Involvement of cell calcium and transmembrane potential in control of hepatocyte volume

This study examined the role of hepatocyte calcium and cytoskeleton in activation of hyposmotic stress-induced increases in hepatocyte transmembrane potential and control of cell volume. Hepatocyte transmembrane potential was measured by glass microelectrodes in mouse liver slices before and after exposure to hyposmotic medium. Hepatocytes were loaded with tetramethylammonium by briefly exposing liver slices to nystatin, a cation poreforming antibiotic. Changes in hepatocyte steady-state water volume were determined by changes in intracellular tetramethylammonium activity measured with tetramethylammonium-sensitive, double-barrel micro-electrodes 4 min after exposure to hyposmotic medium. Hyposmotic stress of 74% of the control osmolality (approximately 280 mOsm) hyperpolarized hepatocyte transmembrane potential by 1.83 times the control hepatocyte transmembrane potential, and cell water volume increased by a factor of 1.19. The Ca2+ channel blocker verapamil (100 mumol/L) completely inhibited hyposmotic stress-induced hyperpolarization of hepatocyte transmembrane potential. This inhibitory effect diminished at doses of 37.5 or 50 mumol/L, but even these hyperpolarizations were decreased significantly compared with control. Hyposmotic stress during added verapamil dosage (50 mumol/L) also resulted in 23% greater cell swelling compared with control. Ca(2+)-free medium plus ethylene glycol-bis (beta-aminoethylether)-N,N'-tetraacetic acid (5 mmol/L) inhibited hyposmotic stress-induced increases in hepatocyte transmembrane potential and resulted in 16% greater cell swelling compared with control. Calmodulin inhibitors trifluoperazine (100 mumol/L) and promethazine (100 mumol/L) inhibited the hyperpolarization of hepatocyte transmembrane potential caused by hyposmolality, as did 3,4,5-trimethoxybenzoate 8-(N,N-diethylamino)octyl ester) (50 mumol/L), which inhibits mobilization of Ca2+ from intracellular stores. Cytochalasin B (50 mumol/L), which disrupts microfilaments, also inhibited hyperpolarization of hepatocyte transmembrane potential with osmotic stress.(ABSTRACT TRUNCATED AT 250 WORDS)