A quantitative measurement of the dependence of short-term synaptic enhancement on presynaptic residual calcium

摘要: We simultaneously measured presynaptic free calcium ion concentration ([Ca2+]i) and synaptic strength at the crayfish claw opener neuromuscular junction (nmj) under a variety of experimental conditions. Our experiments were designed both to test hypothesis that elevated [Ca2+]i is necessary sufficient for induction form enhancement persists several seconds after tetanic stimulation--augmentation--and determine quantitative relationship between this enhancement. Action potential trains increased enhanced transmission. During decay phase known as augmentation (time constant approximately 7 sec 20 degrees C with < 200 microM fura-2 in terminals), was 700 nM or less above rest an essentially linear observed. Introduction exogenous Ca2+ buffers into terminal slowed buildup recovery kinetics component corresponding augmentation. The slope relating delta not changed. time course remained correlated temperature preparation changed from about 10 C, but more than two- threefold. moderate frequency action potentials, slowly developing total linearly related residual fura-2. during same trains.(ABSTRACT TRUNCATED AT 250 WORDS)