP-induced secretion from permeabilised islets was inhibited by the presence of guanosine 5'-O-2-thiodiphosphate. These results suggest that MP stimulates insulin secretion by a mechanism that is independent of changes in cytosolic Ca2+ or protein kinase activation, but which is dependent, at least in part, upon activation of a GTP-binding protein at a late stage in the secretory process.
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Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College London, Kensington, UK
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18
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Ebner K, Matsumura F, Enan E, Olsen H. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters pancreatic membrane tyrosine phosphorylation following acute treatment. JOURNAL OF BIOCHEMICAL TOXICOLOGY 1993; 8:71-81. [PMID: 8355262 DOI: 10.1002/jbt.2570080204] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
To understand the basic mechanisms of TCDD's action to cause hypoinsulinemia in several experimental animals, we have studied TCDD-induced changes in various protein kinase activities in membrane preparations of guinea pig pancreas. For this purpose, young male guinea pigs were treated through a single intraperitoneal injection with 1 or 3 micrograms/kg of TCDD in vivo, and, after given time periods, pancreas samples were obtained and membranes were isolated through homogenization and centrifugation procedures. Several sets of incubation conditions were selected for protein kinase activity assay, each favoring a specific type of protein kinase. It was found that overall protein phosphorylation activities were higher in the preparation from TCDD-treated animals as compared to those found in pair-fed controls and that this trend was more pronounced when the assay medium contained Mn2+ in place of Mg2+ and EGTA. These are the conditions that are known to favor protein tyrosine kinases. Other types of protein kinases from the treated animals did not show any significant differences from the pair-fed control animals, though that of protein kinase C in the treated preparation showed a modest increase. To establish that the type of protein kinases stimulated by TCDD are protein tyrosine kinases, we have carried out phosphoamino acid analyses, KOH digestion, and western blot analyses using an antibody to phosphotyrosine. All the results were consistent in supporting the idea that TCDD causes a rise in protein-tyrosine kinases in pancreas at early stages of poisoning.
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Affiliation(s)
- K Ebner
- Pesticide Research Center, Michigan State University, East Lansing 48824
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19
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Hughes SJ, Smith H, Ashcroft SJ. Characterization of Ca2+/calmodulin-dependent protein kinase in rat pancreatic islets. Biochem J 1993; 289 ( Pt 3):795-800. [PMID: 8382051 PMCID: PMC1132246 DOI: 10.1042/bj2890795] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have attempted to identify islet Ca2+/calmodulin-dependent protein kinase (CaM kinase) by comparing its activity with purified brain CaM kinase II. Islet CaM kinase, in the presence of calmodulin and Ca2+, phosphorylated major endogenous substrates of 102, 57 and 53 kDa and also exogenous glycogen synthase; brain CaM kinase II phosphorylated glycogen synthase and peptides of 57 and 53 kDa. Alloxan (1 mM) inhibited the phosphorylation of glycogen synthase and the 102, 57 and 53 kDa islet peptides by islet CaM kinase; the phosphorylation of glycogen synthase and the 57 and 53 kDa substrates by brain CaM kinase II was also inhibited by alloxan. The Ca2+ and calmodulin-dependencies of phosphorylation of the endogenous islet substrates differed. In the presence of 400 nM calmodulin, half-maximal phosphorylation was attained at Ca2+ concentrations of 80 +/- 9, 401 +/- 61 and 459 +/- 59 nM for the 102, 57 and 53 kDa substrates respectively. In the presence of 10 microM Ca2+, half-maximal phosphorylation was attained at calmodulin concentrations of 9 +/- 2, 38 +/- 2.5 and 37 +/- 2 nM for the 102, 57 and 53 kDa substrates respectively. Differential centrifugation located the 102 kDa substrate in the post-100,000 g supernatant and the 57 and 53 kDa substrates in the particulate fraction. These data suggest that islet CaM kinase is similar to, if not identical with, brain CaM kinase II, but that phosphorylation of the endogenous 102 kDa substrate occurs by a distinct kinase which shows different sensitivities to Ca2+ and calmodulin. This kinase probably corresponds to CaM kinase III and the 102 kDa peptide to elongation factor 2 (EF-2), since the 102 kDa peptide was shown to undergo ADP-ribosylation in the presence of diphtheria toxin and NAD+.
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Affiliation(s)
- S J Hughes
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, U.K
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20
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Basudev H, Jones PM, Persaud SJ, Howell SL. Arachidonic acid-induced insulin secretion from rat islets of Langerhans is not mediated by protein phosphorylation. Mol Cell Endocrinol 1993; 91:193-9. [PMID: 8386112 DOI: 10.1016/0303-7207(93)90272-l] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Arachidonic acid (AA) stimulated protein phosphorylation in electrically permeabilised islets, most notably of an islet protein of approximate molecular weight 18 kDa. This protein did not appear to be a substrate for cAMP-dependent protein kinase. The AA-induced protein phosphorylation was mediated by unmetabolised AA since the lipoxygenase inhibitor, nordihydroguaretic acid (NDGA), or the cyclooxygenase inhibitor, indomethacin, did not significantly reduce AA-induced phosphorylation. Although saturated fatty acids did not stimulate phosphorylation of islet proteins, a number of cis-unsaturated fatty acids, other than AA, induced 32P incorporation into an 18 kDa protein. However, some fatty acids which stimulated protein phosphorylation had no effect on insulin secretion in experiments where AA clearly stimulated insulin secretion. AA stimulated protein kinase C (PKC) activity extracted from islets but several fatty acids which induced protein phosphorylation had no significant effect on PKC activity in vitro. 50 nM staurosporine had no effect on AA-induced protein phosphorylation but this concentration of staurosporine markedly inhibited PKC activity. 200 nM staurosporine caused complete inhibition of the AA-induced phosphorylation without having any effect on AA-induced insulin secretion. These results suggest that AA and some other fatty acids can promote 32P incorporation into islet proteins, independently of PKC activation, and that AA-induced phosphorylation is not required for insulin secretory responses to AA.
