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Ca 2+ store dynamics determines the pattern of activation of the store‐operated Ca 2+ current I CRAC in response to Ins P 3 in rat basophilic leukaemia cells
Author(s) -
Glitsch Maike D.,
Parekh Anant B.
Publication year - 2000
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.1469-7793.2000.t01-2-00283.x
Subject(s) - chemistry , intracellular , biophysics , inositol , phosphatase , analytical chemistry (journal) , receptor , biochemistry , phosphorylation , biology , chromatography
1 I CRAC and intracellular inositol 1,4,5‐trisphosphate (Ins P 3 ) concentration is complex. In rat basophilic leukaemia (RBL‐1) cells dialysed with high intracellular Ca 2+ buffer, the relationship is supra‐linear with a Hill coefficient of 12 and resembles an apparent ‘all‐or‐none’ phenomenon. The non‐linearity seems to arise from Ins P 3 metabolism. However, it is not clear which Ins P 3 ‐metabolising pathway engenders the non‐linear behaviour nor whether I CRAC is always activated to its maximal extent by Ins P 3 . 2 Using the whole‐cell patch clamp technique, we dialysed RBL‐1 cells with different concentrations of the Ins P 3 analogue Ins P 3 ‐F. Ins P 3 ‐F is broken down by Ins(1,4,5) P 3 5‐phosphatase but is not a substrate for Ins(1,4,5) P 3 3‐kinase. The relationship between Ins P 3 ‐F and I CRAC amplitude was supra‐linear and very similar to that with Ins P 3 but was distinct from the graded relationship seen with the non‐metabolisable analogue Ins2,4,5 P 3 . 3 In the presence of high intracellular Ca 2+ buffer, Ins P 3 ‐F activated I CRAC to its maximal extent. With moderate Ca 2+ buffer, however, sub‐maximal I CRAC could be obtained to a maximal Ins P 3 ‐F concentration. Nevertheless, the relationship between the amplitude of I CRAC and Ins P 3 ‐F concentration was still supra‐linear. 4 Submaximal I CRAC in response to Ins P 3 ‐F in the presence of moderate Ca 2+ buffer was due to partial depletion of the stores, because the size of the current could be increased by thapsigargin. 5 The data suggest that first, Ins(1,4,5) P 3 5‐phosphatase is an important factor which contributes to the non‐linear relationship between Ins P 3 concentration and the amplitude of I CRAC and second, Ins P 3 does not always activate I CRAC to its maximal extent. At moderate buffer strengths, submaximal I CRAC is evoked by maximal Ins P 3 . However, the supra‐linear relationship between Ins P 3 concentration and amplitude of the current still holds.