EFFECTS OF STRONGLY ANISOSMOTIC AND NACL DEFICIENT SOLUTIONS ON MUSCIMOL AND GLUTAMATE EVOKED WHOLE-CELL CURRENTS IN FRESHLY DISSOCIATED HIPPOCAMPAL-NEURONS

Sudden exposure of dissociated hippocampal neurons to strongly hypo- o r hyperosmotic solutions suppresses voltage gated Na+, K+ and Ca2+ cur rents. We investigated whether ligand gated ion currents were similarl y shut down by exposure to anisosmotic solutions. The effect of hypo-o smotic, NaCl deficient (mannitol-substituted), or hyper-osmotic test s olutions delivered from a flow pipette was tested on voltage gated Ca2 + currents and on currents and conductance changes evoked by brief adm inistration of either the GABA(A)-agonist muscimol or glutamate. Hyper -osmotic solution caused cells to shrink, but cell membrane capacitanc e did not change. Muscimol-induced conductance increases were depresse d by hypo-osmotic and by NaCl deficient solutions and often by hyper-o smotic solution. Voltage gated Ca2+ currents were depressed by anisosm otic, but not by NaCl deficient isosmotic solution. NMDA- and non-NMDA evoked conductance increases were depressed by hyperosmotic solution; hypo-osmotic and NaCl deficient solutions were not tested on glutamat e induced currents. Ligand gated currents are suppressed by anisosmoti c solutions more slowly than are voltage gated channels. The changes c aused by anisosmotic and NaCl deficient solutions were much greater th en expected from calculated electrochemical effects and are probably t he result of change in receptor controlled channels.