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Affiliation(s)
- H Basudev
- Biomedical Sciences Division, King's College London, UK
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21
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Ratcliff H, Jones PM. Effects of okadaic acid on insulin secretion from rat islets of Langerhans. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1175:188-91. [PMID: 8380341 DOI: 10.1016/0167-4889(93)90022-h] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have studied the effects of the phosphatase inhibitor, okadaic acid, on insulin secretion and protein phosphorylation in intact and electrically permeabilized pancreatic islets. Okadaic acid inhibited glucose-induced insulin secretion from intact islets, although this effect was probably non-specific since similar effects were obtained using 1-nor-okadaone, a virtually inactive analogue of okadaic acid. In permeabilized islets, okadaic acid enhanced basal and cyclic-AMP-induced insulin secretion and protein phosphorylation. These results indicate that protein phosphatases may play a role in the regulation of insulin release.
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Affiliation(s)
- H Ratcliff
- Biomedical Sciences Division, King's College London, UK
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22
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Persaud SJ, Jones PM, Howell SL. Activation of protein kinase C partially alleviates noradrenaline inhibition of insulin secretion. Biochem J 1993; 289 ( Pt 2):497-501. [PMID: 7678735 PMCID: PMC1132195 DOI: 10.1042/bj2890497] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The sympathetic neurotransmitter noradrenaline (NA) fully inhibited both phases of glucose-stimulated insulin secretion from rat islets of Langerhans. The secretory response to the protein kinase C (PKC) activator, 4 beta-phorbol myristate acetate (4 beta PMA), in the absence of exogenous glucose was also abolished by NA. However, at 20 mM glucose 4 beta PMA partially alleviated the inhibitory effect of NA both on insulin release and on cyclic AMP generation. Inhibition of insulin release by NA, albeit much decreased, was still observed in the presence of maximal stimulatory concentrations of both 4 beta PMA and dibutyryl cyclic AMP. The relieving effect of 4 beta PMA on the inhibition of insulin secretion by NA was not overcome by the competitive antagonist of cyclic AMP-dependent protein kinase, Rp-adenosine 3',5'-cyclic phosphorothioate. Down-regulation of islet PKC activity by overnight exposure to 4 beta PMA did not affect the inhibitory capacity of NA. These results suggest that NA inhibits insulin release independently of interaction with PKC, but that activation of this enzyme decreases the inhibitory effect of NA at stimulatory concentrations of glucose. This protective effect of 4 beta PMA could not be attributed to a decrease in NA inhibition of cyclic AMP generation.
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Affiliation(s)
- S J Persaud
- Biomedical Sciences Division, King's College London, U.K
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23
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Wenham RM, Landt M, Walters SM, Hidaka H, Easom RA. Inhibition of insulin secretion by KN-62, a specific inhibitor of the multifunctional Ca2+/calmodulin-dependent protein kinase II. Biochem Biophys Res Commun 1992; 189:128-33. [PMID: 1333187 DOI: 10.1016/0006-291x(92)91534-w] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The effects of KN-62, a specific inhibitor of Ca2+/calmodulin-dependent protein kinase II (CamPKII), on insulin secretion and protein phosphorylation were studied in rat pancreatic islets and RINm5F cells. KN-62 was found to dose-dependently inhibit autophosphorylation of CamPKII in subcellular preparations of RINm5F cells (K0.5 = 3.1 +/- 0.3 microM), but had no effect on protein kinase C or myosin light chain kinase activity. KN-62, but not the inactive analogue KN-04, dose-dependently inhibited glucose-induced insulin release (K0.5 = 1.5 +/- 0.5 microM) in a manner similar to the inhibition of CamPKII autophosphorylation. KN-62 (10 microM) inhibited carbachol (in the presence of 8 mM glucose) and potassium-stimulated insulin secretion from islets by 53% and 59%, respectively. These results support a role of CamPKII in glucose-sensitive insulin secretion.
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Affiliation(s)
- R M Wenham
- Department of Biochemistry and Molecular Biology, Texas College of Osteopathic Medicine, Fort Worth 76107
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24
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Jones PM, Persaud SJ, Howell SL. Ca2(+)-induced insulin secretion from electrically permeabilized islets. Loss of the Ca2(+)-induced secretory response is accompanied by loss of Ca2(+)-induced protein phosphorylation. Biochem J 1992; 285 ( Pt 3):973-8. [PMID: 1323277 PMCID: PMC1132890 DOI: 10.1042/bj2850973] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Increasing the cytosolic Ca2+ concentration of electrically permeabilized rat islets of Langerhans caused rapid increases in insulin secretion and in 32P incorporation into islet proteins. However, the secretory responsiveness of permeabilized islets was relatively transient, with insulin secretion approaching basal levels within 20-30 min despite the continued presence of stimulatory concentrations of Ca2+. The loss of Ca2(+)-induced insulin secretion was accompanied by a marked reduction in Ca2(+)-dependent protein phosphorylation, but not in cyclic AMP-dependent protein phosphorylation. Similarly, permeabilized islets which were no longer responsive to Ca2+ were able to mount appropriate secretory responses to cyclic AMP and to a protein kinase C-activating phorbol ester. These results suggest that prolonged exposure to elevated cytosolic Ca2+ concentrations results in a specific desensitization of the secretory mechanism to Ca2+, perhaps as a result of a decrease in Ca2(+)-dependent kinase activity. Furthermore, these studies suggest that secretory responses of B-cells to cyclic AMP and activators of protein kinase C are not dependent upon the responsiveness of the cells to changes in cytosolic Ca2+.
