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Thiocyanate ions selectively antagonize AMPA-evoked responses in Xenopus laevis oocytes microinjected with rat brain
Abstract:
1 Responses to kainate (KA), willardiine and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were recorded from rat brain mRNA-injected Xenopus laevis oocytes by use of a two-electrode voltage clamp. 2 Thiocyanate (SCN-; 50 microM-4 mM) ions reversibly and selectively inhibited the membrane current responses to AMPA in a non-competitive manner without affecting KA or willardiine-induced responses. 3 The inhibition of AMPA-induced responses by SCN- was dependent on the SCN- concentration with an estimated IC50 of 1 mM. The antagonism was not dependent on the AMPA concentration. 4 The response to a high concentration of AMPA (100-200 microM) exhibited a peak inward current which declined to a steady-state. SCN- inhibited the steady-state current more than the peak response. The inhibition was unaffected by prior incubation with concanavalin-A (Con-A; 10 microM). 5 Responses to KA were antagonized by AMPA in a competitive manner, suggesting that both agonists may activate a common receptor-channel complex. This interaction between two non-NMDA agonists was not affected by the SCN(-)-induced inhibition of the AMPA response. 6 AMPA-induced responses recorded from large cultured cerebellar neurones by whole-cell recording were also inhibited by SCN- in a non-competitive manner. The AMPA-induced peak current was less affected than the steady-state response. 7 We conclude that SCN- can inhibit the response to AMPA in expressed non-NMDA receptors in Xenopus oocytes and also in native receptors in cultured cerebellar neurones. One possible mechanism of action for SCN- inhibition of responses to AMPA may involve a Con-A-insensitive, non-NMDA receptor-mediated desensitization.
Insights
Thiocyanate ions selectively inhibit alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor responses in Xenopus oocytes and cerebellar neurons. This non-competitive inhibition affects steady-state currents more than peak responses.
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Non-NMDA receptors, including kainate (KA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, are crucial for excitatory neurotransmission in the brain.
- Understanding the modulation of these receptors by ions is essential for deciphering neuronal signaling and developing therapeutic strategies.
Purpose of the Study:
- To investigate the effect of thiocyanate (SCN-) ions on AMPA and KA receptor activity.
- To determine the mechanism and selectivity of SCN- inhibition on non-NMDA receptor-mediated currents.
Main Methods:
- Xenopus laevis oocytes were injected with rat brain mRNA encoding non-NMDA receptors.
- Two-electrode voltage clamp electrophysiology was used to record responses to AMPA, KA, and willardiine.
- Whole-cell recording was performed on cultured cerebellar neurons to assess SCN- effects on native receptors.
Main Results:
- Thiocyanate (SCN-) selectively and reversibly inhibited AMPA-induced currents in a non-competitive manner (IC50 ≈ 1 mM) without affecting KA or willardiine responses.
- SCN- inhibited the steady-state current more than the peak current of AMPA responses, an effect independent of AMPA concentration and concanavalin-A.
- AMPA competitively antagonized KA responses, indicating a shared receptor-channel complex, and SCN- did not affect this interaction.
Conclusions:
- SCN- acts as a non-competitive inhibitor of AMPA-induced currents in both expressed non-NMDA receptors in Xenopus oocytes and native receptors in cerebellar neurons.
- The findings suggest a potential mechanism involving SCN- inducing a concanavalin-A-insensitive, non-NMDA receptor-mediated desensitization.
- SCN- offers a selective pharmacological tool for studying AMPA receptor function and desensitization.