Functional hepatocyte cation compartmentation demonstrated with 133Cs NMR

Area of Science:

• Biophysics
• Cell Biology
• Biochemistry

Background:

• Intracellular cation distribution is crucial for cellular function.
• Nuclear magnetic resonance (NMR) spectroscopy offers a non-invasive method to study cation dynamics.
• Cesium-133 (133Cs), a potassium congener, has a wide chemical shift range suitable for NMR studies.

Purpose of the Study:

• To investigate intracellular cation distribution using 133Cs NMR.
• To identify distinct intracellular compartments within hepatocytes based on 133Cs chemical shifts.
• To explore the dynamic nature of these compartments under metabolic stress.

Main Methods:

• Utilized 133Cs NMR spectroscopy on isolated perfused rat hepatocytes.
• Administered cesium to rats to load hepatocytes with 133Cs.
• Induced metabolic changes using anoxia, aglycemia, and digitonin.

Main Results:

• Observed two distinct intracellular 133Cs NMR signals, indicating separate compartments with different chemical shifts (2.44 +/- 0.07 ppm and 1.21 +/- 0.18 ppm).
• The high-frequency signal represented 62 +/- 10% of total intracellular cesium.
• Metabolic manipulations altered the distribution of 133Cs between the compartments, demonstrating their dynamic nature.
• Metabolic changes suggested the high-frequency peak originates from the cytoplasm and the low-frequency peak from mitochondria.

Conclusions:

• 133Cs NMR effectively distinguishes at least two intracellular compartments in hepatocytes.
• These compartments exhibit slow exchange kinetics on the NMR timescale.
• The dynamic redistribution of cesium under metabolic stress provides insights into cellular compartment function, potentially implicating cytoplasm and mitochondria.