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Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College London, England
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25
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Landt M, Easom RA, Colca JR, Wolf BA, Turk J, Mills LA, McDaniel ML. Parallel effects of arachidonic acid on insulin secretion, calmodulin-dependent protein kinase activity and protein kinase C activity in pancreatic islets. Cell Calcium 1992; 13:163-72. [PMID: 1315620 DOI: 10.1016/0143-4160(92)90044-s] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A potential role of arachidonic acid in the modulation of insulin secretion was investigated by measuring its effects on calmodulin-dependent protein kinase and protein kinase C in islet subcellular fractions. The results were interpreted in the light of arachidonic acid effects on insulin secretion from intact islets. Arachidonic acid could replace phosphatidylserine in activation of cytosolic protein kinase C (K0.5 of 10 microM) and maximum activation was observed at 50 microM arachidonate. Arachidonic acid did not affect the Ca2+ requirement of the phosphatidylserine-stimulated activity. Arachidonic acid (200 microM) inhibited (greater than 90%) calmodulin-dependent protein kinase activity (K0.5 = 50-100 microM) but modestly increased basal phosphorylation activity (no added calcium or calmodulin). Arachidonic acid inhibited glucose-sensitive insulin secretion from islets (K0.5 = 24 microM) measured in static secretion assays. Maximum inhibition (approximately 70%) was achieved at 50-100 microM arachidonic acid. Basal insulin secretion (3 mM glucose) was modestly stimulated by 100 microM arachidonic acid but in a non-saturable manner. In perifusion secretion studies, arachidonic acid (20 microM) had no effect on the first phase of glucose-induced secretion but nearly completely suppressed second phase secretion. At basal glucose (4 mM), arachidonic acid induced a modest but reproducible biphasic insulin secretion response which mimicked glucose-sensitive secretion. However, phosphorylation of an 80 kD protein substrate of protein kinase C was not increased when intact islets were incubated with arachidonic acid, suggesting that the small increases in insulin secretion seen with arachidonic acid were not mediated by protein kinase C. These data suggest that arachidonic acid generated by exposure of islets to glucose may influence insulin secretion by inhibiting the activity of calmodulin-dependent protein kinase but probably has little effect on protein kinase C activity.
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Affiliation(s)
- M Landt
- Department of Paediatrics, Washington University School of Medicine, St Louis, Missouri
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26
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Basudev H, Jones PM, Persaud SJ, Howell SL. Arachidonic acid induces phosphorylation of an 18 kDa protein in electrically permeabilised rat islets of Langerhans. FEBS Lett 1992; 296:69-72. [PMID: 1730293 DOI: 10.1016/0014-5793(92)80405-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Arachidonic acid (AA) was shown to induce concentration-dependent, calcium-independent, in situ phosphorylation of a protein of approximate molecular weight 18 kDa in electrically permeabilised rat islets of Langerhans. This protein did not appear to be a substrate for protein kinase C (PKC) since stimulation of PKC by 4 beta phorbol myristate acetate (4 beta PMA) did not result in 32P incorporation into an 18 kDa protein, and since AA-induced phosphorylation was observed in islets in which PKC had been down-regulated by prolonged exposure of islets to 4 beta PMA. These results suggest that AA stimulates protein phosphorylation by a mechanism other than PKC activation.
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Affiliation(s)
- H Basudev
- Biomedical Sciences Division, King's College London, Kensington, UK
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27
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Jones PM, Persaud SJ, Howell SL. Insulin secretion and protein phosphorylation in PKC-depleted islets of Langerhans. Life Sci 1992; 50:761-7. [PMID: 1740960 DOI: 10.1016/0024-3205(92)90180-w] [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: 12/28/2022]
Abstract
Protein kinase C (PKC)-dependent phosphorylation of endogenous substrates was measured in electrically permeabilised rat islets of Langerhans. The PKC-activating phorbol ester, 4 beta-phorbol myristate acetate (PMA), caused a slow but prolonged increase in insulin secretion from permeabilised islets, which was accompanied by increased 32P incorporation into several islet proteins of apparent M.W. 30-50 kDa. Depletion of islet PKC by prolonged exposure to PMA abolished subsequent secretory and phosphorylating responses to the phorbol ester. However, PKC-depleted islets did not show diminished responses to glucose, suggesting that PKC-mediated phosphorylation of these proteins is not essential for nutrient-induced insulin secretion.
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Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College, London, U.K
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28
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Zawalich WS, Zawalich KC, Ganesan S, Calle R, Rasmussen H. Effects of the phorbol ester phorbol 12-myristate 13-acetate (PMA) on islet-cell responsiveness. Biochem J 1991; 278 ( Pt 1):49-56. [PMID: 1652943 PMCID: PMC1151447 DOI: 10.1042/bj2780049] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Collagenase-isolated rat islets were labelled for 2 h in myo-[2-3H]inositol solution supplemented with 2.75 mM-glucose. The phorbol ester phorbol 12-myristate 13-acetate (PMA; 0.1 or 1 microM) was also present in some experiments. After labelling, islets were washed and then perifused in 2.75 mM-glucose to establish basal [3H]inositol-efflux and insulin-secretory rates. Subsequently, the responses of these islets to stimulation with various agonists were assessed. Inositol phosphate accumulation was measured at the termination of the perifusion. In separate experiments, the cellular location of protein kinase C (PKC) after PMA pretreatment was measured by quantitative immunoblotting of membrane and cytosolic fractions. The following observations were made. (1) Labelling in 0.1-1 microM-PMA had no deleterious effect on total [3H]inositol incorporation during the 2 h labelling period. However, islets labelled for 2 h in 1 microM-PMA were unable to respond, in terms of increases in insulin release, to a 1 microM-PMA stimulus during the subsequent perifusion. (2) As compared with the responses of control islets labelled in 2.75 mM-glucose alone, islets labelled in the additional presence of 1 microM-PMA displayed a significant impairment in phosphoinositide (PI) hydrolysis, but an enhancement of both first-and second-phase insulin secretion, in response to subsequent 20 mM-glucose stimulation. (3) Decreasing extracellular Ca2+ level to 0.1 mM and including the Ca(2+)-channel antagonist nitrendipine (0.5 microM) along with 1 microM-PMA during the [3H]inositol-labelling period did not alter the response of the islets to the subsequent addition of 20 mM-glucose. Glucose-induced PI hydrolysis was still inhibited and 20 mM-glucose-induced insulin release was still enhanced. (4) A markedly amplified and sustained insulin-secretory response to 200 microM-tolbutamide in the presence of 2.75 mM-glucose was also obtained from 1 microM-PMA-pretreated islets. This contrasts sharply with the small and transient response to tolbutamide noted in control islets. (5) When present only during the perifusion phase of the experiments, nitrendipine (0.5 microM) abolished the amplified insulin-secretory responses to both 20 mM-glucose and 200 microM-tolbutamide noted in PMA-pretreated islets. (6) Prior labelling in 1 microM-PMA dramatically amplified the insulinotropic effect of 25 mM-K+ or 5 microM-A23187 stimulation. The amplified insulin-secretory response to K+, but not to A23187, was abolished by inclusion of nitrendipine during the perifusion.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- W S Zawalich
- Yale University School of Nursing, New Haven, CT 06536-0740
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29
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Hedeskov CJ, Thams P, Gembal M, Malik T, Capito K. Characteristics of phosphoinositide-specific phospholipase C activity from mouse pancreatic islets. Mol Cell Endocrinol 1991; 78:187-95. [PMID: 1663877 DOI: 10.1016/0303-7207(91)90122-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In pancreatic islets the bulk of phosphoinositide-specific phospholipase C (PI-PLC) activity was cytosolic. The soluble enzyme was activated by submicromolar concentrations of Ca2+, independent of calmodulin. It was unaffected by glucose and a series of glycolytic intermediates, including glyceraldehyde 3-phosphate. These observations lend support to the hypothesis that glucose-stimulated inositol triphosphate production in islets may be secondary to and provoked by glucose-mediated Ca2+ influx. All four pyridine nucleotides stimulated PI-PLC. Phosphatidylinositol hydrolysis was also stimulated by dioleine and arachidonic acid, and by the polyamines, putrescine and spermine. Phosphatidylinositol hydrolysis was inhibited by chlorpromazine, tetracaine, ATP, 5'-AMP, inorganic pyrophosphate and by phosphatidylinositol 4,5-bisphosphate, phosphatidylcholine and phosphatidylserine--but not affected by phosphatidylethanolamine. The cyclic nucleotides, cAMP and cGMP had no effect on the enzyme, and GTP-gamma-S did not activate the enzyme event at very low Ca2+ concentrations. The diglyceride lipase inhibitor, RHC 80267, and the cyclooxygenase inhibitor, indomethacin, had no effect on PI-PLC activity.
