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Zusammenfassung:
Synaptic efÞcacy critically depends on the presynaptic intracellular calcium concentration ([Ca21]i). We measured the calcium sensitivity of glutamate release in a rat auditory brainstem synapse by laser photolysis of caged calcium. A rise in [Ca21]i to 1 micromolar readily evoked release. An increase to .30 micromolar depleted the releasable vesicle pool in ,0.5 millisecond. A comparison with action potentialÐevoked release suggested that a brief increase of [Ca21]i to ;10 micromolar would be sufÞcient to reproduce the physiological release pattern. Thus, the calcium sensitivity of release at this synapse is high, and the distinction between phasic and delayed release is less pronounced than previously thought.
