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This Article Full Text Full Text (PDF) Supplemental data All Versions of this Article: 582/3/977    most recent jphysiol.2007.128413v1 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 Nam, J. H. Articles by Kim, S. J. Search for Related Content PubMed PubMed Citation Articles by Nam, J. H. Articles by Kim, S. J. Related Collections Review articles

¹ Department of Physiology, Seoul National University College of Medicine, Seoul 110-799, Republic of Korea
² Department of Physiology
³ Urology, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea

In various types of cells mechanical stimulation of the plasma membrane activates phospholipase C (PLC). However, the regulation of ion channels via mechanosensitive degradation of phosphatidylinositol 4,5-bisphosphate (PIP₂) is not known yet. The mouse B cells express large conductance background K⁺ channels (LK_bg) that are inhibited by PIP₂. In inside-out patch clamp studies, the application of MgATP (1 mM) also inhibited LK_bg due to the generation of PIP₂ by phosphoinositide (PI)-kinases. In the presence of MgATP, membrane stretch induced by negative pipette pressure activated LK_bg, which was antagonized by PIP₂ (> 1 µM) or higher concentration of MgATP (5 mM). The inhibition by PIP₂ was partially reversible. However, the application of methyl--cyclodextrin, a cholesterol scavenger disrupting lipid rafts, induced the full recovery of LK_bg activity and facilitated the activation by stretch. In cell-attached patches, LK_bg were activated by hypotonic swelling of B cells as well as by negative pressure. The mechano-activation of LK_bg was blocked by U73122, a PLC inhibitor. Neither actin depolymerization nor the inhibition of lipid phosphatase blocked the mechanical effects. Direct stimulation of PLC by m-3M3FBS or by cross-linking IgM-type B cell receptors activated LK_bg. Western blot analysis and confocal microscopy showed that the hypotonic swelling of WEHI-231 induces tyrosine phosphorylation of PLC2 and PIP₂ hydrolysis of plasma membrane. The time dependence of PIP₂ hydrolysis and LK_bg activation were similar. The presence of LK_bg and their stretch sensitivity were also proven in fresh isolated mice splenic B cells. From the above results, we propose a novel mechanism of stretch-dependent ion channel activation, namely, that the degradation of PIP₂ caused by stretch-activated PLC releases LK_bg from the tonic inhibition by PIP₂.

(Received 16 January 2007; accepted after revision 5 March 2007; first published online 8 March 2007)
Corresponding author S. J. Kim: Department of Physiology, Seoul National University College of Medicine, Seoul 110-799, Republic of Korea. Email: sjoonkim{at}snu.ac.kr

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