Chapin E M, Andrade R
Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI 48201, USA.
J Pharmacol Exp Ther. 2001 Apr;297(1):403-9.
Previous studies have shown that 5-hydroxytryptamine (5-HT) can modulate the hyperpolarization-activated nonselective cation current (I(h)) to elicit a membrane depolarization in neurons. However, the receptor subtype involved in this response remains controversial. In the accompanying study, we have identified a 5-HT7 receptor-mediated depolarization in the anterodorsal nucleus of the thalamus (ADn). In the present study, we have examined the possible role of I(h) in mediating this 5-HT7 receptor-mediated depolarization. We used the blind tight-seal patch clamp technique to examine the ability of 5-HT to modulate I(h) in the ADn. We found that 5-HT induced a shift in the voltage dependence of I(h) to more depolarized potentials. The pharmacology of the receptor mediating this effect was consistent with that of a 5-HT7 receptor. Since the 5-HT7 receptor is coupled positively to adenylate cyclase, we examined the cAMP dependence of the 5-HT-induced modulation of I(h). Intracellular addition of cAMP mimicked and occluded the 5-HT response. Conversely, in the presence of the protein kinase inhibitors H-8 and staurosporine, ADn neurons still expressed a 5-HT-induced shift in the voltage dependence of I(h). These results suggest that 5-HT regulates I(h) in the ADn through a cAMP-dependent but protein kinase A (PKA)-independent mechanism. To determine the contribution of I(h) to the 5-HT7 receptor-mediated depolarization, we used the selective I(h) blocker ZD7288. This compound greatly reduced the depolarizing response elicited by activation of 5-HT7 receptors. We conclude that 5-HT7 receptors depolarize ADn neurons primarily by increasing I(h) through a cAMP-dependent, PKA-independent mechanism.
先前的研究表明，5-羟色胺（5-HT）可调节超极化激活的非选择性阳离子电流（I(h)），从而在神经元中引发膜去极化。然而，参与该反应的受体亚型仍存在争议。在随附的研究中，我们已确定5-HT7受体介导丘脑前背核（ADn）的去极化。在本研究中，我们研究了I(h)在介导这种5-HT7受体介导的去极化中的可能作用。我们使用盲法全细胞膜片钳技术来检测5-HT调节ADn中I(h)的能力。我们发现5-HT使I(h)的电压依赖性向更去极化的电位偏移。介导这种效应的受体药理学与5-HT7受体一致。由于5-HT7受体与腺苷酸环化酶正性偶联，我们研究了5-HT诱导的I(h)调节的cAMP依赖性。细胞内添加cAMP模拟并阻断了5-HT反应。相反，在蛋白激酶抑制剂H-8和星形孢菌素存在的情况下，ADn神经元仍表现出5-HT诱导的I(h)电压依赖性偏移。这些结果表明，5-HT通过一种cAMP依赖性但蛋白激酶A（PKA）非依赖性机制调节ADn中的I(h)。为了确定I(h)对5-HT7受体介导的去极化的贡献，我们使用了选择性I(h)阻滞剂ZD7288。该化合物大大降低了5-HT7受体激活引发的去极化反应。我们得出结论：主要通过一种cAMP依赖性、PKA非依赖性机制增加I(h)，5-HT7受体使ADn神经元去极化。
