N-ethylmaleimide increases release probability at GABAergic synapses in layer I of the mouse visual cortex.
The sulphydryl alkylating agent N-ethylmaleimide (NEM) has been often used as an uncoupler of pertussis toxin-sensitive G-proteins. However, the effects of NEM on gamma-aminobutyric acid (GABA)ergic synaptic transmission remain controversial. Using the whole-cell patch-clamp technique, GABA(A) receptor-mediated postsynaptic currents (IPSCs) have been recorded from Cajal-Retzius (CR) cells in layer I of the neonatal mouse visual cortex. NEM increased the frequencies of both spontaneous and miniature IPSCs (mIPSCs) without an effect on the median mIPSC amplitudes or mIPSC kinetics. The NEM actions on mIPSCs did not depend on the extracellular Ca(2+), Ca(2+) release from intracellular stores, adenylyl cyclase and protein kinase A activities. NEM increased the mean amplitudes of evoked IPSCs and strongly decreased the paired-pulse ratio. The size of the readily releasable pool of presynaptic vesicles (RRP) was estimated using a high-frequency stimulation protocol. The RRP size was not affected by NEM. In addition, NEM significantly decreased the latency between the stimulus and the onset of GABA release. These results suggest that NEM selectively increases GABA release probability. At postnatal day 2, mIPSCs were observed only in about 30% of CR cells. NEM application revealed, however, that more than 90% of CR cells receive GABAergic inputs. Therefore, NEM seems to be a useful tool to verify the existence of 'silent' GABAergic synapses.
Kirmse
Knut
K
Sensory and Developmental Physiology Group, Institute of Neurophysiology, Johannes-Mueller-Center of Physiology, Charité-University Medicine Berlin, Berlin, Germany.
Kirischuk
Sergei
S
D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005033:Ethylmaleimide / Q000494:pharmacology*; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D018408:Patch-Clamp Techniques / Q000379:methods; D011336:Probability; D013569:Synapses / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D013997:Time Factors; D014793:Visual Cortex / Q000166:cytology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005680:gamma-Aminobutyric Acid; D005033:Ethylmaleimide