Sugita S, Baxter D A, Byrne J H
Department of Neurobiology and Anatomy, The University of Texas Medical School at Houston, Houston, Texas 77225, USA.
J Neurosci. 1997 Oct 1;17(19):7237-44. doi: 10.1523/JNEUROSCI.17-19-07237.1997.
The synaptic connections between the sensory neurons of Aplysia and their follower neurons have been used as a model system for examining the cellular mechanisms contributing to neuronal and synaptic plasticity. Recent studies suggest that at least two protein kinases, protein kinase A (PKA) and protein kinase C (PKC), contribute to serotonin (5-HT)-induced short-term facilitation. The interaction between these two kinase cascades has not been examined, however. Using electrophysiological and biochemical approaches, we examined possible interactions between PKA and PKC cascades. The results indicated that prolonged activation of PKC by preincubation with phorbol esters attenuated PKA-mediated actions of 5-HT, including increases in sensory neuron excitability and spike broadening in the presence of tetraethylammonium (TEA) and nifedipine. Although phorbol esters also attenuated increases in excitability by an analog of cAMP and small cardioactive peptide B (SCPB), the degree of attenuation was smaller. In addition, phorbol esters did not attenuate broadening of TEA spikes by the cAMP analog and SCPB. Thus, phorbol esters appeared specifically to attenuate aspects of the 5-HT activation of the cAMP/PKA cascade. Measurements of cAMP levels with radioimmunoassays revealed that phorbol esters did not attenuate 5-HT-induced cAMP synthesis, however. Finally, the results indicated that phorbol esters themselves induced a small but significant increase in excitability as well as an increase in the level of cAMP. Our results suggest that there is crosstalk between the PKC and PKA cascades. The mechanisms by which phorbol esters specifically attenuate 5-HT-induced activation of the cAMP/PKA cascade are not known, however.
海兔的感觉神经元与其后续神经元之间的突触连接已被用作一个模型系统，用于研究促成神经元和突触可塑性的细胞机制。最近的研究表明，至少两种蛋白激酶，即蛋白激酶A（PKA）和蛋白激酶C（PKC），促成了5-羟色胺（5-HT）诱导的短期易化。然而，尚未对这两种激酶级联之间的相互作用进行研究。我们使用电生理学和生物化学方法，研究了PKA和PKC级联之间可能的相互作用。结果表明，通过与佛波酯预孵育对PKC进行长时间激活，会减弱PKA介导的5-HT作用，包括感觉神经元兴奋性的增加以及在存在四乙铵（TEA）和硝苯地平的情况下动作电位展宽。尽管佛波酯也会减弱由环磷酸腺苷（cAMP）类似物和小的心脏活性肽B（SCPB）引起的兴奋性增加，但减弱程度较小。此外，佛波酯不会减弱由cAMP类似物和SCPB引起的TEA动作电位展宽。因此，佛波酯似乎特异性地减弱了5-HT对cAMP/PKA级联的激活作用。通过放射免疫测定法对cAMP水平的测量显示，佛波酯不会减弱5-HT诱导的cAMP合成。最后，结果表明佛波酯本身会引起兴奋性的小幅但显著增加以及cAMP水平的增加。我们的结果表明PKC和PKA级联之间存在相互作用。然而，佛波酯特异性减弱5-HT诱导的cAMP/PKA级联激活的机制尚不清楚。
