Inhibition of the functional expression of N-methyl-D-aspartate receptors in a stably transformed cell line by cyclosporin A.

The L(tk-) cell line L12-G10 stably transformed with the human N-methyl-D-aspartate (NMDA) receptor subunits NR1-1a/NR2A showed a Ca(2+)-dependent increase in cell death, loss of mitochondrial membrane potential, and ATP depletion after agonist stimulation. Treatment of the cells with cyclosporine A (CsA) for 4h reduced glutamate-induced cell death by 60% (IC(50) of 7.1microM). The immunophilin binding drug FK506 was not effective. Short preincubation with CsA for 10 min already decreased the glutamate-induced loss of mitochondrial membrane potential while the NMDA receptor function is not affected. However, pretreatment of the cells with CsA (30 microM) for 6h reduced membrane associated NR1-1a protein amount by approximately 85%, whereas mRNA expression remained unaffected. These results suggest, that the cytoprotective effect of CsA in L12-G10 cells is due to the inhibition of the permeability transition pore on the one hand and to the inhibition of the expression of functional NMDA receptors by an additional posttranscriptional mechanism on the other hand.