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Insulin and isoproterenol differentially regulate mitogen-activated protein kinase-dependent Na(+)-K(+)-2Cl(-)
Aidar R Gosmanov1, Donald B Thomason
1Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
Abstract:
Recent studies have demonstrated that p44/42(MAPK) extracellular signal-regulated kinase (ERK)1 and -2-dependent Na(+)-K(+)-2Cl(-) co-transporter (NKCC) activity may contribute to total potassium uptake by skeletal muscle. To study the precise mechanisms regulating NKCC activity, rat soleus and plantaris muscles were stimulated ex vivo by insulin or isoproterenol (ISO). Both hormones stimulated total uptake of the potassium congener (86)Rb by 25--70%. However, only ISO stimulated the NKCC-mediated (86)Rb uptake. Insulin inhibited the ISO-stimulated NKCC activity, and this counteraction was sensitive to the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 in the predominantly slow-twitch soleus muscle. Pretreatment of the soleus muscle with the phosphatidylinositol (PI) 3-kinase inhibitors wortmannin and LY294002 or with SB203580 uncovered an insulin-stimulated NKCC activity and also increased the insulin-stimulated phosphorylation of ERK. In the predominantly fast-twitch plantaris muscle, insulin-stimulated NKCC activity became apparent only after inhibition of PI 3-kinase activity, accompanied by an increase in ERK phosphorylation. PI 3-kinase inhibitors also abolished insulin-stimulated p38 MAPK phosphorylation in the plantaris muscle and Akt phosphorylation in both muscles. These data demonstrated that insulin inhibits NKCC-mediated transport in skeletal muscle through PI 3-kinase-sensitive and SB203580-sensitive mechanisms. Furthermore, differential activation of signaling cascade elements after hormonal stimulation may contribute to fiber-type specificity in the control of potassium transport by skeletal muscle.
Insights
Insulin inhibits potassium transport via the Na(+)-K(+)-2Cl(-) co-transporter (NKCC) in skeletal muscle through PI 3-kinase and p38 MAPK pathways. This regulation shows fiber-type specificity, impacting total potassium uptake.
Area of Science:
- Physiology
- Molecular Biology
- Cell Signaling
Background:
- Extracellular signal-regulated kinase (ERK) pathways regulate Na(+)-K(+)-2Cl(-) co-transporter (NKCC) activity, influencing potassium uptake in skeletal muscle.
- Understanding the precise signaling mechanisms controlling NKCC activity is crucial for comprehending potassium homeostasis in muscle tissue.
Purpose of the Study:
- To elucidate the specific molecular mechanisms by which insulin and isoproterenol regulate NKCC activity in rat soleus and plantaris muscles.
- To investigate the roles of phosphatidylinositol 3-kinase (PI 3-kinase) and p38 mitogen-activated protein kinase (MAPK) in mediating insulin's effects on NKCC activity and potassium transport.
Main Methods:
- Ex vivo stimulation of rat soleus and plantaris muscles with insulin or isoproterenol (ISO).
- Measurement of total and NKCC-mediated potassium congener (86)Rb uptake.
- Pharmacological inhibition of PI 3-kinase (wortmannin, LY294002) and p38 MAPK (SB203580).
- Assessment of ERK, p38 MAPK, and Akt phosphorylation levels.
Main Results:
- Both insulin and ISO increased total (86)Rb uptake, but only ISO stimulated NKCC-mediated uptake.
- Insulin inhibited ISO-stimulated NKCC activity, an effect sensitive to SB203580 in soleus muscle.
- Inhibition of PI 3-kinase uncovered insulin-stimulated NKCC activity and increased ERK phosphorylation in both soleus and plantaris muscles.
- Insulin-stimulated p38 MAPK and Akt phosphorylation were abolished by PI 3-kinase inhibitors.
Conclusions:
- Insulin inhibits NKCC-mediated potassium transport in skeletal muscle via PI 3-kinase-dependent and SB203580-sensitive pathways.
- Differential activation of signaling cascades, including ERK and p38 MAPK, contributes to fiber-type-specific regulation of potassium transport by insulin.