The neuroprotective compounds riluzole, minocycline, and memantine interact with AMPA-type glutamate receptors: a patch clamp study

Antagonizing glutamatergic neurotransmission by blockade of AMPA-type glutamate receptors is a promising pharmacological strategy in the treatment of chronic neurodegenerative diseases. We performed the patch-clamp technique in combination with an ultrafast solution exchange system to investigate the interaction of riluzole, minocycline and memantine with recombinant AMPA-type glutamate receptor channels.

Homooligomeric GluR2flipGQ or non-desensitizing GluR2 L504Y channels were expressed in HEK293 cells. We conducted experiments following coapplication and preincubation protocols for the respective test compound while current transients were elicited by pulswise application of saturating concentrations of the agonist glutamate.

When minocycline was coapplied with glutamate, an open channel block was observed at nondesensitizing GluR2L504Y channels. The relative area under the current curve (rAUC), relative steady state current (rCdes), and time constant of current decay decreased significantly at 1 mM or 3 mM minocycline. Dose-dependently increasing reopening currents were also observed. However, with GluR2flipGQ channels minocycline showed a slight enhancemet of membrane currents.

Block effect of riluzole was observed in preincubation experiments. A dose-dependent decrease of the maximal current amplitude and the rAUC was found after preincubation with 0,1 mM or higher concentracions of riluzole. That points to a competitive block mechanism. Coapplication experiments on GluR2L504Y with 1 or 3 mM riluzole showed a decrease of the time constant of current decay. Reopening currents after coapplication with 3 mM riluzole were also observed. These kinetic findings points out an open-channel block mechanism.

The block mechanism induced by memantine can be described as an open-channel block. The rAUC, rCdes, and time constant of current decay decreased dose-dependently. When 1 mM memantine was coapplied, the peak of the reopening current was 57 + 14% of the maximum peak current amplitude.

Conclusion:

1. Minocycline shows a direct interaction with AMPA receptor channels. A current enhancement and an open-channel block were observed at a high concentration range. For the non-desensitizing GluR2L504Y receptor channel, only the open-channel block was observed.

2. Riluzole modulates AMPA receptors dose-dependently via a competitive block and additionally an open-channel block.

3. Memantine interacts with AMPA receptor channels via an open channel block mechanism.