Calmodulin Activation of Adenylate Cyclase in Pancreatic Islets

Valverde, Isabel; Vandermeers, André; Anjaneyulu, Renu; Malaisse, Willy

doi:10.1126/science.225798

Cited by 236 publications

(99 citation statements)

References 26 publications

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“…This protein has recently been identified in rat islets [30,31], and the calmodulin inhibitor trifluoperazine [32] found to inhibit insulin secretion [30]. A similar Induced insulin release was also inhibited by vinblastine and colchicine.…”

Section: Discussionmentioning

confidence: 97%

Insulin secretion by a transplantable rat islet cell tumour

et al. 1981

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Summary. Investigation of the subcellular and molecular components of insulin secretion has been made difficult by the small quantities of material available. The recent development of a transplantable rat islet cell tumour of high insulin content and state of differentiation suggested a system more amenable to analysis. To validate the tumour as a model of secretion we have studied its release of insulin. In acute experiments in vitro immunoreactive insulin release was increased by leucine, glucagon, theophylline and dibutyryl cyclic AMP, though not by glucose. Leucine (20 mmol/1) plus theophylline (5 mmol/1) caused an abrupt, sustained and rapidly reversible stimulation of two-to fivefold. The response was inhibited by antagonists of cellular oxidative phosphorylation (cyanide, 2,4--dinitrophenol, antimycin A), calcium flux (EGTA, verapamil, Mg2 § calmodulin (trifluoperazine), microtubules (vinblastine, colchicine) and by adrenaline and somatostatin. These findings suggest that the tumour secretes insulin by an exocytotic mechanism similar to that of normal islet tissue. Key words: Islet cell tumour, B cell, insulin secretionThe pancreatic B cell has proved difficult to investigate at the subcellular and molecular levels. The classical strategy of subcellular fractionation, purification and reassembly has been greatly hindered by the shortage of starting material [3,4]. In this context the description recently of a transplantable rat islet cell tumour is of considerable interest. The tumour contains large amounts of insulin and consists predominantly of well-granulated cells the morphology of which closely resembles that of rat B cells [1,2].That this islet cell tumour might offer a largescale model of insulin secretion is an attractive possibility. Realisation of this potential, however, depends upon establishing that the tumour is indeed capable of the exocytosis of insulin. We here report a series of experiments in which the characteristics of insulin release by the turnout were defined. The effect of putative secretagogues, the dynamics of insulin release, and the influence of potentiators and inhibitors of secretion are described. Materials and MethodsThe islet cell tumour [1, 2] was maintained by serial subcutaneous transplantation within a colony of inbred albino NEDH strain rats [2]. BuffersTissue was handled in a Krebs Ringer solution [5] containing NaC1 115mmol/1, KC1 5.0mmol/1, NaI-ICO 3 24mmol/1, MgC12 1.0 mmol/1 and CaC12 2.5 mmol/1, freshly equilibrated with 5% CO 2 95% 02. Except where specified glucose 2.8 mmol/l, bovine plasma albumin (Armour Pharmaceuticals, Eastbourne, UK) 1.0 mg/ml, and 5.0 mmol/1 each of sodium pyruvate, monosodium glutamate and disodium fumarate were included (using 95 mmol/l NaC1 to maintain the final sodium ion concentration at 139 mmol/ 1). When individual experiments required further additions the osmolality of control buffers was balanced using sucrose.Chemicals were purchased from Fisons Scientific Apparatus, Loughborough, UK and British Drug House Chemicals, Poole,...

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Section: Discussionmentioning

confidence: 97%

Insulin secretion by a transplantable rat islet cell tumour

et al. 1981

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“…Previous work on whole islets emphasised the importance of calcium for islet adenylyl cyclase activity. Two studies [47,48] have shown that homogenates of rat isolated islets contain Ca 2+ -calmodulin-dependent AC activity. We show that the Ca 2+ -calmodulin effects interact synergistically with that of G sα .…”

Section: Discussionmentioning

confidence: 99%

Type VIII adenylyl cyclase in rat beta cells: coincidence signal detector/generator for glucose and GLP-1

et al. 2003

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Aims/hypothesis. The secretory function of pancreatic beta cells is synergistically stimulated by two signalling pathways which mediate the effects of nutrients and hormones such as glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) or glucagon. These hormones are known to activate adenylyl cyclase in beta cells. We examined the type of adenylyl cyclase that is associated with this synergistic interaction. Methods. Insulin release, cAMP production, adenylyl cyclase activity, mRNA and protein expression were measured in fluorescence-activated cell sorter-purified rat beta cells and in the rat beta-cell lines RINm5F, INS-1 832/13 and INS-1 832/2. Results. In primary beta cells, glucagon and GLP-1 synergistically potentiate the stimulatory effect of 20 mmol/l glucose on insulin release and cAMP production. Both effects are abrogated in the presence of the L-type Ca 2+ -channel blocker verapamil. The cAMP-producing activity of adenylyl cyclase in membranes from RINm5F cells is synergistically increased by Ca 2+ -calmodulin and recombinant GTP γ S-activated G sα -protein subunits. This type of regulation is characteristic for type I and type VIII AC isoforms. Consistent with this functional data, AC mRNA analysis shows abundant expression of type VI AC, four splice variants of type VIII AC and low expression level of type I AC in beta cells. Type VIII AC expression at the protein level was observed using immunoblots of RINm5F cell extracts. Conclusion/interpretation. This study identifies type VIII AC in insulin-secreting cells as one of the potential molecular targets for synergism between GLP-1 receptor mediated and glucose-mediated signalling. [Diabetologia (2003)

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“…cAMP is formed by adenylyl cyclases in response to G s -coupled receptor agonists, such as glucagon, the incretin hormones glucagon-like peptide-1 (GLP-1) and gastric inhibitory popypeptide (GIP), as well as the neuropeptides pitutitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal popypeptide (VIP). Also glucose-stimulated islets show a modest elevation of cAMP (Charles et al, 1973;Grill and Cerasi, 1973;Hellman et al, 1974;Sharp, 1979), an effect that has been attributed to the elevation of [Ca 2+ ] i (Charles et al, 1975;Valverde et al, 1979). From the observation that purified β-cells, lacking influence from the glucagon-producing α-cells, show reduced cAMP content and impaired secretory capacity, it was suggested that cAMP has a permissive role in glucose-induced insulin release and that the effect of the sugar on cAMP content represents amplification of glucagon-induced cAMP production (Schuit and Pipeleers, 1985).…”

Section: Cyclic Ampmentioning

confidence: 99%

Oscillatory control of insulin secretion

Tengholm

Gylfe

2009

Molecular and Cellular Endocrinology

163

169

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Pulsatile insulin secretionSince insulin is the only blood glucose-lowering hormone, its secretion is essential for glucose homeostasis, and disturbances are associated with glucose intolerance and diabetes.Glucose is the major stimulus for insulin release but secretion is enhanced also by other nutrients and is under stimulatory and inhibitory control by hormones and neurotransmitters.Although the external factors are essential determinants of insulin secretion, there are also input-independent variations in hormone release. Regular oscillations of the circulating insulin concentrations in normal subjects consequently occur without accompanying changes

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Calmodulin Activation of Adenylate Cyclase in Pancreatic Islets

Cited by 236 publications

References 26 publications

Insulin secretion by a transplantable rat islet cell tumour

Insulin secretion by a transplantable rat islet cell tumour

Type VIII adenylyl cyclase in rat beta cells: coincidence signal detector/generator for glucose and GLP-1

Oscillatory control of insulin secretion

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