Submitted on June 13, 2003
Accepted on October 22, 2003
ATP-sensitive Potassium Channels Mediate Hyperosmotic Stimulation of NKCC in Slow-twitch Muscle
Aidar R Gosmanov1, Zheng Fan1, Xianqiang Mi1, Edward G Schneider1, and Donald B Thomason1*
1 Physiology, The University of Tennessee Health Science Center, Memphis, TN, USA
* To whom correspondence should be addressed. E-mail: thomason{at}physio1.utmem.edu.
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 PKA stimulators isoproterenol and forskolin. Furthermore, pinacidil (a KATP channel opener) or inhibition of glycolysis increased NKCC activity in the soleus muscle, but not 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 did not affect hyperosmolarity-induced 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.
