Terrian D M
Department of Anatomy and Cell Biology, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354.
J Neurochem. 1995 Jan;64(1):172-80. doi: 10.1046/j.1471-4159.1995.64010172.x.
Sustained activation of protein kinase C significantly enhanced a secondary (slow) phase in the depolarization-induced release of glutamate from isolated hippocampal nerve endings. The phorbol ester, 4 beta-phorbol 12,13-dibutyrate, was used to sustain the activation of presynaptic protein kinase C for a prolonged (10-min) period, and then this relatively water-soluble phorbol ester was removed by superfusion before a 2-min stimulus of continuous membrane depolarization. These conditions were used to investigate the persistent effects of sustained protein kinase C activation on the magnitude of the slow phase of evoked glutamate release, in which the efficiency of synaptic vesicle mobilization and recycling may be primary determinants of response magnitude. It is reported here that sustained protein kinase C activation selectively increased the Ca(2+)-dependent component of glutamate release during a prolonged phase of K(+)-induced depolarization. The magnitude of this persistent effect on Ca(2+)-dependent glutamate release was directly related to the dose of 4 beta-phorbol 12,13-dibutyrate and the duration of exposure that was used to prime the release apparatus, was observed using two alternative synaptosomal preparations, and was evident regardless of the depolarizing stimulus used (elevated [KCl] or 4-aminopyridine). However, 4 beta-phorbol 12,13-dibutyrate did not alter the release induced by the Ca2+ ionophore ionomycin. Thus, the persistent effects of protein kinase C activation on a prolonged phase of glutamate release were dependent on the route of Ca2+ influx. The finding that voltage-regulated Ca2+ channel blockers were able to neutralize completely the 4 beta-phorbol 12,13-dibutyrate-dependent facilitation of K(+)-evoked glutamate release provided further support for this conclusion.(ABSTRACT TRUNCATED AT 250 WORDS)
蛋白激酶C的持续激活显著增强了离体海马神经末梢去极化诱导的谷氨酸释放的第二（缓慢）时相。佛波酯4β-佛波醇12,13-二丁酸酯用于使突触前蛋白激酶C持续激活较长时间（10分钟），然后在持续膜去极化2分钟刺激之前通过灌流去除这种相对水溶性的佛波酯。这些条件用于研究蛋白激酶C持续激活对诱发的谷氨酸释放缓慢时相幅度的持续影响，其中突触小泡动员和再循环的效率可能是反应幅度的主要决定因素。本文报道，在K⁺诱导的去极化延长阶段，蛋白激酶C的持续激活选择性地增加了谷氨酸释放的Ca²⁺依赖性成分。这种对Ca²⁺依赖性谷氨酸释放的持续影响幅度与4β-佛波醇12,13-二丁酸酯的剂量以及用于启动释放装置的暴露持续时间直接相关，在两种不同的突触体准备中均观察到，并且无论使用何种去极化刺激（升高的[KCl]或4-氨基吡啶）都很明显。然而，4β-佛波醇12,13-二丁酸酯并未改变Ca²⁺离子载体离子霉素诱导的释放。因此，蛋白激酶C激活对谷氨酸释放延长阶段的持续影响取决于Ca²⁺内流途径。电压调节性Ca²⁺通道阻滞剂能够完全中和4β-佛波醇12,13-二丁酸酯依赖性的K⁺诱发的谷氨酸释放促进作用，这一发现为该结论提供了进一步支持。（摘要截短至250字）
