2-aminoethoxydiphenyl borate reveals heterogeneity in receptor-activated Ca(2+) discharge and store-operated Ca(2+) influx.
We have investigated Ca(2+) release and receptor- and store-operated Ca(2+) 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. Ca(2+) release and subsequent Ni(2+)-sensitive, store-operated influx were induced by thapsigargin and stimulation of G protein-coupled receptors. The alleged noncompetitive IP3 receptor inhibitor,2-aminoethoxydiphenyl borate (2-APB) rapidly blocked a major part of the secondary influx response in CHO cells in a reversible manner. It also reduced Mn(2+) influx in response to thapsigargin. Inhibition of Ca(2+) release was also seen but this was less complete, slower in onset, less reversible, and required higher concentration of 2-APB. In RBL-1 cells, I(CRAC) activity was rapidly blocked by extracellular 2-APB whereas intracellular 2-APB was less effective. Store-operated Ca(2+) influxes were only partially blocked by 2-APB. In SH-SY5Y cells, Ca(2+) influxes were insensitive to 2-APB. Ca(2+) release in RBL-1 cells was partially sensitive but in SH-SY5Y cells the release was totally resistant to 2-APB. 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 Ca(2+) channels via a direct, extracellular action.
Kukkonen
J P
JP
Department of Physiology, Division of Cell Physiology, Uppsala University, Uppsala, Sweden. jkukkone@fysiologi.uu.se
Lund
P E
PE
Akerman
K E
KE
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology*; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D002614:Chelating Agents / Q000494:pharmacology; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008345:Manganese / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D014407:Tumor Cells, Cultured
D001896:Boron Compounds; D015220:Calcium Channels; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D008345:Manganese; D019284:Thapsigargin; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium; D016257:Fura-2