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Abstracts
REGULATION OF THE SODIUM PUMP IN INSULIN-SENSITIVE TISSUES Chibalin, A.V.
Integrative Physiology, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden
We have a longstanding interest in the regulation of skeletal muscle sodium pump activity and trafficking in response to metabolic challenges such as Type 2 diabetes, muscle contraction or physical activity/inactivity. Skeletal muscle Na,K-ATPase plays a central role in the clearance of K+ from the extracellular fluid, thus maintaining blood K+ concentration. We have shown that impaired skeletal muscle Na,K-ATPase activity in glucose intolerant animals is associated with changes in Na,K-ATPase subunits expression, plasma membrane abundance and altered expression and phosphorylation of the Na,K-ATPase-interacting protein phospholemman (PLM). Importantly, alterations in expression of sodium pump subunits and PLM precede development of insulin resistance. We hypothesize that disturbances in skeletal muscle Na,K-ATPase regulation may contribute to impaired ion homeo-stasis in insulin-resistant states such as obesity and Type 2 diabetes.
Contraction stimulates Na,K-ATPase activity in skeletal muscle partially via translocation of sodium pump
units to the plasma membrane. We have evidence that phosphorylation of PLM plays a critical role in the acute regulation of the Na,K-ATPase response to exercise/muscle contraction. Notably, spinal cord injury leads to rapid reduction of skeletal muscle Na,K-ATPase and PLM abundance in humans. Contraction and metabolic stress are potent activators of AMP-activated protein kinase (AMPK). AMPK activation stimulates Na,K-ATPase activity and increases the sodium pump cell surface abundance in skeletal muscle. AMPK stimulation leads to protein phosphatase 2Ac methylation and de-phosphorylation, which promotes activation of the phos-phatase and in turn cause de-phosphorylation of the Na,K-ATPase ai-subunit at Serl8 which may prevent sodium pump endocytosis. Thus, contrary to the common paradigm we demonstrate an AMPK-dependent activation of an energy consuming ion pumping process. Activation of AMPK may be a potential mechanism mediating exercise-and metabolic stress-induced activation of the sodium pump in skeletal muscle.
QUANTIFICATION OF CELL HYDRATION WITH FLUORESCENCE CORRELATION SPECTROSCOPY AND RAMAN SCANNING MICROSCOPY
Christmann, J.1, Azer, L.1, Dörr, D.2, Fuhr, G.2, Bastiaens, P.1, and Wehner, F.1
1 Max Planck Institute of Molecular Physiology, Dortmund, Germany
2 Fraunhofer Institute of Biomedical Engineering, St. Ingbert, Germany
Hydration plays a key role in cell physiology. We defined the hydration profiles of HeLa and HepG2 cells as a function of hypertonicity and temperature, at high time and spatial resolution using Fluorescence Correlation Spectroscopy (FCS) and Raman Scanning Microscopy (RSM) and the underlying activation energies were determined.
With FCS we quantified (l), the diffusion speed and the number of diffusing GFP particles in the cytoplasm and (2), the correlating changes in cell viscosity, under hypertonic conditions. Both parameters were correlated to
each other and exhibited a clear dependence on the osmolality.
RSM, on the other hand, allowed us to monitor directly the absolute amount of cell water and to map the hydration of a probe at high spatial resolution. This was instrumental in verifying the FCS measurements and, furthermore, the actual amount of bound water inside the cell could be computed, in a label-free fashion.
Our measurements prove the robustness of the cell volume regulatory machinery and define the energy profiles of its activation over a wide osmolality and temperature range.
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Бюллетень сибирской медицины, 2013, том 12, № 4, с. 24-68
