EXPRESSION OF CA2+-ION PERMEABLE ALPHA-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-permeability of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA) receptors from the human epileptic temporal lobe. Xenopus oocytes, injected with total RNA from the epileptic temporal lobe, were tested for expression of receptors by a conventional two electrode voltage-damp technique. Administration of glutamate and AMPA gave small or no clear current responses, whereas kainate produced large inward non-desensitizing currents. The current responses evoked by kainate were concentration dependent. Experimental data gave a Hill coefficient of 1.06 and an 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 mV (2 mM Ca2+) to 12 mV (60 mM Ba2+). This yielded a pBa(2+)/pK(+) permeability ratio of 1.6 when the constant field equation was used. The amplitude of the currents evoked by 600 mu M kainate in solutions containing higher Ba2+-ion concentrations was markedly diminished (46% in 10 mM Ba2+- and 75% in 60 mM Ba2+-solution), when compared to those obtained in normal Ringer's solution, suggesting interactions between different cation species and/or screening of surface charges.