Moreno-Delgado David, Torrent Anna, Gómez-Ramírez Jordi, de Esch Iwan, Blanco Isaac, Ortiz Jordi
Universitat Autonoma de Barcelona, Neuroscience Institute and Department of Biochemistry and Molecular Biology, Bellaterra, Spain.
Neuropharmacology. 2006 Sep;51(3):517-23. doi: 10.1016/j.neuropharm.2006.04.010.
We previously described that agonist-activated histamine H3 autoreceptors inhibit the stimulation of histamine synthesis mediated by calcium/calmodulin- and cAMP-dependent protein kinases (CaMKII and PKA respectively) in histaminergic nerve endings. In the absence of an agonist H3 receptors show partial constitutive activity, so we hypothesized that suppression of constitutive activity by an inverse agonist could stimulate these transduction pathways. We show here that the H3 inverse agonist thioperamide increases histamine synthesis in rat brain cortical slices independently from the amounts of extracellular histamine. Thioperamide effects were mimicked by the inverse agonists clobenpropit and A-331440, but not by the neutral antagonist VUF-5681. In contrast, coincubation with VUF-5681 suppressed thioperamide effects. The effects of thioperamide were completely blocked by the PKA inhibitor peptide myristoyl-PKI14-22, a peptide that did not block depolarization stimulation of histamine synthesis. In addition, thioperamide effects required depolarization and were impaired by blockade of N-type calcium channels (mediating depolarization), but not by CaMKII inhibition. These results indicate that constitutive activity of H3 receptors in rat brain cortex inhibits the adenylate cyclase/PKA pathway, and perhaps also the opening of N-type voltage sensitive calcium channels, but apparently not CaMKII.
我们之前曾描述过，激动剂激活的组胺H3自身受体可抑制组胺能神经末梢中由钙/钙调蛋白依赖性蛋白激酶（分别为CaMKII和PKA）介导的组胺合成刺激。在没有激动剂的情况下，H3受体表现出部分组成性活性，因此我们推测反向激动剂对组成性活性的抑制可能会刺激这些转导途径。我们在此表明，H3反向激动剂硫代丙酰胺可独立于细胞外组胺的量增加大鼠脑皮质切片中的组胺合成。反向激动剂氯苯丙胺和A-331440可模拟硫代丙酰胺的作用，但中性拮抗剂VUF-5681则不能。相反，与VUF-5681共同孵育可抑制硫代丙酰胺的作用。硫代丙酰胺的作用被PKA抑制剂肽肉豆蔻酰-PKI14-22完全阻断，该肽不会阻断组胺合成的去极化刺激。此外，硫代丙酰胺的作用需要去极化，并且会因N型钙通道（介导去极化）的阻断而受损，但不会因CaMKII抑制而受损。这些结果表明，大鼠脑皮质中H3受体的组成性活性抑制腺苷酸环化酶/PKA途径，也可能抑制N型电压敏感性钙通道的开放，但显然不抑制CaMKII。
