scholarly journals Adaptation to chemotactic cyclic AMP signals in Dictyostelium involves the G-protein

1987 ◽  
Vol 88 (4) ◽  
pp. 537-545
Author(s):  
N.V. Small ◽  
G.N. Europe-Finner ◽  
P.C. Newell
Keyword(s):  
Cyclic Amp ◽  
G Protein ◽  
Cyclic Gmp ◽  
Transduction Pathway ◽  
Adaptation Mechanism ◽  
Permeabilized Cells ◽  
Inositol 1,4,5 Trisphosphate ◽  
Gamma S ◽  
Stimulation Of

Amoebae of Dictyostelium discoideum show adaptation towards a chemotactic cyclic AMP signal. Within a few seconds of receipt of the signal they are inhibited for a period of 1–2 min from further chemotactic responses to subsequent cyclic AMP signals of similar or smaller magnitude. The site of this adaptation mechanism in the chemotactic transduction pathway was investigated by addition of components of the transduction chain (GTP analogues, myo-inositol-1,4,5-trisphosphate (InsP3) and Ca2+) to permeabilized cells followed by determination of the amount of cyclic GMP formed as a measure of the chemotactic response. This approach was made possible by finding that permeabilization of amoebae with saponin did not uncouple the cell surface cyclic AMP receptors from stimulation of cyclic GMP formation. It was found that InsP3 and Ca2+ were ‘downstream’ from the adaptation mechanism: they could trigger a cyclic GMP response in cyclic AMP-adapted amoebae but could not themselves induce adaptation. In contrast, GTP gamma S was unable to trigger a cyclic GMP response in cyclic AMP-adapted cells, although it could trigger multiple cyclic GMP responses in non-adapted cells. We deduce that the site of adaptation to cyclic AMP stimulation is at the G-protein involved in this signalling pathway. Moreover, as GTP gamma S was found to be unable to induce adaptation, we conclude that the mechanism of adaptation involves an action of the cyclic AMP receptor on the G-protein that is distinct from its commonly reported action of stimulating G-protein binding of GTP.

GTP analogues stimulate inositol trisphosphate formation transiently in Dictyostelium

1987 ◽  
Vol 87 (4) ◽  
pp. 513-518
Author(s):  
G.N. Europe-Finner ◽  
P.C. Newell
Keyword(s):  
Cyclic Amp ◽  
G Proteins ◽  
Inositol Trisphosphate ◽  
Signal Transduction Pathway ◽  
Transduction Pathway ◽  
Permeabilized Cells ◽  
Maximal Stimulation ◽  
Gamma S ◽  
Stimulation Of

Permeabilization of amoebae of Dictyostelium discoideum with saponin was found not to uncouple the chemotactic cell surface cyclic AMP receptors from inositol trisphosphate (IP3) formation, and stimulation of permeabilized amoebae with 50 nM-cyclic AMP produced peaks of IP3 at 5, 15 and 30 s in a manner comparable to that seen previously in non-permeabilized cells. The possible involvement of a GTP-binding protein (G-protein) in this IP3 signal transduction pathway was investigated by studying the effects on such permeabilized amoebae of added GTP and non-hydrolysable GTP analogues. While GDP produced only very minor effects, stimulation of the amoebae (in the absence of added cyclic AMP) with GTP or the non-hydrolysable GTP analogues GTP gamma S (guanosine 5′-O-(3-thio-triphosphate] and Gpp(NH)p (5′-guanylylimidodiphosphate) induced transient formation of IP3 in an oscillatory manner, with peaks similar in magnitude and timing to those elicited by cyclic AMP. A dose-response curve for GTP gamma S indicated a concentration for half-maximal stimulation of approximately 8 microM. When tested at 300 s after addition of GTP gamma S, the basal level of IP3 was found to be twofold elevated with shallow (presumably asynchronous) oscillations still just discernible. The significance of the IP3 oscillations elicited by GTP and its analogues is discussed in relation to the mechanism of signal adaptation and the presumed role of G-proteins.

Cyclic nucleotides, calcium, bicarbonate, and protein secretion in canine pancreatic juice in response to cholecystokinin–pancreozymin

1979 ◽  
Vol 57 (6) ◽  
pp. 541-546 ◽  
Author(s):  
H. L. Cailla ◽  
H. Sarles ◽  
M. V. Singer
Keyword(s):  
Cyclic Amp ◽  
Pancreatic Juice ◽  
Cyclic Gmp ◽  
Cyclic Nucleotides ◽  
Parallel Increase ◽  
Calcium Bicarbonate ◽  
Strong Linear Correlation ◽  
Protein Output ◽  
Dose Dependent ◽  
Stimulation Of

The secretion of cyclic AMP, cyclic GMP, protein, calcium, and bicarbonate in the pancreatic juice of three nonanesthetized dogs with chronic gastric and duodenal Thomas cannulae has been studied. Intravenous infusions of increasing doses of cholecystokinin–pancreozymin (CCK) (1.5, 3, 6, 12, 24 Crick Harper-Raper (CHR) U kg−1 h−1) were administered together with a continuous submaximal dose of secretin (1 clinical unit (CU) kg−1 h−1). Doubling CCK doses every 45 min induced a parallel increase in the output of both cyclic nucleotides. Cyclic AMP output peaked at between 15 and 30 min for 3 and 6 U kg−1 h−1 of CCK and later for 12 and 24 U kg−1 h−1 of CCK whereas cyclic GMP output increased more constantly. Calcium output followed a pattern similar to that of cyclic GMP secretion. Flow rate and protein output attained their peaks at between 30 and 45 min. A strong linear correlation was found between the quantities of cyclic AMP, cyclic GMP, and the quantities of protein secreted in response to each CCK dose. This study demonstrates the presence of cyclic GMP in the canine pancreatic juice and the dose-dependent stimulation of the secretion of cyclic GMP and cyclic AMP by CCK in the presence of secretin.

