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Currents in Xenopus laevis Oocytes
Department of Anatomy and Cell Biology, Emory University School of
Medicine, Atlanta, Georgia 30322-3030
Adenophostin-A, a novel compound isolated from cultures of
Penicillium brevicompactum, has been shown to stimulate
Ca2+ release from inositol-1,4,5-trisphosphate
(IP3)-sensitive Ca2+ stores in microsomal
preparations, permeabilized cells, and lipid vesicles containing
purified IP3 receptor. The purpose of the current study was
to compare the effects of adenophostin-A and IP3 on
Ca2+ release from stores and Ca2+ influx in
intact Xenopus laevis oocytes. Ca2+ influx
though store-operated Ca2+ channels and Ca2+
release from stores were monitored by measuring two Ca2+
-activated Cl
currents that can be used as real-time
indicators of Ca2+ release and Ca2+ influx
(ICl-1 and ICl-2, respectively). We find that
high concentrations (final intraoocyte concentrations of 5-10
µM) of adenophostin-A and IP3 stimulate a
large Ca2+ release from stores (as measured by
ICl-1) followed by Ca2+ influx (as measured by
ICl-2). Low concentrations (~50 nM) of IP3 stimulate oscillations in Ca2+ release
without stimulating Ca2+ influx. In contrast, low
concentrations of adenophostin-A can stimulate Ca2+ influx
without stimulating a large Ca2+ release. However,
Ca2+ influx did not occur in the complete absence of
Ca2+ release. Therefore, it is unlikely that adenophostin-A
directly stimulates store-operated Ca2+ channels. We
hypothesize that adenophostin-A releases Ca2+ from a
subpopulation of stores that is tightly coupled to store-operated Ca2+ channels.
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