scholarly journals Differential effects of Ca2+-calmodulin on adenylate cyclase activity cyclase activity in mouse and rat pancreatic islets

1982 ◽  
Vol 206 (1) ◽  
pp. 97-102 ◽  
Author(s):  
P Thams ◽  
K Capito ◽  
C J Hedeskov
Keyword(s):  
Adenylate Cyclase ◽  
Pancreatic Islets ◽  
Specific Inhibitor ◽  
Particulate Fraction ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Mouse Islets

The effects of Ca2+-calmodulin on adenylate cyclase activity in EGTA-washed, 27000 g particulate fractions of mouse and rat pancreatic islets were studied. Ca2+ (10 microM)-calmodulin (1 microM) stimulated adenylate cyclase activity 53.1 +/- 5.2 (N = 6)% in the particulate fraction of rat islets. Trifluoperazine (50 microM), a specific inhibitor of calmodulin, inhibited the Ca2+-calmodulin activation of the adenylate cyclase activity of this fraction of rat islets. These results confirm previous reports dealing with Ca2+-Calmodulin and rat islet adenylate cyclase [Valverde, Vandermeers. Anjaneyulu & Malaisse (1979) Science 206, 225-227; Sharp, Wiedenkeller, Kaelin, Siegel & Wollheim (1980) Diabetes 29, 74-77]. In contrast, however, Ca2+ (1-100 microM)-calmodulin (1-10 microM) did not stimulate the adenylate cyclase activity in the EGTA-washed particulate fraction of mouse islets, and trifluoperazine (50 microM) did not inhibit the adenylate cyclase activity of this fraction of mouse islets, although some remaining calmodulin [0.18 +/- 0.05 (n = 3) microgram/mg of protein] could be demonstrated. GTP (10 microM) enhanced islet adenylate cyclase activity considerably, but did not confer any sensitivity towards Ca2+-calmodulin on mouse islet adenylate cyclase. The results question the role of calmodulin in the Ca2+-dependent rise in cyclic AMP evoked by glucose in pancreatic islets.

Inhibitory effect of clonidine upon adenylate cyclase activity, cyclic AMP production, and insulin release in rat pancreatic islets

1984 ◽  
Vol 4 (6) ◽  
pp. 511-521 ◽  
Author(s):  
P. Garcia-Morales ◽  
S. P. Dufrane ◽  
A. Sener ◽  
I. Valverde ◽  
W. J. Malaisse
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Inhibitory Action ◽  
Fold Increase ◽  
Inhibitory Effect ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rat Pancreatic Islets

Conflicting opinions were recently expressed concerning the possible effect of α2-adrenergic agonists upon cyclic AMP production in pancreatic islets. In the present: study, clonidine inhibited glucose-induced insulin release from rat pancreatic islets, this inhibitory effect being abolished by idazoxan. Clonidine did not suppress the capacity of forskolin to augment glucose-induced insulin release. In a particulate subcellular fraction derived from the islets, adenylate cyclase was activated by calmodulin (in the presence of Ca2+), NaF, GTP, L-arginine, and forskolin, and slightly inhibited by clonidine. The inhibitory action of clonidine upon basal adenylate cyclase activity was more pronounced in islet crude homogenates. The inhibitory effect of clonidine was antagonized by forskolin whether in the particulate fraction or crude homogenate. At variance with the modest effects of glucagon, D-glucose, L-arginine, or a tumor-promoting phorbol ester upon cyclic AMP production by intact islets, forskolin caused a six-fold increase in cyclic AMP production. Clonidine inhibited cyclic AMP production by intact islets, whether in the absence or presence of forskolin. It is proposed that the inhibitory action of clonidine upon insulin release is attributable, in part at least, to inhibition of adenylate cyclase.

The Role of Guanine Nucleotides in Regulation of Adenylate Cyclase Activity

1981 ◽  
pp. 635-665
Author(s):  
ALLEN M. SPIEGEL ◽  
ROBERT W. DOWNS ◽  
MICHAEL A. LEVINE ◽  
MORTON J. SINGER ◽  
WOLFGANG KRAWIETZ ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
Guanine Nucleotides ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity

Age-dependent mechanical and biochemical responses to glucagon

1976 ◽  
Vol 230 (6) ◽  
pp. 1590-1593 ◽  
Author(s):  
G Ahumada ◽  
BE Sobel ◽  
WF Friedman
Keyword(s):  
Adenylate Cyclase ◽  
Ventricular Myocardium ◽  
Fetal Tissue ◽  
Particulate Fraction ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Glucagon Receptor ◽  
Tension Development ◽  
Receptor Sites ◽  
Age Dependent

