Histamine H3-receptor-induced attenuation of norepinephrine exocytosis:: A decreased protein kinase A activity mediates a reduction in intracellular calcium
Histamine H3-receptor-induced attenuation of norepinephrine exocytosis:: A decreased protein kinase A activity mediates a reduction in intracellular calcium
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DOI：
10.1124/jpet.104.072504
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发表时间：
2005-01-01
影响因子：
3.5
通讯作者：
Levi, R
中科院分区：
文献类型：
--
作者：
Seyedi, N;Mackins, CJ;Levi, R
我们曾报道，突触前组胺H-3受体的激活抑制去极化心脏交感神经末梢的去甲肾上腺素胞吐作用，这一作用与神经元内Ca 2+的显著减少有关，我们将其归因于Ca 2+内流减少。H-3受体介导的cAMP依赖性Ca ~（2+）通道磷酸化的抑制可导致Ca ~（2+）内流、神经元内Ca ~（2+）和去甲肾上腺素胞吐的连续衰减。我们在表达天然H-3受体的交感神经末梢（心脏突触体）和用H-3受体转染的人神经母细胞瘤SH-SY 5 Y细胞中测试了这一假设。去甲肾上腺素胞吐引起的K+或刺激腺苷酸环化酶与毛喉素。H-3受体激活显着衰减K+和毛喉素诱导的去甲肾上腺素胞吐作用，百日咳毒素预处理防止这种效果。与毛喉素类似，8-溴-cAMP引起去甲肾上腺素胞吐，但与毛喉素不同，它不受H-3受体激活的影响，表明腺苷酸环化酶的抑制是H-3受体转导级联中的关键步骤。事实上，我们发现H-3-受体激活减弱去甲肾上腺素胞吐伴随着细胞内cAMP和PKA活性在SH-SY 5 Y-H-3细胞中的减少。此外，药理学PKA抑制与H-3受体激活协同作用，以减少K+诱导的SH-SY 5 YH（3）细胞内Ca 2+峰值和心脏突触体中去甲肾上腺素胞吐作用。此外，H-3-受体激活与N-和L-型钙通道阻滞剂协同作用，以减少心脏突触体中的去甲肾上腺素胞吐。我们的研究结果表明，H-3受体介导的抑制去甲肾上腺素从心脏交感神经胞吐的结果依次为H-3受体-G（i）/G（o）耦合，腺苷酸环化酶活性的抑制，减少cAMP的形成，导致PKA活性降低，从而减少通过电压操作的Ca ~（2+）通道的Ca ~（2+）内流。
We had reported that activation of presynaptic histamine H-3-receptors inhibits norepinephrine exocytosis from depolarized cardiac sympathetic nerve endings, an action associated with a marked decrease in intraneuronal Ca2+ that we ascribed to a decreased Ca2+ influx. An H-3-receptor-mediated inhibition of cAMP-dependent phosphorylation of Ca2+ channels could cause a sequential attenuation of Ca2+ influx, intraneuronal Ca2+ and norepinephrine exocytosis. We tested this hypothesis in sympathetic nerve endings ( cardiac synaptosomes) expressing native H-3-receptors and in human neuroblastoma SH-SY5Y cells transfected with H-3-receptors. Norepinephrine exocytosis was elicited by K+ or by stimulation of adenylyl cyclase with forskolin. H-3-receptor activation markedly attenuated the K+- and forskolin-induced norepinephrine exocytosis; pretreatment with pertussis toxin prevented this effect. Similar to forskolin, 8-bromo-cAMP elicited norepinephrine exocytosis but, unlike forskolin, it was unaffected by H-3-receptor activation, demonstrating that inhibition of adenylyl cyclase is a pivotal step in the H-3-receptor transductional cascade. Indeed, we found that H-3-receptor activation attenuated norepinephrine exocytosis concomitantly with a decrease in intracellular cAMP and PKA activity in SH-SY5Y-H-3 cells. Moreover, pharmacological PKA inhibition acted synergistically with H-3-receptor activation to reduce K+-induced peak intracellular Ca2+ in SH-SY5YH(3) cells and norepinephrine exocytosis in cardiac synaptosomes. Furthermore, H-3-receptor activation synergized with N- and L-type Ca2+ channel blockers to reduce norepinephrine exocytosis in cardiac synaptosomes. Our findings suggest that the H-3-receptor-mediated inhibition of norepinephrine exocytosis from cardiac sympathetic nerves results sequentially from H-3-receptor-G(i)/G(o) coupling, inhibition of adenylyl cyclase activity, and decreased cAMP formation, leading to diminished PKA activity, and thus, decreased Ca2+ influx through voltage-operated Ca2+ channels.