Effects of general anesthetics on intercellular communications mediated by gap junctions between astrocytes in...

Astrocytes represent a major nonneuronal cell population in the central nervous system (CNS) and are actively involved in several brain functions. These cells are coupled by gap junctions (GJ) into a syncytial-like network resulting in cellular communication through ionic and metabolic exchange between adjacent astrocytes. Whether anesthetics affect astrocyte function is not known. In the present study, the effects of general anesthetics on GJ permeability were investigated in primary cultures of mouse striatal astrocytes.

Junctional permeability was determined by using the fluorescent probe Lucifer yellow and the scrape loading/dye transfer technique. Confluent cells were preincubated 5 min with various concentrations of anesthetic agents and GJ permeability was estimated by measuring the area occupied by the dye from digitalized images taken 8 min after cell loading.

Of the intravenous anesthetics tested, only propofol (P: 10(-4) M, P < 0.01 and 10(-5) M, P < 0.05) and etomidate (ET: 10(-4) M, P < 0.05, but not 10(-5) M) induced a significant reduction of GJ permeability. In contrast, diazepam (10(-5) M), morphine (10(-4) M), ketamine (10(-4) M), thiopental (10(-4) M), and clonidine (10(-7) M) did not affect junctional permeability. In addition, the halogenated anesthetics halothane, enflurane, and isoflurane induced a dose-dependent closure of GJ. For halothane, enflurane, and isoflurane, the maximum effect was achieved with a 10(-4) M, 1.6 x 10(-3) M, and 10(-3) M anesthetic concentration, respectively. Removal of volatile anesthetics resulted in the restoration of the control fluorescence area between 15 and 45 min. The time course of recovery of GJ permeability was examined more precisely for shorter periods of halothane administration (5 min, 1 mM). Under these conditions, the rate of dye spread returned to control values following anesthetic washout, while, during the same period of time, complete uncoupling of GJ was still observed in the presence of a 1 mM halothane concentration.

These results indicate that general anesthetics differentially affect GJ permeability in cultured astrocytes. This uncoupling effect (closure of gap junctions) may contribute to the mechanisms of action of some anesthetic agents (primarily volatile anesthetics) at the level of the CNS by altering astrocyte communication.