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Affiliation(s)
- C J Hedeskov
- Department of Biochemistry A, Panum Institute, University of Copenhagen, Denmark
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30
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Senisterra GA, Gagliardino JJ, Disalvo EA. Effect of insulin on the lytic action of lysophosphatidylcholine in lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1064:148-54. [PMID: 2025633 DOI: 10.1016/0005-2736(91)90421-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The effect of insulin on the bilayer properties of dimyristoylphosphatidylcholine liposomes at the gel and the liquid crystalline state was measured by differential scanning calorimetry and absorbance at 450 nm. It is found that insulin promotes a decrease in the enthalpy of the gel-liquid crystalline transition without displacing the transition temperature. Under these conditions the lytic action of monomyristoylphospatidylcholine is enhanced, decreasing the critical lytic concentrations to values comparable to the bilayer at the gel state. The effect of the lysoderivate on liposomes in contact with increasing concentrations of insulin promotes a reorganization of the lipids into smaller particles as inferred from fluorescence dequenching, turbidity and exclusion chromatography assay. It is concluded that the action of lysoderivates can be enhanced, at temperatures above the transition temperature, by proteins that without spanning the lipid bilayers can perturb the bilayer interface.
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Affiliation(s)
- G A Senisterra
- Instituto de Investigaciones Fisicoquimicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, UNLP, La Plata, Argentina
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31
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Gagliardino JJ, Krinks MH, Gagliardino EE. Identification of the calmodulin-regulated protein phosphatase, calcineurin, in rat pancreatic islets. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1091:370-3. [PMID: 1848110 DOI: 10.1016/0167-4889(91)90202-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The aim of this work was the identification of the calmodulin-stimulated protein phosphatase, calcineurin, in rat pancreatic islets. For this purpose, a high-affinity calcineurin antibody and the Western blotting technique were used to detect the presence of calcineurin in freshly collagenase-isolated islets. The calcineurin content detected by this method was about 0.30 ng islet (approx. 0.07% of the total islet protein). The subunit composition and Mr of islet calcineurin were similar to those of bovine brain calcineurin. Incubation of nitrocellulose membranes of the Western blotting, containing the islet protein fractions, with 125I-labeled calmodulin and 45Ca2+ demonstrated that the A subunit bound calmodulin, while the B subunit bound Ca2+. The presence of calcineurin in the islets of Langerhans would suggest its possible participation, as a counterpart of the kinases effect, in the regulatory mechanism of insulin secretion.
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Affiliation(s)
- J J Gagliardino
- CENEXA-Centro de Endocrinología Experimental y Aplicada (UNLP-CONICET), Facultad de Ciencas Médicas, La Plata, Argentina
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32
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Persaud SJ, Jones PM, Howell SL. Glucose-stimulated insulin secretion is not dependent on activation of protein kinase A. Biochem Biophys Res Commun 1990; 173:833-9. [PMID: 2176491 DOI: 10.1016/s0006-291x(05)80862-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The involvement of cyclic AMP-dependent protein kinase A (PKA) in the exocytotic release of insulin from rat pancreatic islets was investigated using the Rp isomer of adenosine 3',5'-cyclic phosphorothioate (Rp-cAMPS). Preincubation of electrically permeabilised islets with Rp-cAMPS (1 mM, 1 h, 4 degrees C) inhibited cAMP-induced phosphorylation of islet proteins of apparent molecular weights in the range 20-90 kDa, but did not affect basal (50 nM Ca2+) nor Ca2(+)-stimulated (10 microM) protein phosphorylation. Similarly, Rp-cAMPS (500 microM) inhibited both cAMP- (100 microM) and 8BrcAMP-induced (100 microM) insulin secretion from electrically permeabilised islets without affecting Ca2(+)-stimulated (10 microM) insulin release. In intact islets, Rp-cAMPS (500 microM) inhibited forskolin (1 microM, 10 microM) potentiation of insulin secretion, but did not significantly impair the insulin secretory response to a range of glucose concentrations (2-20 mM). These results suggest that cAMP-induced activation of PKA is not essential for either basal or glucose-stimulated insulin secretion from rat islets.
