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Phenotype of a recombinant store‐operated channel: highly selective permeation of Ca 2+
Author(s) -
Warnat Jan,
Philipp Stephan,
Zimmer Stephanie,
Flockerzi Veit,
Cavalié Adolfo
Publication year - 1999
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.1469-7793.1999.0631p.x
Subject(s) - chinese hamster ovary cell , chemistry , biophysics , patch clamp , intracellular , biochemistry , biology , receptor
1 Genes related to trp (transient receptor potential ) are proposed to encode store‐operated channels. We examined the ionic permeation of recombinant channels formed by stable and transient expression of the TRP homologue bCCE1 in Chinese hamster ovary (CHO) cells (CHO(CCE1)) and rat basophilic leukaemia (RBL) cells, respectively. 2 Store‐operated currents were activated in CHO(CCE1) cells by internal dialysis of IP 3 under strong buffering of intracellular Ca 2+ . The action of IP 3 was mimicked by thapsigargin but not by IP 4 . 3 With extracellular Ca 2+ , Na + and Mg 2+ , the store‐operated currents of CHO(CCE1) rectified inwardly in the presence of internal Cs + . Outward currents were not detected below +80 mV. Identical currents were recorded with external Ba 2+ and also with no external Na + and Mg 2+ . In the absence of external Mg 2+ , the inward currents showed an anomalous mole fraction behaviour between Ca 2+ and Na + . Half‐maximal inhibition of Na + currents was observed with ≈100 nM and full block with 2‐5 μM external Ca 2+ . 4 In the parental CHO(‐) cells, IP 3 dialysis evoked inward currents that also displayed anomalous mole fraction behaviour between Ca 2+ and Na + . However, half‐maximal block of Na + currents required 5 times higher Ca 2+ concentrations in CHO(‐) cells. Additionally, the density of Ca 2+ and Na + currents at ‐80 mV was 5 and 2 times larger in CHO(CCE1) cells, respectively. 5 In RBL cells, dialysis of IP 3 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 in bCCE1‐transfected RBL cells probably reflects the phenotype of CCE1. These results suggest a highly selective permeation of Ca 2+ through recombinant channels formed by CCE1 either alone or in combination with endogenous channel proteins.