The age-dependent relationships between glucagon-induced alterations in myocardial mechanics and adenylate cyclase activity in fetal and newborn lambs and adult sheep were evaluated. Glucagon substantially augmented the force of contraction of ventricular myocardium isolated from the adult but not from the fetus or newborn. Similarly, substantial increases in the spontaneous frequency of contraction and tension were observed in adult atrial strips, but not in the fetus or newborn. Comparable activities of phosphodiesterase were observed in extracts from fetal and adult myocardium and were unaltered by the addition of glucagon. Adenylate cyclase activity in adult myocardial homogenate and particulate fractions was comparable to that of fetal tissue. Glucagon stimulation of the particulate fraction produced no change in fetal adenylate cyclase activity whereas a 43% increase in activity was observed in preparations from adult tissue. Sodium fluoride and epinephrine augmented adenylate cyclase activity in both fetal and adult myocardium. Thus, glucagon produced age-dependent, parallel changes in heart rate, active tension development, and particulate fraction adenylate cyclase activity, suggesting that these chronotropic and inotropic responses are indeed mediated by adenylate cyclase and that lack of response in the fetus reflects the absence of mature glucagon receptor sites.

scholarly journals Role of pertussis toxin-sensitive guanosine triphosphate-binding proteins in the response of erythroblasts to erythropoietin

Blood ◽  
1991 ◽  
Vol 77 (3) ◽  
pp. 486-492 ◽  
Author(s):  
BA Miller ◽  
K Foster ◽  
JD Robishaw ◽  
CF Whitfield ◽  
L Bell ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
Pertussis Toxin ◽  
Binding Proteins ◽  
Binding Protein ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Guanosine Triphosphate ◽  
Gtp Binding Protein ◽  
Gtp Binding

Abstract Human progenitor-derived erythroblasts have been recently shown to respond to erythropoietin (Epo) with an increase in intracellular free calcium concentration [Cac]. To explore the role of guanosine triphosphate (GTP)-binding proteins in mediating the rise in [Cac], single day 10 erythroid burst forming unit (BFU-E)-derived erythroblasts loaded with Fura-2 were pretreated with pertussis toxin (PT), stimulated with Epo, and [Cac] measured over 18 minutes with fluorescence microscopy coupled to digital video imaging. The [Cac] increase in day 10 erythroblasts stimulated with Epo was blocked by pretreatment with PT in a dose-dependent manner but not by heat- inactivated PT. These observations provided strong evidence that a PT- sensitive GTP-binding protein is involved. To further characterize the GTP-binding protein, day 10 erythroblast membrane preparations were solubilized, electrophoresed, and immunoblotted with antibodies specific for the known PT-sensitive G-protein subunits: the three subtypes of Gia (1,2, and 3) and Goa, Gia1 or Gia3 and Gia2 were identified but no Goa was found. To examine the influence of Epo on adenylate cyclase activity, day 10 erythroblasts were initially treated with Epo, isolated membrane preparations made, and cyclic adenosine monophosphate (cAMP) production by adenylate cyclase in membrane preparations in the presence of theophylline measured. Epo did not inhibit but significantly stimulated adenylate cyclase activity. However, the mechanism of increase of [Cac] appears to be independent of adenylate cyclase stimulation because treatment of erythroblasts with the cell-permeant dibutyryl cAMP failed to increase [Cac]. In summary, pertussis toxin blocks the increase in [Cac] in erythroblasts after Epo stimulation suggesting that this response is mediated through a pertussis toxin-sensitive GTP-binding protein. Candidate PT-sensitive GTP-binding proteins identified on day 10 erythroblasts were Gia 1, 2, or 3, but not Goa.

scholarly journals Role of prostaglandins in hypoxia-stimulated erythropoietin production

1985 ◽  
Vol 249 (1) ◽  
pp. C3-C8 ◽  
Author(s):  
A. Kurtz ◽  
W. Jelkmann ◽  
J. Pfeilschifter ◽  
C. Bauer
Keyword(s):  
Arachidonic Acid ◽  
Adenylate Cyclase ◽  
Cell Cultures ◽  
Mesangial Cells ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Cyclooxygenase Inhibitor ◽  
Erythropoietin Production ◽  
Stimulation Of

The role of prostaglandins in the mediation of hypoxia-stimulated erythropoietin (Ep) production by cultured rat renal mesangial cells was examined. It was found that an increase in prostaglandin E2 (PGE2) production accompanied the rise in Ep due to hypoxia (2% O2). The hypoxia-stimulated increase in Ep production was abolished in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M). When PGE2 (10(-6) M was added simultaneously with indomethacin, however, no diminution in hypoxia-stimulated Ep production was observed. Addition of arachidonic acid (AA, 10(-5) M), PGE2 (10(-6) M), or PGI2 (10(-4) M) enhanced Ep production under normoxic conditions (20% O2), while PGF2 alpha (10(-6) M) had no effect on Ep production. AA, PGE2, and PGI2 were found to stimulate adenosine 3',5'-cyclic monophosphate formation by the cultured mesangial cells. Enhancement of adenylate cyclase activity by forskolin (10(-5) M) also increased Ep production in the cell cultures. Our results suggest that hypoxia-stimulated Ep production by cultured mesangial cells is mediated by prostaglandins with subsequent stimulation of adenylate cyclase activity.

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