Gosmanov Aidar R, Fan Zheng, Mi Xianqiang, Schneider Edward G, Thomason Donald B
Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
Am J Physiol Cell Physiol. 2004 Mar;286(3):C586-95. doi: 10.1152/ajpcell.00247.2003. Epub 2003 Oct 30.
In mildly hyperosmotic medium, activation of the Na+ -K+ -2Cl- cotransporter (NKCC) counteracts skeletal muscle cell water loss, and compounds that stimulate protein kinase A (PKA) activity inhibit the activation of the NKCC. The aim of this study was to determine the mechanism for PKA inhibition of NKCC activity in resting skeletal muscle. Incubation of rat slow-twitch soleus and fast-twitch plantaris muscles in isosmotic medium with the PKA inhibitors H-89 and KT-5720 caused activation of the NKCC only in the soleus muscle. NKCC activation caused by PKA inhibition was insensitive to MEK MAPK inhibitors and to insulin but was abolished by the PKA stimulators isoproterenol and forskolin. Furthermore, pinacidil [an ATP-sensitive potassium (KATP) channel opener] or inhibition of glycolysis increased NKCC activity in the soleus muscle but not in the plantaris muscle. Preincubation of the soleus muscle with glibenclamide (a KATP channel inhibitor) prevented the NKCC activation by hyperosmolarity, PKA inhibition, pinacidil, and glycolysis inhibitors. In contrast, glibenclamide stimulated NKCC activity in the plantaris muscle. In cells stably transfected with the Kir6.2 subunit of the of KATP channel, inhibition of glycolysis activated potassium current and NKCC activity. We conclude that activation of KATP channels in slow-twitch muscle is necessary for activation of the NKCC and cell volume restoration in hyperosmotic conditions.
在轻度高渗介质中，钠钾氯协同转运体（NKCC）的激活可抵消骨骼肌细胞的水分流失，而刺激蛋白激酶A（PKA）活性的化合物会抑制NKCC的激活。本研究的目的是确定PKA抑制静息骨骼肌中NKCC活性的机制。将大鼠慢肌比目鱼肌和快肌趾长伸肌在等渗介质中与PKA抑制剂H-89和KT-5720一起孵育，结果仅比目鱼肌中的NKCC被激活。PKA抑制引起的NKCC激活对MEK MAPK抑制剂和胰岛素不敏感，但被PKA激动剂异丙肾上腺素和福斯可林消除。此外，吡那地尔[一种ATP敏感性钾（KATP）通道开放剂]或糖酵解抑制增加了比目鱼肌中的NKCC活性，但未增加趾长伸肌中的NKCC活性。用格列本脲（一种KATP通道抑制剂）预孵育比目鱼肌可防止高渗、PKA抑制、吡那地尔和糖酵解抑制剂引起的NKCC激活。相反，格列本脲刺激了趾长伸肌中的NKCC活性。在稳定转染KATP通道Kir6.2亚基的细胞中，糖酵解抑制激活了钾电流和NKCC活性。我们得出结论，慢肌中KATP通道的激活对于高渗条件下NKCC的激活和细胞体积恢复是必要的。
