GABA(A) RECEPTOR-MEDIATED CURRENTS IN INTERNEURONS AND PYRAMIDAL CELLS OF RAT VISUAL-CORTEX

1. We compared gamma-aminobutyric acid (GABA)-mediated responses of id entified pyramidal cells and fast spiking interneurons in layer V of v isual cortical slices from young rats (P11-14). 2. The frequency of sp ontaneous inhibitory postsynaptic currents (sIPSCs) was similar in pyr amidal cells and interneurons (1.7 vs. 1.9 Hz). For events with 10-90% rise times less than 0.9 ms, no significant differences were found in mean amplitude (61 vs. 65 pA), mean rise time (0.58 vs. 0.61 ms), or the first time constant of decay (tau(1), 6.4 vs. 6.5 ms) between pyra midal cells and interneurons. The second decay time constant (tau(2)) was significantly longer in interneurons than in pyramidal cells (49 v s. 22 ms). The difference in sIPSC decay kinetics between two cell typ es also existed in adult rats (P36-42), suggesting the kinetic differe nce is not due to differential development of GABA(A) receptors in the se cell types. 3. The decay kinetics of monosynaptic evoked IPSCs were also longer in interneurons. As in the case of sIPSCs, the difference was accounted for by the second decay time constant. tau(1) and tau(2 ) were, respectively, 13 and 64 ms for interneurons and 12 and 47 ms f or pyramidal cells. 4. Cell-attached patch recordings revealed that th e mean open time for single Cl- channels in response to 2 mu M GABA wa s significantly longer in interneurons than pyramidal cells (5.0 vs. 2 .8 ms). The chord conductance of these channels in interneurons (12 pS ) was significantly smaller than in pyramidal cells (15 pS). Single ch annel currents reversed polarity when the pipette potential was approx imately -10 mV for both cell types. 5. These results show that there i s a functional diversity of GABA(A) receptors in electrophysiologicall y and morphologically identified cortical pyramidal cells and interneu rons. This diversity might derive from the different molecular composi tion of the receptors in these two cell types.