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J. Biol. Chem., Vol. 279, Issue 20, 20643-20654, May 14, 2004

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Membrane-delimited Regulation of Novel Background K⁺ Channels by MgATP in Murine Immature B Cells^*

Joo Hyun Nam, Ji-Eun Woo, Dae-Yong Uhm, and Sung Joon Kim

From the Department of Physiology, Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea

In WEHI-231, a representative immature B cell line, Ca²⁺ entry is paradoxically augmented by treatment with 2-aminoethoxydiphenyl borate (2-APB), a blocker of inositol 1,4,5-trisphosphate receptor and of nonselective cation channels (Nam, J. H., Yun, S. S., Kim, T. J., Uhm, D.-Y., and Kim, S. J. (2003) FEBS Lett. 535, 113–118). The initial goal of the present study was to elucidate the effects of 2-APB on membrane currents, which revealed the presence of novel K⁺ channels in WEHI-231 cells. Under whole-cell patch clamp conditions, 2-APB induced background K⁺ current (I_K,bg) and hyperpolarization in WEHI-231 cells. Lowering of intracellular MgATP also induced the I_K,bg. The I_K,bg was blocked by micromolar concentrations of quinidine but not by tetraethylammonium. In a single channel study, two types of voltage-independent K⁺ channels were found with large (346 picosiemens) and medium conductance (112 picosiemens), named BK_bg and MK_bg, respectively. The excision of membrane patches (inside-out (i-o) patches) greatly increased the P_o of BK_bg. In i-o patches, cytoplasmic MgATP (IC₅₀ = 0.18 mM) decreased the BK_bg activity, although non-hydrolyzable adenosine 5'-(,-imino)triphosphate had no effect. A pretreatment with Al³⁺ or wortmannin (50 µM) blocked the inhibitory effects of MgATP. A direct application of phosphoinositide 4,5-bisphosphate (10 µM) inhibited the BK_bg activity. Meanwhile, the activity of MK_bg was unaffected by MgATP. In cell-attached conditions, the BK_bg activity was largely increased by 2-APB. In i-o patches, however, the MgATP-induced inhibition of BK_bg was weakly reversed by the addition of 2-APB. In summary, WEHI-231 cells express the unique background K⁺ channels. The BK_bgs are inhibited by membrane-delimited elevation of phosphoinositide 4,5-bisphosphate. The activation of BK_bg would hyperpolarize the membrane, which augments the calcium influx in WEHI-231 cells.

Received for publication, November 17, 2003 , and in revised form, March 3, 2004.

^* This work was supported by Samsung Grants SBRI B-A2–302 (to D.-Y. U.) and B-A2–102 (to S. J. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Physiology, Sungkyunkwan University School of Medicine, Changan-Gu, Cheoncheon-Dong 300, Suwon 440-746, Korea. Tel.: 82-31-299-6104; Fax: 82-31-299-6129; E-mail: sjoonkim{at}med.skku.ac.kr.

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