环磷酸腺苷（cAMP）通过激活血管纹边缘细胞顶端的IsK/KvLQT1通道增加钾离子分泌。

cAMP increases K+ secretion via activation of apical IsK/KvLQT1 channels in strial marginal cells.

作者信息

Sunose H, Liu J, Marcus D C

机构信息

Biophysics Laboratory, Boys Town National Research Hospital, Omaha, NE 68131, USA.

出版信息

Hear Res. 1997 Dec;114(1-2):107-16. doi: 10.1016/s0378-5955(97)00152-4.

DOI:10.1016/s0378-5955(97)00152-4

PMID:9447925

Abstract

In the cochlea, K+ is secreted by electrodiffusion across the apical membrane of strial marginal cells via the IsK/KvLQT1 ('IsK') channel. This channel complex has been reported to be activated in other systems by adenosine 3',5'-cyclic monophosphate (cAMP). Since several reports had suggested that cAMP is a second messenger in the cochlea, the effect of the cAMP pathway on transepithelial K+ secretion by strial marginal cells of the gerbil was studied. Both the transepithelial current (Isc) and K+ flux (JK) across strial marginal cell epithelium were measured; Isc in a micro-Ussing chamber and JK as the gradient of K+ concentration near the apical membrane. The apical membrane current (IIsK) and conductance (gIsK) of IsK channels were recorded with the on-cell macro-patch and the nystatin-perforated whole-cell patch clamp techniques. It has previously been shown that the apical IsK channel constitutes the primary pathway for K+ secretion. Cytoplasmic cAMP was elevated by applying dibutyryl cyclic-AMP (dbcAMP) or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) at 37 degrees C. dbcAMP (1 mM) increased Isc by 51 +/- 4% and IIsK in on-cell and whole-cell recordings increased by 214 +/- 63% and 390 +/- 61% above the control value, respectively. IBMX (1 mM) caused transient increases of Isc by 53 +/- 3% and IIsK in on-cell recordings by 177 +/- 75% above the control value. The leak conductance due to all non-IsK channel sources did not change in the presence of dbcAMP or IBMX. dbcAMP (1 mM at 24 degrees C) increased JK by 53 +/- 16% and Isc by 18 +/- 4%. IBMX (1 mM at 24 degrees C) had no effect, suggesting reduced activity of adenylate cyclase at this temperature. Our results demonstrate that the cAMP pathway is constitutively active in strial marginal cells and that the cAMP pathway stimulates transepithelial K+ secretion by increasing IsK channel current rather than by altering another transport pathway.

摘要

在耳蜗中，钾离子（K⁺）通过IsK/KvLQT1（“IsK”）通道经电扩散作用穿过血管纹边缘细胞的顶端膜而分泌。据报道，该通道复合体在其他系统中可被3',5'-环磷酸腺苷（cAMP）激活。由于有几份报告表明cAMP是耳蜗中的第二信使，因此研究了cAMP信号通路对沙鼠血管纹边缘细胞跨上皮K⁺分泌的影响。测量了跨血管纹边缘细胞上皮的跨上皮电流（Isc）和K⁺通量（JK）；在微尤斯灌流小室中测量Isc，将JK作为顶端膜附近K⁺浓度的梯度。使用细胞贴附式大膜片钳和制霉菌素穿孔全细胞膜片钳技术记录IsK通道的顶端膜电流（IIsK）和电导（gIsK）。先前已表明顶端IsK通道是K⁺分泌的主要途径。在37℃下，通过应用二丁酰环磷腺苷（dbcAMP）或磷酸二酯酶抑制剂3-异丁基-1-甲基黄嘌呤（IBMX）来升高细胞质中的cAMP。dbcAMP（1 mM）使Isc增加了51±4%，在细胞贴附式记录和全细胞记录中，IIsK分别比对照值增加了214±63%和390±61%。IBMX（1 mM）使Isc短暂增加了53±3%，在细胞贴附式记录中，IIsK比对照值增加了177±75%。在存在dbcAMP或IBMX的情况下，所有非IsK通道来源的漏电导均未改变。dbcAMP（24℃下1 mM）使JK增加了53±16%，使Isc增加了18±4%。IBMX（24℃下1 mM）没有作用，表明在此温度下腺苷酸环化酶的活性降低。我们的结果表明，cAMP信号通路在血管纹边缘细胞中持续活跃，并且cAMP信号通路通过增加IsK通道电流而非改变其他转运途径来刺激跨上皮K⁺分泌。