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This Article Full Text Full Text (PDF) All Versions of this Article: 558/1/85    most recent jphysiol.2004.065870v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Litjens, T. Articles by Rychkov, G. Y. Search for Related Content PubMed PubMed Citation Articles by Litjens, T. Articles by Rychkov, G. Y.

¹ School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia² Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia, Adelaide, South Australia 5001, Australia

Store-operated Ca²⁺ channels (SOCs) provide a major pathway for Ca²⁺ entry in non-excitable cells. SOCs in immortalized liver cells are highly selective for Ca²⁺ over other cations and are similar to well-studied Ca²⁺ release activated Ca²⁺ (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 Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ 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 Ca²⁺-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.

(Received 5 April 2004; accepted after revision 28 April 2004; first published online 30 April 2004)
Corresponding author G. Rychkov: School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, 5005, Australia. Email: grigori.rychkov{at}adelaide.edu.au

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