Lax A J
J Cell Sci. 1979 Apr;36:311-21. doi: 10.1242/jcs.36.1.311.
Aggregation of Dictyostelium discoideum amoebae is effected by relayed cyclic AMP (cAMP) signals. The period of this wave propagation drops abruptly at the transition from aggregative to post-aggregative development. In this paper I demonstrate that the light-scattering response induced by a low concentration pulse of cAMP evolves from one lasting 5 min to one lasting 2 min. The definitive establishment of the 2-min response coincides with the beginning of post-aggregative gene expression. Amoebae at the aggregative stage are unable to respond to a second cAMP pulse delivered less than 4 min after the first, whereas at the post-aggregative stage they can respond to 2 pulses separated by 1 min or longer. Addition of cAMP phosphodiesterase to amoebae at the aggregative stage can in part mimic the change in excitable behaviour: the response is shortened and the amoebae can respond more frequently. However, the shortened response is not post-aggregative in shape and the prolonged presence of cyclic nucleotides induces different responses at the aggregative and post-aggregative stage. Both these results suggest that the rate of destruction of the relayed signal is not solely responsible for the change in excitability.
盘基网柄菌变形虫的聚集是由传递的环磷酸腺苷（cAMP）信号介导的。在从聚集发育向聚集后发育的转变过程中，这种波传播的周期会突然下降。在本文中，我证明了由低浓度cAMP脉冲诱导的光散射反应从持续5分钟演变为持续2分钟。2分钟反应的确立与聚集后基因表达的开始相吻合。聚集阶段的变形虫在第一个cAMP脉冲后不到4分钟就无法对第二个cAMP脉冲做出反应，而在聚集后阶段，它们可以对间隔1分钟或更长时间的两个脉冲做出反应。在聚集阶段的变形虫中添加cAMP磷酸二酯酶可以部分模拟兴奋行为的变化：反应缩短，变形虫可以更频繁地做出反应。然而，缩短后的反应在形状上并非聚集后阶段的反应，并且环核苷酸的长期存在在聚集阶段和聚集后阶段会诱导不同的反应。这两个结果都表明，传递信号的破坏速率并非兴奋性变化的唯一原因。
