Quantal Nature of Excitatory Synaptic Transmission in Cultured Hippocampal Cells of Rat and AMPAR Channel Kinetics

Abstract

Fast excitatory postsynaptic currents (EPSCS) mediated by glutamate arise from AMAPR channels in the membrane of cultured hippocampal cells in culture, incubated for 2-3 weeks after the cultural procedure of dissected cells from embryonic rat brain (E 17), were identified under Nomarski optics and investigated electrophysiologically. Whole-cell current recording using the patch-clamp technique revealed the synaptic currents ranging from less than 10 to more than 200 pA at a holding potential of −80 mV. These currents were blocked by 4μM CNQX, indicating that they results from the activation of postsynaptic AMPA receptor channels. Addition of tetrodotoxin (TTX, 1μM) resulted in the loss of most currents of more than 50 pA in amplitude. The currents, which disappeared after these treatments, were seemed to be the results of spontaneous presynaptic action potentials. Moreover, 2μM-bicuculline was added in order to eliminate the inhibitory postsynaptic currents (IPSC) that were mediated by GABAA receptor channels. The peak of spontaneous miniature EPSC amplitude histograms was asymmetrical and a tail of larger amplitude miniature EPSCs was observed. The decay time courses of miniature EPSCs were fitted with single exponential component. The histogram of the decay time constants also conformed to asymmetrical distribution with a tail of longer time constant.We also recorded the currents responses activated by (IR and/or UV) laser photolysis which have been already shown previously. It was shown that the miniature EPSCs and laser-evoked current responses have the similar physiological properties, which assumed that these currents are mediated by a AMPA receptor channel kinetics model that has been already presented.