Adenophostin A and inositol 1,4,5-trisphosphate differentially activate Cl- currents in Xenopus oocytes because of disparate Ca2+ release kinetics.
Depletion of endoplasmic reticulum Ca2+ stores induces Ca2+ entry from the extracellular space by a process termed "store-operated Ca2+ entry" (SOCE). It has been suggested that the novel fungal metabolite adenophostin-A may be able to stimulate Ca2+ entry without stimulating Ca2+ release from stores. To test this idea further, we compared Ca2+ release, SOCE, and the stimulation of Ca2+-activated Cl- currents in Xenopus oocytes in response to inositol 1,4,5-trisphosphate (IP3) and adenophostin-A injection. IP3 stimulated an outward Cl- current, ICl1-S, in response to Ca2+ release from stores followed by an inward current, ICl2, in response to SOCE. In contrast, low concentrations of adenophostins (AdAs) activated ICl2 without activating ICl1-S, consistent with the suggestion that AdA can activate Ca2+ entry without stimulating Ca2+ release. However, when Ca2+ entry has been stimulated by AdA, Ca2+ stores are largely depleted of Ca2+, as assessed by the inability of ionomycin to release additional Ca2+. The Ca2+ release stimulated by AdA, however, was 7 times slower than the release stimulated by IP3, which could explain the minimal activation of ICl1-S; when Ca2+ is released slowly, the threshold level required for ICl1-S activation is not attained.
Machaca
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K
Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Hartzell
H C
HC
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D065101:Chloride Channel Agonists; D017931:DNA Primers; D005260:Female; D005456:Fluorescent Dyes; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D018613:Microscopy, Confocal; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014982:Xenopus laevis