2-aminoethoxydiphenyl borate reveals heterogeneity in receptor activated Ca2+ discharge and store-operated Ca2+ influx

We have investigated Ca2+ release and receptor- and store-operated Ca2+ influxes in Chinese hamster ovary-K1 (CHO) cells, SH-SY5Y human neuroblastoma cells and RBL-1 rat basophilic leukemia cells using Fura-2 and patch-clamp measurements, Ca2+ release and subsequent Ni2+-sensitive, store-operated influx were induced by thapsigargin and stimulation of G protein-coupled receptors. The alleged noncompetitive IF, receptor inhibitor, 2-aminoethoxydiphenyl borate (2-APE) rapidly blocked a major part of the secondary influx response in CHO cells in a reversible manner. It also reduced Mn2+ influx in response to thapsigargin. Inhibition of Ca2+ release was also seen but this was less complete, slower in onset, less reversible, and required higher concentration of 2-APE. In RBL-I cells, I-CRAC activity was rapidly blocked by extracellular 2-APE whereas intracellular 2-APE was less effective. Store-operated Ca2+ influxes were only partially blocked by 2-APB. in SH-SY5Y cells, Ca2+ influxes were insensitive to 2-APE. Ca2+ release in RBL-1 cells was partially sensitive but in SH-SY5Y cells the release was totally resistant to 2-APE, The results suggest, that 2-APB (1) may inhibit distinct subtypes of IP3 receptors with different sensitivity, and (2) that independently of this, it also inhibits some store-operated Ca2+ channels via a direct, extracellular action. (C) 2001 Harcourt Publishers Ltd.