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Affiliation(s)
- S J Persaud
- Biomedical Sciences Division, King's College London, Kensington, U.K
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33
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Lindsay MA, Bungay PJ, Griffin M. Transglutaminase involvement in the secretion of insulin from electropermeabilised rat islets of Langerhans. Biosci Rep 1990; 10:557-61. [PMID: 1707691 DOI: 10.1007/bf01116616] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Ca(2+)-Induced insulin release from electropermeabilised islets is inhibited by the transglutaminase inhibitors monodansylcadaverine, glycine methylester, methylamine and cystamine but not by the control compounds dimethyl monodansylcadaverine and sarcosine methylester which lack the primary amine group. Neither monodansylcadaverine nor glycine methylester inhibited insulin secretion induced by either cAMP or the phorbol ester PMA at basal levels (10 nM) of Ca2+. These data provide further evidence for the involvement of transglutaminase in Ca2+ induced insulin secretion, they also suggest that insulin secretion induced by either cAMP or PMA may act in part by a mechanism independent of that induced by Ca2+.
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Affiliation(s)
- M A Lindsay
- Dept. of Life Sciences, Nottingham Polytechnic, UK
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Arkhammar P, Nilsson T, Welsh M, Welsh N, Berggren PO. Effects of protein kinase C activation on the regulation of the stimulus-secretion coupling in pancreatic beta-cells. Biochem J 1989; 264:207-15. [PMID: 2690820 PMCID: PMC1133565 DOI: 10.1042/bj2640207] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Effects of protein kinase C (PKC) activation on the insulin-secretory process were investigated, by using beta-cell-rich suspensions obtained from pancreatic islets of obese-hyperglycaemic mice. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is known to activate PKC directly, the muscarinic-receptor agonist carbamoylcholine and high glucose concentration enhanced the phosphorylation of a specific 80 kDa PKC substrate in the beta-cells. At a non-stimulatory glucose concentration, 10 nM-TPA increased insulin release, although there were no changes in either the cytoplasmic free Ca2+ concentration ([Ca2+]i) or membrane potential, as measured with the fluorescent indicators quin-2 and bisoxonol respectively. At a stimulatory glucose concentration TPA caused a lowering in [Ca2+]i, whereas membrane potential was unaffected. Despite the decrease in [Ca2+]i, there was a large stimulation of insulin release. Addition of TPA lowered [Ca2+]i also in beta-cells stimulated by tolbutamide or high K+, although to a lesser extent than in those stimulated by glucose. There was no effect of TPA on either Ca2+ buffering or the ability of Ins(1,4,5)P3 to release Ca2+ in permeabilized beta-cells. However, the phorbol ester inhibited the rise in [Ca2+]i in response to carbamoylcholine, which stimulates the formation of InsP3, in intact beta-cells. Down-regulation of PKC influenced neither glucose-induced insulin release nor the increase in [Ca2+]i. Hence, although PKC activation is of no major importance in glucose-stimulated insulin release, this enzyme can serve as a modulator of the glucose-induced insulin-secretory response. Such a modulation involves mechanisms promoting both amplification of the secretory response and lowering of [Ca2+]i.
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Affiliation(s)
- P Arkhammar
- Department of Medical Cell Biology, Uppsala University, Sweden
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35
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Hughes SJ, Chalk JG, Ashcroft SJ. Effect of secretagogues on cytosolic free Ca2+ and insulin release at different extracellular Ca2+ concentrations in the hamster clonal beta-cell line HIT-T15. Mol Cell Endocrinol 1989; 65:35-41. [PMID: 2673890 DOI: 10.1016/0303-7207(89)90162-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We have examined the relationship between extracellular Ca2+, cytosolic free Ca2+ and insulin release in the clonal beta-cell line HIT-T15. Glucose-stimulated insulin release was dependent on the extracellular Ca2+ concentration in a dose-related manner; the threshold medium Ca2+ concentration for glucose-stimulated insulin release was 0.5 mM. Both forskolin and 12-O-tetradecanoylphorbol 13-acetate (TPA) increased insulin release in the presence of glucose at all extracellular Ca2+ concentration tested (0.1-2.5 mM) but not in the absence of Ca2+. Thus, the threshold medium Ca2+ concentration for glucose-stimulated insulin release was reduced to 0.1 mM by forskolin or TPA. Step-wise increases in the medium Ca2+ concentration in the presence of an initiator of insulin release resulted in a dose-related increase in cytosolic free Ca2+. In the presence of 10 mM glucose, cytosolic free Ca2+ in HIT cells was increased from 60 +/- 5 nM in Ca2+-free medium to 290 +/- 46 nM in medium containing 2.5 mM Ca2+. The effects of increasing extracellular Ca2+ in the presence of 40 mM K+ were similar but considerably more pronounced. Inclusion of either TPA or forskolin in the incubation medium had no significant effect on the steady-state cytosolic free Ca2+ levels in the absence of glucose but in the presence of 10 mM glucose forskolin caused modest (11-18%) increases in steady-state cytosolic free Ca2+ levels at extracellular Ca2+ concentrations of 0.25 mM or above. In contrast, in the presence of glucose TPA significantly reduced the steady-state levels of cytosolic free Ca2+ by 17-21% at extracellular Ca2+ concentrations of 0.25 mM or above. These data provide further evidence that insulin release mediated by activation of beta-cell protein kinases involves primarily an increase in sensitivity of the secretory system to intracellular Ca2+.
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Affiliation(s)
- S J Hughes
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, U.K
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36
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Safayhi H, Kühn M, Koopmann I, Ammon HP. CGS 9343B and W7 (calmodulin antagonists) inhibit KCl-induced increase in cytosolic free calcium and insulin secretion of RINm5F cells. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1989; 339:8-13. [PMID: 2657441 DOI: 10.1007/bf00165119] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
CGS 9343B:1,3-Dihydro-1-[1-[4-methyl-4H,6H-pyrrolo[1,2-a]-[4,1] benzoxazepin-4-yl)methyl)-4-piperidinyl]-2H-benzimidazol-2-o ne maleate and W7:N-6(aminohexyl)-5-chloro-1-naphthalenesulfonamide) are calmodulin antagonists with different specificities. The effects of CGS 9343B and W7 on cytosolic free calcium concentration ([ Ca2+]i) and insulin release were investigated in rat insulinoma cells (RINm5F). As measured with the Quin-2 technique, preincubation with CGS 9343B (0.3-10 microM) and W7 (5-50 microM) concentration dependently decreased KCl (25 mM)-mediated accumulation of cytosolic calcium. Both, CGS 9343B (10 microM) and W7 (50-100 microM) almost abolished the alanine- and KCl-induced increase in [Ca2+]i and significantly inhibited KCl (25 mM)- and alanine (10 mM)-mediated insulin release. W5 (100 microM), the chlorine-deficient analogue of W7 with decreased affinity for calmodulin, did not inhibit the KCl-induced increase in [Ca2+]i and enhanced basal and KCl-mediated insulin release by 56% and 189%, respectively. Our data suggest that CGS 9343B and W7 inhibit the depolarization-induced calcium uptake and subsequent increase in [Ca2+]i.
