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Lead-induced blockage of kainate-sensitive receptor channels
U Musshoff1, M Madeja, N Binding
1Institut fur Physiologie, Münster, Germany.
Abstract:
The effects of bivalent lead on ion channels activated by kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionate (AMPA) were studied using Xenopus oocytes microinjected with mRNA from rat brain. Lead reduced kainate-induced membrane currents in a reversible and dose-dependent manner, without affecting membrane currents induced by AMPA. Lead decreased the kainate currents with a concentration of 0.1 micromol/1 to 0.93 +/- 0.01 and with a concentration of 100 micromol/1 to 0.41 +/- 0.04 of the control values. The blocking effect of lead on kainate responses was voltage dependent. The inhibition was strongest at -90 mV to -70 mV and became weaker at more positive membrane potentials. The effect of lead on the kainate-induced membrane currents remained unchanged when the concentration of kainate was increased. Hence lead probably represents a noncompetitive channel-blocking agent for non-N-methyl-D-aspartate (NMDA) receptor channels activated by kainate.
Insights
Bivalent lead exposure inhibits kainate receptor channels, crucial for brain signaling, but not AMPA receptor channels. This lead-induced blockage is dose-dependent and voltage-sensitive, impacting neurotransmission.
Area of Science:
- Neuroscience
- Toxicology
- Molecular Biology
Background:
- Ion channels are vital for neuronal communication.
- Kainate and AMPA receptors are key excitatory glutamate receptors.
- Lead is a neurotoxicant with known effects on the nervous system.
Purpose of the Study:
- To investigate the impact of bivalent lead on kainate and AMPA receptor function.
- To characterize the mechanism of lead's interaction with these ion channels.
Main Methods:
- Xenopus oocytes were microinjected with rat brain mRNA encoding kainate and AMPA receptors.
- Electrophysiological recordings were used to measure ion channel currents.
- Dose-response and voltage-dependence studies were conducted with lead exposure.
Main Results:
- Lead reversibly inhibited kainate-activated currents in a dose-dependent manner.
- Lead did not affect AMPA-activated currents.
- The inhibitory effect of lead on kainate currents was voltage-dependent, strongest at negative potentials.
- Lead's action was independent of kainate concentration, suggesting noncompetitive antagonism.
Conclusions:
- Bivalent lead acts as a noncompetitive blocker of kainate-activated non-NMDA receptor channels.
- Lead selectively targets kainate receptors, potentially disrupting glutamatergic neurotransmission.
- These findings contribute to understanding lead's neurotoxic mechanisms.