Osmolarity reduction transiently increases K+ conductance of confluent rat hepatocytes in primary culture.

Abstract

Rat hepatocytes in confluent primary cultures were impaled with conventional microelectrodes. Reducing extracellular osmolarity by 80 mosmol/l leads to a transient hyperpolarization of cell membranes (maximum after 5 min) from -40 +/- 4 to -51 +/- 2 mV (n = 7). This hyperpolarization is blocked by 1 mmol/l Ba2+ and 0.5 mmol/l quinine. In ion substitution experiments, increasing K+ 10-fold (from 2.7 to 27 mmol/l) depolarizes membrane voltage by 9 +/- 2 mV in normosmotic solutions. In hyposmotic solutions this depolarization is increased to 20 +/- 1 mV at the time of maximum hyperpolarization and decreases thereafter to 8 +/- 2 mV (n = 4). Cable analysis reveals a transient decrease of specific membrane resistance that exactly parallels the increase in membrane voltage response to high K+. In addition, electrical coupling between cells continuously decreases under hyposmotic conditions, indicating that intercellular communication is affected. Reducing Cl- 100-fold (from 116.5 to 1.2 mmol/l; HCO(3-)-free solutions) depolarizes hepatocytes by 24 +/- 3 mV under normosmotic conditions. In hyposmotic solutions, this effect is increased to 39 +/- 4 mV at maximum hyperpolarization and decreases again to 26 +/- 3 mV (n = 8). This transient increase in the voltage response to Cl- removal is abolished by 0.5 mmol/l quinine (n = 5) and 1 mmol/l Ba2+ (n = 5), suggesting that it is indirect via changes in K+ conductance. This concept is corroborated by ion substitution experiments (HCO(3-)-free conditions), which show that under hyposmotic conditions voltage response to high K+ is considerably decreased in low Cl- solutions.(ABSTRACT TRUNCATED AT 250 WORDS)