We have investigated Ca2+ release and receptor- and store-operated Ca2+ inf
luxes 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 in
flux were induced by thapsigargin and stimulation of G protein-coupled rece
ptors. The alleged noncompetitive IF, receptor inhibitor, 2-aminoethoxydiph
enyl berate (2-APE) rapidly blocked a major part of the secondary influx re
sponse 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 c
oncentration of 2-APE. In RBL-I cells, I-CRAC activity was rapidly blocked
by extracellular 2-APE whereas intracellular 2-APE was less effective. Stor
e-operated Ca2+ influxes were only partially blocked by 2-APB. in SH-SY5Y c
ells, 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 resist
ant to 2-APE, The results suggest, that 2-APB (1) may inhibit distinct subt
ypes of IP3 receptors with different sensitivity, and (2) that independentl
y of this, it also inhibits some store-operated Ca2+ channels via a direct,
extracellular action. (C) 2001 Harcourt Publishers Ltd.