Allosteric modulation of the presynaptic Ca2+ sensor for vesicle fusion.
Neurotransmitter release is triggered by an increase in the cytosolic Ca2+ concentration ([Ca2+]i), but it is unknown whether the Ca2+-sensitivity of vesicle fusion is modulated during synaptic plasticity. We investigated whether the potentiation of neurotransmitter release by phorbol esters, which target presynaptic protein kinase C (PKC)/munc-13 signalling cascades, exerts a direct effect on the Ca2+-sensitivity of vesicle fusion. Using direct presynaptic Ca2+-manipulation and Ca2+ uncaging at a giant presynaptic terminal, the calyx of Held, we show that phorbol esters potentiate transmitter release by increasing the apparent Ca2+-sensitivity of vesicle fusion. Phorbol esters potentiate Ca2+-evoked release as well as the spontaneous release rate. We explain both effects by an increased fusion 'willingness' in a new allosteric model of Ca2+-activation of vesicle fusion. In agreement with an allosteric mechanism, we observe that the classically high Ca2+ cooperativity in triggering vesicle fusion (approximately 4) is gradually reduced below 3 microM [Ca2+]i, reaching a value of <1 at basal [Ca2+]i. Our data indicate that spontaneous transmitter release close to resting [Ca2+]i is a consequence of an intrinsic property of the molecular machinery that mediates synaptic vesicle fusion.
Lou
Xuelin
X
AG Synaptische Dynamik und Modulation und Abt. Membranbiophysik, Max-Planck-Institut für biophysikalische Chemie, Am Fassberg 11, D-37077 Göttingen, Germany.
Scheuss
Volker
V
Schneggenburger
Ralf
R
D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D066298:In Vitro Techniques; D008561:Membrane Fusion / Q000187:drug effects; D008954:Models, Biological; D018377:Neurotransmitter Agents / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects
D018377:Neurotransmitter Agents; D015240:Phorbol 12,13-Dibutyrate; D002118:Calcium