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Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
The membrane-permeable, noncompetitive inositol 1,4,5-trisphosphate
(IP3)-receptor inhibitor 2-aminoethoxydiphenyl borane (2-APB) has
been widely used to probe for IP3-receptor involvement in calcium
signaling pathways. However, a number of recent studies in different cell
types revealed other sites of action of 2-APB. In this study, we examined the
influence of 2-APB on capacitative calcium entry and intracellular
Ca2+ concentrations in rat basophilic leukemia (RBL-2H3
m1) cells. 2-APB was found to inhibit capacitative calcium entry, but at
concentrations greater than 50 µM, a new effect of 2-APB was observed. When
capacitative calcium entry was blocked with Gd3+, 2-APB
caused an increase in cytoplasmic Ca2+. This increase in
intracellular Ca2+ was not caused by altered buffering
of cytoplasmic Ca2+ and was not caused by or in any way
affected by the depletion of intracellular Ca2+ stores.
Associated with the increase in intracellular Ca2+, in
the presence of 2 mM Ca2+, 2-APB activated single
channels in the plasma membrane with a conductance of
50 pS. These
channels seem to be nonselective cation channels; monovalent cations are the
major carriers of current, but finite permeability to
Ca2+ leads to a significant intracellular
Ca2+ signal. Experiments with excised patches indicate
that 2-APB activates these channels from the outer aspect of the cell
membrane. This effect of 2-APB further illustrates the complex actions of this
compound and reveals the presence in RBL-2H3 m1 cells of a novel, ligand-gated
calcium-permeable channel.
Address correspondence to: Dr. James W. Putney, Jr., National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709. E-mail: putney{at}niehs.nih.gov
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