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dictyNews Volume 24 Number 02
Dicty News
Electronic Edition
Volume 24, number 2
February 11, 2005
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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cGMP-phosphodiesterase antagonists inhibit Ca2+ -influx in Dictyostelium
discoideum and bovine cyclic-nucleotide-gated-channel
Daniel F.Lusche1, Hiroshi Kaneko2, and Dieter Malchow1
1 Department of Biology University of Konstanz
2 Department of Physiology University of Heidelberg
Eur. J. Pharmacol., in press
We used antagonists of cGMP-phosphodiesterases to examine the role of cGMP
for light-scattering oscillations and cAMP-induced Ca2+-influx in
Dictyostelium discoideum, however, SCH 51866 (cis-5,6a,7,8,9,9a-hexahydro-2-[4-(trifluoromethyl)phenylmethyl]-5-methyl-
cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one) and sildenafil citrate
(1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1-H-pyrazolo[4,3-d]pyrimidin-5-yl)
-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate) were poor inhibitors of
cGMP-hydrolysis. Instead, SCH 51866 (IC50=16 µM) and sildenafil, blocked
chemoattractant (cAMP) -induced Ca2+ -influx as determined with a
Ca2+-specific electrode. SCH 51866 (150 µM) affected neither spontaneous
cGMP transients during light-scattering-oscillations nor cAMP-mediated
K+-efflux. SCH 51866 and sildenafil are competitive inhibitors of cGMP
phosphodiesterases. However, the activity of cGMP-dependent protein kinase
Ia (PKGIa) was not altered by SCH 51866 (150 µM). By contrast, patch-clamp
measurements of bovine cone cGMP-gated channels
(cyclic-nucleotide-gated-channel, CNGA3), stably expressed in human embryonic
kidney cells, HEK 293 cells, revealed reversible, competitive and
dose-dependent inhibition of sodium currents by SCH 51866 (IC50=25 µM) and
sildenafil, but not by another inhibitor of cGMP-phosphodiesterases,
UK 114,542. The possibility that D. discoideum cells also express a
cGMP-regulated channel is supported by our finding that LY 83583
(6-(phenylamino)-5,8-quinolinedione) (35 µM), known to inhibit
cyclic-nucleotide-gated-channels as well as guanylyl-cyclases, reduced
cAMP-induced Ca2+-influx in D. discoideum, but did not affect cAMP-induced
cGMP accumulation. Utilizing a PdeD null strain that exhibits a prolonged
and elevated cGMP transient following receptor activation, we found that
the inhibition of Ca2+-influx by SCH 51866 in the wildtype was absent in
the mutant. Our results show that SCH 51866 and sildenafil are antagonists
of a Ca2+-permeable channel (CNGA3) and that both compete with cGMP for a
regulatory site of Ca2+-influx in D. discoideum.
Submitted by: Daniel Lusche [Daniel.Lusche@web.de]
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[End Dicty News, volume 24, number 2] 
