EFFECTS OF GENERAL-ANESTHETICS ON INTERCELLULAR COMMUNICATIONS MEDIATED BY GAP-JUNCTIONS BETWEEN ASTROCYTES IN PRIMARY CULTURE

Background. Astrocytes represent a major nonneuronal cell population i n the central nervous system (CNS) and are actively involved in severa l brain functions. These cells are coupled by gap junctions (GJ) into a syncytial-like network resulting in cellular communication through i onic and metabolic exchange between adjacent astrocytes. Whether anest hetics affect astrocyte function is not known. In the present study, t he effects of general anesthetics on GJ permeability were investigated in primary cultures of mouse striatal astrocytes. Methods. Junctional permeability was determined by using the fluorescent probe Lucifer ye llow and the scrape loading/dye transfer technique. Confluent cells we re preincubated 5 min with various concentrations of anesthetic agents and GJ permeability was estimated by measuring the area occupied by t he dye from digitalized images taken 8 min after cell loading. Results : 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, bu t not 10(-3)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 junctiona l permeability. In addition, the halogenated anesthetics halothane, en flurane, and isoflurane induced a dose-dependent closure of GJ. For ha lothane, enflurane, and isoflurane, the maximum effect was achieved wi th a 10(-4)M, 1.6 x 10(-3)M, and 10(-3)M anesthetic concentration, res pectively. Removal of volatile anesthetics resulted in the restoration of the control fluorescence area between 15 and 45 min. The time cour se of recovery of GJ permeability was examined more precisely for shor ter periods of halothane administration (5 min, 1 mm). Under these con ditions, the rate of dye spread returned to control values following a nesthetic washout, while, during the same period of time, complete unc oupling of GJ was still observed in the presence of a 1 mm halothane c oncentration. Conclusions. These results indicate that general anesthe tics differentially affect GJ permeability in cultured astrocytes. Thi s uncoupling effect (closure of gap junctions) may contribute to the m echanisms of action of some anesthetic agents (primarily volatile anes thetics) at the level of the CNS by altering astrocyte communication.