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Affiliation(s)
- H Safayhi
- Department of Pharmacology, University of Tübingen, Federal Republic of Germany
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37
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Jones PM, Salmon DM, Howell SL. Protein phosphorylation in electrically permeabilized islets of Langerhans. Effects of Ca2+, cyclic AMP, a phorbol ester and noradrenaline. Biochem J 1988; 254:397-403. [PMID: 2845950 PMCID: PMC1135091 DOI: 10.1042/bj2540397] [Citation(s) in RCA: 135] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The incorporation of 32P from [gamma-32P]ATP into intracellular proteins was studied in electrically permeabilized rat islets of Langerhans. Ca2+ (10 microM), cyclic AMP (100 microM) and a protein kinase C-activating phorbol ester, phorbol 13-myristate 12-acetate (PMA; 100 nM) produced marked changes in the phosphorylation state of a number of proteins in permeabilized islets after incubation for 1 min at 37 degrees C. Ca2+ modified the effects of cyclic AMP and PMA on protein phosphorylation. Noradrenaline (10 microM) had no detectable effects on Ca2+-dependent protein phosphorylation, but significantly inhibited Ca2+-induced insulin secretion from electrically permeabilized islets. These results suggest that electrically permeabilized islets offer a useful model in which to study rapid events in protein phosphorylation as a mechanism of stimulus-secretion coupling. If the rapid Ca2+-induced effects on protein phosphorylation are involved in the control of insulin secretion, the results of this study also imply that part of the catecholamine inhibition of insulin secretion occurs at a stage in the secretory pathway beyond the activation of the regulated protein kinases.
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Affiliation(s)
- P M Jones
- Department of Physiology, King's College London, U.K
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38
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Metz SA. Dantrolene-induced inhibition of insulin release. A mechanism independent of effects on calcium fluxes. Biochem Pharmacol 1988; 37:2237-45. [PMID: 2454111 DOI: 10.1016/0006-2952(88)90587-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Dantrolene is felt to inhibit the release of Ca2+ from vesicular stores but only in response to certain stimuli; the mechanism responsible for its effects is unclear. Since our recent studies implicated arachidonic acid and other polyunsaturated fatty acids in Ca2+ mobilization and insulin release from pancreatic islets, we have now examined the effect of dantrolene on fatty acid-induced 45Ca2+ efflux and insulin release. Dantrolene inhibited insulin secretion induced by exogenous unsaturated fatty acids as well as that caused by endogenous fatty acids (generated via the exogenous provision of pancreatic phospholipase A2, or by p-hydroxymercuribenzoic acid, which prevents the reacylation of free fatty acids). In contrast, the effects of 50 mM K+, 2 mM BaCl2, 1 mM isobutylmethylxanthine or lysophosphatidylcholine were not impaired, suggesting that dantrolene does not inhibit nonspecifically the influx, mobilization or cellular effects of Ca2+, or poison exocytosis in general. However, dantrolene did reduce insulin secretion triggered by 12-O-tetradecanoylphorbol-13-acetate, mezerein or exogenous phospholipase C, all of which can activate protein kinase C; this inhibition was not accompanied by alterations in 45Ca2+ efflux. Furthermore, the 45Ca2+ efflux induced by phospholipase A2 or p-hydroxymercuribenzoic acid was not reduced by dantrolene. We conclude that the insulin secretion stimulated by unsaturated fatty acids involves two effects (one on Ca2+ fluxes, and one independent of Ca2+ mobilization). Dantrolene, in turn, may selectively probe such fatty acid-dependent insulin release; its inhibitory effect is predominantly, if not totally, independent of effects on Ca2+ fluxes, and may involve the inhibition of the effects of protein kinase C on exocytosis.
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Affiliation(s)
- S A Metz
- Research Service, Denver VA Medical Center, CO 80220
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39
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Owen RA, Bungay PJ, Hussain M, Griffin M. Transglutaminase-catalysed cross-linking of proteins phosphorylated in the intact glucose-stimulated pancreatic beta-cell. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 968:220-30. [PMID: 2893644 DOI: 10.1016/0167-4889(88)90011-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Incubation of intact islets in the presence of [32P]Pi and stimulatory levels of glucose followed by separation of phosphorylated islet proteins by SDS-polyacrylamide gel electrophoresis revealed the presence of a high molecular weight phosphopolymer which did not transverse a 3% (w/v) acrylamide gel. The majority of this phosphopolymer (approx. 70%) was present in the 600 x g sedimented fraction of islet homogenates. Islet homogenates obtained from intact islets previously incubated with [32P]Pi and stimulatory levels of glucose when incubated under conditions that activated the islet transglutaminase resulted in an increase in the amount of phosphopolymer present in the 600 x g sedimented fraction. Inhibitors of transglutaminase activity which are known to inhibit glucose-stimulated insulin release led to a significant reduction in the fraction of phosphopolymer present in the glucose-stimulated intact islet. These findings suggest that protein cross-linking and phosphorylation reactions may be closely linked in the pancreatic beta-cell.