Possible role of cyclic GMP in stimulus-secretion coupling by salt gland of the duck

1979 ◽  
Vol 237 (5) ◽  
pp. C200-C204 ◽  
Author(s):  
D. J. Stewart ◽  
J. Sax ◽  
R. Funk ◽  
A. K. Sen
Keyword(s):  
Cyclic Amp ◽  
Guanylate Cyclase ◽  
Cyclic Gmp ◽  
Salt Gland ◽  
Domestic Ducks ◽  
Stimulus Secretion Coupling ◽  
Stimulation Of

Stimulation of salt galnd secretion in domestic ducks in vivo increased the cyclic GMP concentration of the tissue, but had no effect on cyclic AMP levels. Methacholine, which is known to stimulate sodium transport by the glands both in vivo and in vitro, stimulated ouabain-sensitive respiration in salt gland slices. Cyclic GMP stimulated ouabain-sensitive respiration to the same extent as methacholine. Guanylate cyclase stimulators, hydroxylamine and sodium azide, also stimulated ouabain-sensitive respiration. The stimulation of ouabain-sensitive respiration by methacholine was blocked either by atropine or by removal of calcium from the incubation medium. The stimulation of ouabain-sensitive respiration by cyclic GMP still occurred in the absence of calcium. The above observations seem to indicate that cyclic GMP acts as a tertiary link in the process of stimulus-secretion coupling in the tissue.

scholarly journals A pertussis-toxin-sensitive protein controls exocytosis in chromaffin cells at a step distal to the generation of second messengers

1991 ◽  
Vol 274 (2) ◽  
pp. 339-347 ◽  
Author(s):  
J M Sontag ◽  
D Thierse ◽  
B Rouot ◽  
D Aunis ◽  
M F Bader
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
G Protein ◽  
Pertussis Toxin ◽  
Chromaffin Cells ◽  
Second Messengers ◽  
Catecholamine Release ◽  
Secretory Process ◽  
Permeabilized Cells ◽  
Arachidonic Acid Concentration

The role of GTP-binding proteins (G-proteins) in the secretory process in chromaffin cells was investigated by studying the effects of pertussis toxin (PTX) on catecholamine release and generation of various second messengers. PTX was found to stimulate the catecholamine secretion induced by nicotine, 59 mM-K+ or veratridine. PTX also potentiated Ca2(+)-evoked catecholamine release from permeabilized chromaffin cells, suggesting that PTX substrate(s) regulate the exocytotic machinery at a step distal to the rise in intracellular Ca2+. We have investigated the possible intracellular pathways involved in the stimulation of secretion by PTX. PTX did not modify the translocation of protein kinase C (PKC) to membranes in intact or permeabilized cells; in addition, neither inhibitors nor activators of PKC had any effect on catecholamine release induced by PTX. Thus it seems unlikely that the effect of PTX on secretion is mediated by activation of PKC. The effect of PTX is also cyclic AMP-independent, as PTX did not change cytoplasmic cyclic AMP levels. The relationship between PTX treatment and arachidonic acid release was also examined. We found that an increase in cytoplasmic arachidonic acid concentration enhanced Ca2(+)-evoked catecholamine release in permeabilized cells, but arachidonic acid did not mimic the effect of PTX on the Ca2(+)-dose-response curve for secretion. Furthermore, PTX did not significantly modify the release of arachidonic acid measured in resting or stimulated chromaffin cells, suggesting that the stimulatory effect of PTX on secretion is not mediated by an activation of phospholipase A2. Taken together, these results suggest that PTX may modulate the intracellular machinery of secretion at a step distal to the generation of second messengers. In alpha-toxin-permeabilized cells, full retention of the PTX-induced activation of secretion was observed even 30 min after permeabilization. In contrast, when chromaffin cells were permeabilized with streptolysin-O (SLO), there was a marked progressive loss of the PTX effect. We found that SLO caused the rapid leakage of three G-protein alpha-subunits which are specifically ADP-ribosylated by PTX. We propose that a PTX-sensitive G-protein may play an inhibitory role in the final stages of the Ca2(+)-evoked secretory process in chromaffin cells.

Cyclic AMP and cyclic GMP independent stimulation of ventricular calcium current by peroxynitrite donors in guinea pig myocytes

2003 ◽  
Vol 197 (2) ◽  
pp. 284-296 ◽  
Author(s):  
Daniela Malan ◽  
Renzo Cesare Levi ◽  
Giuseppe Alloatti ◽  
Andrea Marcantoni ◽  
Ivano Bedendi ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Guinea Pig ◽  
Cyclic Gmp ◽  
Calcium Current ◽  
Stimulation Of
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