Summation of GABA- and Glutamate-Mediated Ion Currents in Isolated Rat Cerebral Cortex Neurons

Abstract

Patch clamp experiments in the whole cell configuration were performed on isolated rat prefrontal cortex neurons to study the summation of ion currents evoked by application of glutamate and GABA. Ion currents were recorded using two different pipette solutions, based on cesium chloride and fluoride. In recordings made using the cesium chloride-based solution, the peak amplitude of the current evoked by simultaneous application of GABA and glutamate (each at 200 μM) coincided with the peak amplitude of the current evoked by application of GABA alone, and was significantly smaller than the arithmetic sum of the responses to application of the two neurotransmitters individually. When the pipette solution based on cesium fluoride was used, the response to simultaneous application of glutamate and GABA was essentially the same as the arithmetic sum of the individual responses. On exposure to these neurotransmitters at saturating concentrations (5 mM), the response recorded to simultaneous application was significantly smaller than the response to application of GABA alone. These results suggest that there is a mechanism of interaction between GABAA and ionotropic glutamate receptors (AMPA and kainate). On simultaneous application of glutamate and GABA, activation of GABAA receptors evidently has a greater influence on glutamate receptors than activation of glutamate receptors of GABAA receptors.