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Affiliation(s)
- R A Owen
- Department of Life Sciences, Trent Polytechnic, Clifton, Nottingham, U.K
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40
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Hughes SJ, Ashcroft SJ. Effects of a phorbol ester and clomiphene on protein phosphorylation and insulin secretion in rat pancreatic islets. Biochem J 1988; 249:825-30. [PMID: 3281655 PMCID: PMC1148781 DOI: 10.1042/bj2490825] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The potentiation of glucose-stimulated insulin release induced by 100 nM-12-O-tetradecanoylphorbol 13-acetate (TPA) was inhibited by clomiphene, an inhibitor of protein kinase C (PK C), in a dose-dependent manner. Clomiphene at concentrations up to 50 microM had a modest inhibitory action (27%) on insulin release stimulated by 10 mM-glucose alone, but had no effect on the potentiation of insulin release induced by forskolin. Islet PK C activity, associated with a particulate fraction, was stimulated maximally by 100 nM-TPA. This stimulation was blocked by clomiphene in a dose-dependent manner, with 50% inhibition at 30 microM. Incubation of intact islets with TPA after preincubation with [32P]Pi and 10 mM-glucose to label intracellular ATP resulted primarily in enhanced phosphorylation of a 37 kDa protein (mean value, +/- S.E.M., 36,700 +/- 600 Da; n = 7). This increased phosphorylation was blocked by the simultaneous inclusion of clomiphene. Subcellular fractionation revealed the presence of the 37 kDa phosphoprotein in a 24,000 g particulate fraction of islet homogenates. Neither clomiphene nor TPA affected the rate of glucose oxidation by islets. These results show that the phosphorylation state of a 37 kDa membrane protein parallels the modulation of insulin release induced by TPA and clomiphene and support a role for PK C in the insulin-secretory mechanism.
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Affiliation(s)
- S J Hughes
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, U.K
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41
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Stimulus-Secretion Coupling in the Pancreatic B Cell. CURRENT TOPICS IN NEUROENDOCRINOLOGY 1988. [DOI: 10.1007/978-3-642-73495-3_8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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42
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Yamatani K, Sato N, Wada K, Suda K, Wakasugi K, Ogawa A, Takahashi K, Sasaki H, Hara M. Two types of hormone-responsive adenylate cyclase in the rat liver. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 931:180-7. [PMID: 2444265 DOI: 10.1016/0167-4889(87)90205-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We have demonstrated the existence of two types of hormone-responsive adenylate cyclase in the isolated perfused rat liver. One, less abundant, is linked to glycogenolysis and the other is not. Glucagon stimulates mainly the glycogenolysis-linked fraction and, to a lesser extent, the fraction which is not linked to glycogenolysis. The suppressive effect of insulin is specific for the glucagon-responsive adenylate cyclase and is inhibited by 3-isobutyl-1-methylxanthine (IBMX). However, this mechanism can explain only partly the ability of insulin to suppress glycogenolysis, and is not observed when cAMP is increased sufficiently by glucagon. Secretin-responsive adenylate cyclase is not linked to glycogenolysis and is suppressed specifically by oxymetazoline. The capacity of this suppressive effect is large and not inhibited by IBMX. These results suggest that there is a functional compartmentalization of cAMP within the hepatocyte or among hepatocytes.
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Affiliation(s)
- K Yamatani
- Third Department of Internal Medicine, Yamagata University School of Medicine, Japan
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43
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Hammonds P, Schofield PN, Ashcroft SJ, Sutton R, Gray DW. Regulation and specificity of glucose-stimulated insulin gene expression in human islets of Langerhans. FEBS Lett 1987; 223:131-7. [PMID: 3311808 DOI: 10.1016/0014-5793(87)80523-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The insulin response of cultured human islets of Langerhans was measured at both mRNA and polypeptide levels in response to natural and pharmacological stimuli. We report a dosage dependent stimulation of both mRNA levels and insulin secretion by extracellular glucose, and present evidence that islet responsiveness can be divided into two temporal phases: an early response, apparently under post-transcriptional control, and a late phase in which insulin messenger accumulates. Although glucose effects in man are similar to rodents, there are important differences, especially with respect to modulation of glucose stimulation by activators of beta-cell protein kinases.
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Affiliation(s)
- P Hammonds
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, England
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44
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Henquin JC, Bozem M, Schmeer W, Nenquin M. Distinct mechanisms for two amplification systems of insulin release. Biochem J 1987; 246:393-9. [PMID: 2825637 PMCID: PMC1148288 DOI: 10.1042/bj2460393] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The mechanisms whereby activation of the cyclic AMP-dependent protein kinase A or the Ca2+-phospholipid-dependent protein kinase C amplifies insulin release were studied with mouse islets. Forskolin and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) were used to stimulate adenylate cyclase and protein kinase C respectively. The sulphonylurea tolbutamide was used to initiate insulin release in the presence of 3 mM-glucose. Tolbutamide alone inhibited 86Rb+ efflux, depolarized beta-cell membrane, triggered electrical activity, accelerated 45Ca2+ influx and efflux and stimulated insulin release. Forskolin alone only slightly inhibited 86Rb+ efflux, but markedly increased the effects of tolbutamide on electrical activity, 45Ca2+ influx and efflux, and insulin release. In the absence of Ca2+, only the inhibition of 86Rb+ efflux persisted. TPA (100 nM) alone slightly accelerated 45Ca2+ efflux and insulin release without affecting 45Ca2+ influx or beta-cell membrane potential. It increased the effects of tolbutamide on 45Ca2+ efflux and insulin release without changing 86Rb+ efflux, 45Ca2+ influx or electrical activity. Omission of extracellular Ca2+ suppressed all effects due to the combination of TPA and tolbutamide, but not those of TPA alone. Though ineffective alone, 10 nM-TPA amplified the releasing action of tolbutamide without affecting its ionic and electrical effects. In conclusion, the two amplification systems of insulin release involve at least partially distinct mechanisms. The cyclic AMP but not the protein kinase C system initiating signal (Ca2+ influx) triggered by the primary secretagogue.
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Affiliation(s)
- J C Henquin
- Unité de Diabétologie et Nutrition, Faculté de Médecine, Université Catholique de Louvain, Bruxelles
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45
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Hii CS, Jones PM, Persaud SJ, Howell SL. A re-assessment of the role of protein kinase C in glucose-stimulated insulin secretion. Biochem J 1987; 246:489-93. [PMID: 3318809 PMCID: PMC1148300 DOI: 10.1042/bj2460489] [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: 01/05/2023]
Abstract
Isolated rat islets of Langerhans which had been pretreated with 200 nM-phorbol 12-myristate 13-acetate (PMA) for 20-24 h, a treatment reported in other cell types to deplete cells of protein kinase C activity, were found not to contain detectable Ca2+/phospholipid-dependent protein kinase activity. These islets did not secrete insulin in response to a subsequent exposure to PMA (0.1 or 1 microM) during a 30 min incubation, although insulin secretion could be stimulated by 20 mM-glucose, a response which was enhanced by 20 microM-forskolin. PMA-pretreated islets that had been permeabilized by high-voltage discharge showed unimpaired secretory responses to an increase in Ca2+ concentration, cyclic AMP and forskolin. These results suggest that (i) pretreatment of islets with tumour-promoting phorbol esters may be a useful means of investigating the role of protein kinase C in stimulus-secretion coupling in the pancreatic beta-cell and (ii) protein kinase C may not play an essential role in glucose-induced insulin secretion.
