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Intracellular ionic activities and transmembrane electrochemical potential differences in gallbladder epithelium.
The Journal of Membrane Biology
|September 14, 1979
Summary
This study measured intracellular ion activities in Necturus gallbladder epithelium, revealing active transport of potassium (K) and chloride (Cl) into cells and sodium (Na) out. This explains how the epithelium transports salt (NaCl).
Area of Science:
- Cellular Physiology
- Epithelial Transport
- Ion Homeostasis
Background:
- Necturus gallbladder epithelium actively transports NaCl from mucosa to serosa.
- Understanding intracellular ion activities is crucial for elucidating transport mechanisms.
Purpose of the Study:
- To measure intracellular ion activities (K, Cl, Na) in Necturus gallbladder epithelium.
- To determine the mechanisms of NaCl transport across the apical and basolateral membranes.
Main Methods:
- Utilized liquid ion-exchanger microelectrodes for precise intracellular ion activity measurements.
- Measured mean intracellular activities for potassium (K), chloride (Cl), and sodium (Na).
Main Results:
- Mean intracellular activities: K=87 mM, Cl=35 mM, Na=22 mM.
- Intracellular K and Cl activities exceed equilibrium values, indicating uphill transport.
- Intracellular Na activity is below equilibrium, suggesting active extrusion against its gradient.
Conclusions:
- NaCl entry at the apical membrane is likely driven by neutral transport coupled to the Na electrochemical potential.
- Active Na transport occurs at the basolateral membrane.
- Cl transport across the basolateral membrane involves coupled processes, not solely diffusion, potentially including a neutral NaCl pump, KCl transport, or Cl-anion exchange.