Dicty News
Electronic Edition
Volume 22, number 13
May 28, 2004

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http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.

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  Abstracts
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A link of Ca2+ to cAMP oscillations in Dictyostelium: the calmodulin
antagonist W-7 potentiates cAMP relay and transiently inhibits the acidic
Ca2+-store

Dieter Malchow, Daniel F. Lusche and Christina Schlatterer 
Department of Biology, University of Konstanz, D-78457 Konstanz, Germany

BMC Developmental Biology, in press


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. 
Conclusion: 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. 


Submitted by: Christina Schlatterer [Christina.Schlatterer@uni-konstanz.de]


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[End Dicty News, volume 22, number 13]