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Affiliation(s)
- C S Hii
- Department of Physiology, Kings College London, University of London, U.K
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46
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Hammonds P, Schofield PN, Ashcroft SJ. Glucose regulates preproinsulin messenger RNA levels in a clonal cell line of simian virus 40-transformed B cells. FEBS Lett 1987; 213:149-54. [PMID: 3030804 DOI: 10.1016/0014-5793(87)81481-3] [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: 01/03/2023]
Abstract
In HIT-T15 cells grown in the absence of glucose, Northern blot analysis of total RNA revealed a major 0.5 kb preproinsulin (ppI) mRNA transcript which co-migrated with the mature transcript from a human insulinoma. In 4 h tissue cultures, glucose (2-20 mM) stimulated HIT cell ppI mRNA levels in a markedly dose-dependent manner. Glucose-stimulated ppI mRNA was (i) inhibited by actinomycin D, suggesting that regulation may be in part transcriptional, and (ii) potentiated by agents known to activate B cell protein kinases. HIT cells represent a unique model for investigating long term regulation of insulin gene expression and biosynthesis.
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47
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SWANSTON-FLATT SARAK, FLATT PETERR. ACUTE AND LONG-TERM EFFECTS OF GLUCOSE ON THE FUNCTION OF TRANSPLANTABLE RAT INSULINOMA CELLS MAINTAINED IN TISSUE CULTURE . Biomed Res 1987. [DOI: 10.2220/biomedres.8.215] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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48
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Henquin JC, Meissner HP. Cyclic adenosine monophosphate differently affects the response of mouse pancreatic beta-cells to various amino acids. J Physiol 1986; 381:77-93. [PMID: 3040964 PMCID: PMC1182966 DOI: 10.1113/jphysiol.1986.sp016314] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
1. The membrane potential of mouse beta-cells was measured in parallel with 86Rb+ efflux and insulin release from mouse islets during stimulation by three types of amino acids and modulation of their effects by glucose and cyclic adenosine monophosphate (cyclic AMP) (forskolin being used to activate the adenylate cyclase). 2. In the absence of glucose, alanine and arginine accelerated 86Rb+ efflux, whereas leucine decreased it. They all depolarized the beta-cell membrane and slightly increased insulin release. Forskolin had little effect on 86Rb+ efflux, consistently potentiated insulin release but induced electrical activity only in the presence of leucine. 3. The effects of the three amino acids on 86Rb+ efflux and beta-cell membrane potential were not qualitatively altered by a non-stimulatory concentration of glucose (3 mM). However, the release of insulin induced by leucine alone or with forskolin was markedly amplified, in contrast to that of alanine or arginine, which was inhibited. 4. In the presence of a threshold concentration of glucose (7 mM), the three amino acids accelerated 86Rb+ efflux and depolarized the beta-cell membrane. With alanine and arginine, spike activity was transiently observed and coincided with a short-lived increase in insulin release. With leucine, slow waves with superimposed bursts of spikes occurred and were accompanied by a sustained release of insulin. Forskolin alone also triggered slow waves and bursts of spikes, and increased insulin release. Both effects were larger in the presence of arginine, but not in the presence of alanine. Forskolin considerably increased the electrical and secretory effects of leucine. 5. A higher concentration of glucose (10 mM) induced slow waves with bursts of spikes in all cells and stimulated insulin release. Alanine, arginine and leucine increased 86Rb+ efflux, electrical activity and insulin release. However, the changes produced by the three amino acids displayed different time course, amplitude and characteristics. Forskolin potentiated insulin release and electrical activity induced by glucose alone. These effects were not augmented by alanine, but markedly amplified by arginine or leucine. 6. Several conclusions can be drawn from this study. The three types of amino acids depolarize the beta-cell membrane by different mechanisms and produce distinct patterns of electrical activity. Slow waves with bursts of spikes occur only if a decrease in K+ permeability contributes to the depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
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49
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Abstract
The Ca ion plays a central role in the control of the regulated pathway of exocytotic secretion in eukaryote cells. Most secretagogues either directly or indirectly raise cytosolic free Ca levels which in turn affects granule biogenesis, contractile events, gel/sol transition in intracellular matrix and membrane fusion events occurring at exocytosis. Many of these responses are mediated by Ca-binding proteins among which calmodulin and protein kinase C have received prominent attention. Studies of the nature and inter-relationship of proteins which undergo Ca-dependent association with intracellular membranes in secretory tissue reveal that there may be further Ca-binding proteins in these cells which act as intracellular transducers of the Ca signal during secretion.
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50
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Abstract
The occurrence of polyamine-stimulated protein kinase (casein kinase II) in cytosol of mouse pancreatic islets was investigated. Islet protein phosphorylation was enhanced by spermidine, spermine, lysine-rich histone and polylysine; the major endogenous substrates in the cytosol were three proteins of Mr 50,000, 55,000 and 100,000. Cadaverine and putrescine were without effects. A Mr 100,000 protein is a major substrate for Ca2+-calmodulin-dependent protein kinase, and Mr 50,000 and 55,000 proteins are substrates for cyclic adenosine 3',5'-cyclic monophosphate (AMP) dependent protein kinase in mouse islets. However, neither cyclic-AMP-dependent protein kinase inhibitor nor trifluoperazine inhibited polyamine-enhanced protein phosphorylation. Both basal and polyamine-enhanced protein phosphorylation patterns were identical when either [gamma-32P] adenosine 5'-triphosphate (ATP) or [gamma-32P] guanosine 5'-triphosphate (GTP) was used as phosphate donors, indicative of the presence of a polyamine-stimulated casein kinase II in pancreatic islets. It is suggested that polyamines and polyamine-enhanced casein kinase II activity may have an important role in regulation of protein phosphorylation in pancreatic islets.
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