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Fast Ca 2+ ‐dependent inactivation of the store‐operated Ca 2+ current ( I SOC ) in liver cells: a role for calmodulin
Author(s) -
Litjens Tom,
Harland M. Lyn,
Roberts Michael L.,
Barritt Gregory J.,
Rychkov Grigori Y.
Publication year - 2004
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 - 10.1113/jphysiol.2004.065870
Subject(s) - calmodulin , divalent , egta , chemistry , biophysics , bapta , membrane potential , calcium , extracellular , biochemistry , enzyme , biology , organic chemistry
Store‐operated Ca 2+ channels (SOCs) provide a major pathway for Ca 2+ entry in non‐excitable cells. SOCs in immortalized liver cells are highly selective for Ca 2+ over other cations and are similar to well‐studied Ca 2+ release activated Ca 2+ (CRAC) channels in haematopoietic cell lines. In the present work, employing H4IIE liver cells, we investigated fast inactivation of SOC current ( I SOC ), which occurs at membrane potentials below −60 mV. This inactivation was significantly reduced when BAPTA, a faster Ca 2+ buffer, was used instead of EGTA, and was completely abolished if Na + was used as a charge carrier in the absence of divalent cations in the external medium. These results suggested that fast inactivation of SOCs in H4IIE cells was Ca 2+ dependent and was similar to the fast inactivation of CRAC channels. Experiments showing that the fast inactivation of I SOC was not affected by the disruption of actin by latrunculin B indicate that the cytoskeleton is unlikely to be involved. To elucidate the mechanism of Ca 2+ dependence, a possible role of calmodulin (CaM) in SOCs' fast inactivation was investigated. The CaM inhibitors Mas‐7 and calmidazolium failed to affect I SOC fast inactivation, whereas over‐expression of a CaM inhibitor peptide or a mutant CaM lacking functional EF hands significantly altered the inactivation of I SOC . Out of two exponential components normally required to approximate kinetics of I SOC fast inactivation, the faster component was reduced in amplitude by 30%, compared to the control. The results presented suggest that CaM is responsible for at least part of Ca 2+ ‐dependent fast inactivation of I SOC in liver cells. It is hypothesized that CaM is tethered to the channel itself and therefore protected from chemical inhibitors.