Phenotype of a recombinant store-operated channel: highly selective permeation of Ca2+

1. Genes related to trp (transient receptor potential) are proposed to enco de store-operated channels. We examined the ionic permeation of recombinant channels formed by stable and transient expression of the TRP homologue bC CE1 in Chinese hamster ovary (CHO) cells (CHO(CCE1)) and rat basophilic leu kaemia (RBL) cells, respectively. 2. Store-operated currents were activated in CHO(CCE1) cells by internal di alysis of IF, under strong buffering of intracellular Ca2+. The action of I P3 was mimicked by thapsigargin but not by IP4. 4. With extracellular Ca2+, Na+ and Mg2+, the store-operated currents of CH O(CCE1) rectified inwardly in the presence of internal Cs+. Outward current s were not detected below +80 mV. Identical currents were recorded with ext ernal Ba2+ and also with no external Na+ and Mg2+ In the absence of externa l Mg2+, the inward currents showed an anomalous mole fraction behaviour bet ween Ca2+ and Na+. Half-maximal inhibition of Na+ currents was observed wit h similar to 100 nM and full block with 2-5 mu M external Ca24. In the parental CHO(-) cells, IP3 dialysis evoked inward currents that a lso displayed anomalous mole fraction behaviour between Ca2+ and Na+. Howev er, half-maximal block of Na+ currents required 5 times higher Ca2+ concent rations in CHO(-) cells. Additionally, the density of Ca2+ and Na+ currents at -80 mV was 5 and 2 times larger in CHO(CCE1) cells, respectively. 5. In RBL cells, dialysis of IP3 evoked store-operated currents that showed 1.4-fold larger densities at -80 mV in cells expressing bCCE1. 6. The enhanced density of store-operated currents in CHO(CCE1) cells and i n bCCE1-transfected RBL cells probably reflects the phenotype of CCE1. Thes e results suggest a highly selective permeation of Ca2+ through recombinant channels formed by CCE1. either alone or in combination with endogenous ch annel proteins.