Activation of pre-synaptic M-type K+ channels inhibits [ 3H]d-aspartate release by reducing Ca2+ entry through P/Q-type voltage-gated Ca2+channels

Abstract

In this study, the functional consequences of the pharmacological modulation of the M-current (IKM) on cytoplasmic Ca2+ intracellular Ca2+concentration ([Ca2+]i) changes and excitatory neurotransmitter release triggered by various stimuli from isolated rat cortical synaptosomes have been investigated. Kv7.2 immunoreactivity was identified in pre-synaptic elements in cortical slices and isolated glutamatergic cortical synaptosomes. In cerebrocortical synaptosomes exposed to 20 mM [K+]e, the IKM activator retigabine (RT, 10 μM) inhibited [3H]d-aspartate ([ 3H]d-Asp) release and caused membrane hyperpolarization; both these effects were prevented by the IKM blocker XE-991 (20 μM). The IKM activators RT (0.1-30 μM), flupirtine (10 μM) and BMS-204352 (10 μM) inhibited 20 mM [K+]e-induced synaptosomal [Ca2+]i increases; XE-991 (20 μM) abolished RT-induced inhibition of depolarization-triggered [Ca 2+]i transients. The P/Q-type voltage-sensitive Ca 2+channel (VSCC) blocker ω-agatoxin IVA prevented RT-induced inhibition of depolarization-induced [Ca2+]i increase and [3H]d-Asp release, whereas the N-type blocker ω-conotoxin GVIA failed to do so. Finally, 10 μM RT did not modify the increase of [Ca 2+]i and the resulting enhancement of [3H]d-Asp release induced by [Ca2+]i mobilization from intracellular stores, or by store-operated Ca2+channel activation. Collectively, the present data reveal that the pharmacological activation of IKM regulates depolarization-induced [3H]d-Asp release from cerebrocortical synaptosomes by selectively controlling the changes of [Ca2+]i occurring through P/Q-type VSCCs. © 2009 International Society for Neurochemistry.