EXPRESSION OF CA2-ION PERMEABLE PHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONATE (AMPA) RECEPTORS IN XENOPUS OOCYTES INJECTED WITH TOTAL RNA FROM HUMAN EPILEPTIC TEMPORAL-LOBE()

By using the Xenopus oocyte as an expression system, we have performed a series of experiments in order to examine the divalent cation-perme ability of ha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA) r eceptors from the human epileptic temporal lobe. Xenopus oocytes, inje cted with total RNA from the epileptic temporal lobe, were tested for expression of receptors by a conventional two electrode voltage-damp t echnique. Administration of glutamate and AMPA gave small or no clear current responses, whereas kainate produced large inward non-desensiti zing currents. The current responses evoked by kainate were concentrat ion dependent. Experimental data gave a Hill coefficient of 1.06 and a n EC(50) value of 87 mu M. The current to voltage relationship showed an inward rectification and when the concentration of divalent cations were enhanced, there was a shift in the reversal potential from -11 m V (2 mM Ca2+) to 12 mV (60 mM Ba2+). This yielded a pBa(2+)/pK(+) perm eability ratio of 1.6 when the constant field equation was used. The a mplitude of the currents evoked by 600 mu M kainate in solutions conta ining higher Ba2+-ion concentrations was markedly diminished (46% in 1 0 mM Ba2+- and 75% in 60 mM Ba2+-solution), when compared to those obt ained in normal Ringer's solution, suggesting interactions between dif ferent cation species and/or screening of surface charges.