title: Hypertonic stress increases the Na+ conductance of rat hepatocytes in primary culture.
abstract: We studied the ionic mechanisms underlying the regulatory volume increase of rat hepatocytes in primary culture by use of confocal laser scanning microscopy, conventional and ion-sensitive microelectrodes, cable analysis, microfluorometry, and measurements of 86Rb+ uptake. Increasing osmolarity from 300 to 400 mosm/liter by addition of sucrose decreased cell volumes to 88.6% within 1 min; thereafter, cell volumes increased to 94.1% of control within 10 min, equivalent to a regulatory volume increase (RVI) by 44.5%. This RVI was paralleled by a decrease in cell input resistance and in specific cell membrane resistance to 88 and 60%, respectively. Ion substitution experiments (high K+, low Na+, low Cl-) revealed that these membrane effects are due to an increase in hepatocyte Na+ conductance. During RVI, ouabain-sensitive 86Rb+ uptake was augmented to 141% of control, and cell Na+ and cell K+ increased to 148 and 180%, respectively. The RVI, the increases in Na+ conductance and cell Na+, as well as the activation of Na+/K(+)-ATPase were completely blocked by 10(-5) mol/liter amiloride. At this concentration, amiloride had no effect on osmotically induced cell alkalinization via Na+/H+ exchange. When osmolarity was increased from 220 to 300 mosm/liter (by readdition of sucrose after a preperiod of 15 min in which the cells underwent a regulatory volume decrease, RVD) cell volumes initially decreased to 81.5%; thereafter cell volumes increased to 90.8% of control. This post-RVD-RVI of 55.0% is also mediated by an increase in Na+ conductance. We conclude that rat hepatocytes in confluent primary culture are capable of RVI as well as of post-RVD-RVI. In this system, hypertonic stress leads to a considerable increase in cell membrane Na+ conductance. In concert with conductive Na+ influx, cell K+ is then increased via activation of Na+/K(+)-ATPase. An additional role of Na+/H+ exchange in the volume regulation of rat hepatocytes remains to be defined.
authors.affiliation: Max-Planck-Institut für molekular Physiologie, Abteilung Epithelphysiologie, Dortmund, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Wehner
authors.forename: H
authors.initials: H
authors.lastname: Sauer
authors.forename: R K
authors.initials: RK
authors.lastname: Kinne
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006982:Hypertonic Solutions / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008839:Microelectrodes; D018613:Microscopy, Confocal; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012414:Rubidium Radioisotopes; D015222:Sodium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013312:Stress, Physiological / Q000378:metabolism*
chemical_list: D018118:Chloride Channels; D006982:Hypertonic Solutions; D012414:Rubidium Radioisotopes; D015222:Sodium Channels; D000254:Sodium-Potassium-Exchanging ATPase