A link of Ca2+ to cAMP oscillations in Dictyostelium: the calmodulin antagonist W-7 potentiates cAMP relay and transiently inhibits the acidic Ca2+-store.
BACKGROUND
During early differentiation of Dictyostelium the attractant cAMP is released periodically to induce aggregation of the cells. Here we pursue the question whether pulsatile cAMP signaling is coupled to a basic Ca2+-oscillation.


RESULTS
We found that the calmodulin antagonist W-7 transiently enhanced cAMP spikes. We show that W-7 acts on an acidic Ca2+-store: it abolished ATP-dependent vesicular acidification, inhibited V-type H+ATPase activity more potently than the weaker antagonist W-5 and caused vesicular Ca2+-leakage. Concanamycin A, an inhibitor of the V-type H+-pump, blocked the Ca2+-leakage elicited by W-7 as well as cAMP-oscillations in the presence of W-7. Concanamycin A caused an increase of the cytosolic Ca2+-concentration whereas W-7 did not. In case of the latter, Ca2+ was secreted by the cells. In accord with our hypothesis that the link from Ca2+ to cAMP synthesis is mediated by a Ca2+-dependent phospholipase C we found that W-7 was not active in the phospholipase C knockout mutant.


CONCLUSIONS
We conclude that the potentiation of cAMP relay by W-7 is due to a transient inhibition of the acidic Ca2+-store. The inhibition of the proton pump by W-7 causes a leakage of Ca2+ that indirectly stimulates adenylyl cyclase activity via phospholipase C.
Malchow
Dieter
D
Department of Biology, University of Konstanz, D-78457 Konstanz, Germany. Renate.Gimmi@uni-konstanz.de
Lusche
Daniel F
DF
Schlatterer
Christina
C
D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000378:metabolism* / Q000502:physiology; D004023:Dictyostelium / Q000737:chemistry* / Q000166:cytology / Q000201:enzymology; D018942:Macrolides / Q000494:pharmacology; D015800:Protozoan Proteins / Q000502:physiology; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology
D018942:Macrolides; D015800:Protozoan Proteins; D013449:Sulfonamides; C017967:W 7; C036978:concanamycin A; D000242:Cyclic AMP; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010738:Type C Phospholipases; D002118:Calcium