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Potentiation and inhibition of Ca 2+ release‐activated Ca 2+ channels by 2‐aminoethyldiphenyl borate (2‐APB) occurs independently of IP 3 receptors
Author(s) -
Prakriya Murali,
Lewis Richard S.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.t01-1-00003.x
Subject(s) - chemistry , extracellular , biophysics , intracellular , cytosol , long term potentiation , patch clamp , receptor , microbiology and biotechnology , biochemistry , biology , enzyme
1 The effects of the IP 3 ‐receptor antagonist 2‐aminoethyldiphenyl borate (2‐APB) on the Ca 2+ release‐activated Ca 2+ current ( I CRAC ) in Jurkat human T cells, DT40 chicken B cells and rat basophilic leukaemia (RBL) cells were examined. 2 2‐APB elicited both stimulatory and inhibitory effects on Ca 2+ influx through CRAC channels. At concentrations of 1–5 μ m , 2‐APB enhanced Ca 2+ entry in intact cells and increased I CRAC amplitude by up to fivefold. At levels ≥ 10 μ m , 2‐APB caused a transient enhancement of I CRAC followed by inhibition. 3 2‐APB altered the kinetics of fast Ca 2+ ‐dependent inactivation of I CRAC . At concentrations of 1–5 μ m , 2‐APB increased the rate of fast inactivation. In contrast, 2‐APB at higher concentrations (≥ 10 μ m ) reduced or completely blocked inactivation. 4 2‐APB inhibited Ca 2+ efflux from mitochondria. 5 2‐APB inhibited I CRAC more potently when applied extracellularly than intracellularly. Furthermore, increased protonation of 2‐APB at low pH did not affect potentiation or inhibition. Thus, 2‐APB may have an extracellular site of action. 6 Neither I CRAC activation by passive store depletion nor the effects of 2‐APB were altered by intracellular dialysis with 500 μg ml −1 heparin. 7ICRACis present in wild‐type as well as mutant DT40 B cells lacking all three IP 3 receptor isoforms. 2‐APB also potentiates and inhibits I CRAC in both cell types, indicating that 2‐APB exerts its effects independently of IP 3 receptors. 8 Our results show that CRAC channel activation does not require physical interaction with IP 3 receptors as proposed in the conformational coupling model. Potentiation of I CRAC by 2‐APB may be a useful diagnostic feature for positive identification of putative CRAC channel genes, and provides a novel tool for exploring the physiological functions of store‐operated channels.