Effects of anisosmotic medium on cell volume, transmembrane potential and intracellular K+ activity in mouse hepatocytes

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Abstract
Mouse hepatocytes in primary monolayer culture (4 hr) were exposed for 10 min at 37°C to anisosmotic medium of altered NaCl concentration. Hepatocytes maintained constant relative cell volume (experimental volume/control volume) as a function of external medium relative osmolality (control mOsm/experimental mOsm), ranging from 0.8 to 1.5. In contrast, the relative cell volume fit a predicted Boyle-Van't Hoff plot when the experiment was done at 4°C. Mouse liver slices were used for electrophysiologic studies, in which hepatocyte transmembrane potential (V m ) and intracellular K+ activity (a K i ) were recorded continuously by open-tip and liquid ion-exchanger ion-sensitive glass microelectrodes, respectively. Liver slices were superfused with control and then with anisosmotic medium of altered NaCl concentration.V m increased (hyperpolarized) with hypoosmotic medium and decreased (depolarized) with hyperosmotic medium, and ln [10(experimentalV m /controlV m )] was a linear function of relative osmolality (control mOsm/experimental mOsm) in the range 0.8–1.5. Thea K i did not change when medium osmolality was decreased 40–70 mOsm from control of 280 mOsm. Similar hypoosmotic stress in the presence of either 60mm K+ or 1mm quinine HCl or at 27°C resulted in no change inV m compared with a 20-mV increase inV m without the added agents or at 37°C. We conclude that mouse hepatocytes maintain their volume anda K i in response to anisosmotic medium; however,V m behaves as an osmometer under these conditions. Also, increases inV m by hypoosmotic stress were abolished by conditions or agents that inhibit K+ conductance.