Adenophostin A can stimulate Ca2+ influx without depleting the inositol 1,4,5-trisphosphate-sensitive Ca2+ stores in the Xenopus oocyte.
Adenophostin A possesses the highest known affinity for the inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) receptor (InsP3R). The compound shares with Ins(1,4,5)P3 those structural elements essential for binding to the InsP3R. However, its adenosine 2'-phosphate moiety has no counterpart in the Ins(1,4,5)P3 molecule. To determine whether its unique structure conferred a distinctive biological activity, we characterized the adenophostin-induced Ca2+ signal in Xenopus oocytes using the Ca2+-gated Cl- current assay. In high concentrations, adenophostin A released Ca2+ from Ins(1,4, 5)P3-sensitive stores and stimulated a Cl- current that depended upon the presence of extracellular Ca2+. We used this Cl- current as a marker of Ca2+ influx. In low concentrations, however, adenophostin A stimulated Ca2+ influx exclusively. In contrast, Ins(1,4,5)P3 and (2-hydroxyethyl)-alpha-D-glucopyranoside 2',3, 4-trisphosphate, an adenophostin A mimic lacking most of the adenosine moiety, always released intracellular Ca2+ before causing Ca2+ influx. Ins(1,4,5)P3 could still release Ca2+ during adenophostin A-induced Ca2+ influx, confirming that the Ins(1,4, 5)P3-sensitive intracellular Ca2+ stores had not been emptied. Adenophostin- and Ins(1,4,5)P3-induced Ca2+ influx were not additive, suggesting that both agonists stimulated a common Ca2+ entry pathway. Heparin, which blocks binding to the InsP3R, prevented adenophostin-induced Ca2+ influx. These data indicate that adenophostin A can stimulate the influx of Ca2+ across the plasma membrane without inevitably emptying the Ins(1,4,5)P3-sensitive intracellular Ca2+ stores.
DeLisle
S
S
Veterans Administration Medical Center, Department of Internal Medicine, and Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City, Iowa 52240, USA. sdelisle@umabnet.ab.umd.edu
Marksberry
E W
EW
Bonnett
C
C
Jenkins
D J
DJ
Potter
B V
BV
Takahashi
M
M
Tanzawa
K
K
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D014981:Xenopus
C085029:adenophostin A; D008345:Manganese; D015544:Inositol 1,4,5-Trisphosphate; D000241:Adenosine; D002118:Calcium