Facilitation of presynaptic calcium currents in the rat brainstem.
1. To study use-dependent changes in the presynaptic Ca2+ influx and their contribution to transmitter release, we made simultaneous voltage clamp recordings from presynaptic terminals (the calyces of Held) and postsynaptic cells (the principal cells of the medial nucleus of the trapezoid body) in slices of the rat auditory brainstem. 2. Following a short (2 ms) prepulse to 0 mV, calcium channels opened faster during steps to negative test potentials. During trains of action potential waveforms the Ca2+ influx per action potential increased. At the same time, however, the amplitude of the EPSCs decreased. 3. The facilitation of the calcium currents appeared to depend on a build-up of intracellular Ca2+, since its magnitude was proportional to the Ca2+ influx and it was reduced in the presence of 10 mM BAPTA. 4. Facilitation of the presynaptic calcium currents may contribute to short-term facilitation of transmitter release, observed when quantal output is low. Alternatively, it may counteract processes that contribute to synaptic depression.
Abteilung Zellphysiologie, Max-Planck-Institut fur medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany. borst@sunny.mpimf-heidelberg.mpg.de
J G
JG
Borst
B
B
Sakmann
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D015220:Calcium Channels; D005456:Fluorescent Dyes; D018377:Neurotransmitter Agents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D016257:Fura-2