Lukyanetz E A, Kostyuk P G
A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kiev, Ukraine.
Pflugers Arch. 1996 Jun;432(2):174-81. doi: 10.1007/s004240050121.
Previously we have reported that serotonin's (5-hydroxytryptamine or 5-HT) potentiating action on L-type Ca channels is present only in definite neurones from pedal ganglia of the mollusc Helix pomatia [Kostyuk PG, Lu kyanetz EA, Doroshenko PA (1992) Effects of serotonin and cAMP on calcium currents in different neurones of Helix pomatia. Pflügers Arch 420:9-15]. The potentiation is mediated by the cAMP second messenger system and is triggered by 5-HT1-like type receptors. To understand the physiological and pharmacological significance of this phenomenon, we analysed the comparative effects of dopamine (DA) and 5-HT on voltage-operated Ca currents (Ica) in isolated, intracellularly perfused H. pomatia neurones in whole- cell patch-clamp experiments. Two types of effects of DA (1-10 mircoM) and 5-HT (1-10 microM) on Ica were observed in different neurones: reversible inhibition (by about 40% and 20% respectively) or reversible potentiation (up to 65% and 40% respectively) of current amplitude. Neurones insensitive to neurotransmitter application were also observed. Da could induce potentiation of ica only in the same neurones that were similarly sensitive to 5-ht. However, a similar correlation between inhibitory action of neurotransmitters on Ica was not observed. The potentiating effects of 5-HT and DA on Ica were not additive and were mimicked by intracellular cAMP (100 microM) or 20 microgram/ml of the catalytic subunit of protein kinase A. We established that the potentiating effects of neurotransmitters were mediated by two distinct receptors, as the DA receptor antagonist ergometrin (1 microM) selectively inhibited the enhancement of Ica by DA and did not affect the action of 5-HT in the same cell. A similar specificity was observed for the dopaminergic compound, 5-chlortryptamine (10 microM), whereas the classical neuroleptic fluphenazine (10 microM) effectively blocked the 5-HT-evoked effect without significantly changing the action of DA. Methiothepin, an antagonist of 5-HT1 and 5-HT2 receptors, blocked both 5-HT-and DA-evoked effects. The results point out a possible convergence of the two different receptors (5-HT1-like and D1) on the same cAMP-dependent system of phosphorylation in the up-regulation of L-type Ca channel activity in mollusc neurones.
此前我们曾报道，血清素（5-羟色胺或5-HT）对L型钙通道的增强作用仅存在于软体动物苹果螺足神经节的特定神经元中[Kostyuk PG, Lukyanetz EA, Doroshenko PA（1992年）血清素和cAMP对苹果螺不同神经元钙电流的影响。《普弗吕格尔氏文献》420:9 - 15]。这种增强作用由cAMP第二信使系统介导，并由5-HT1样型受体触发。为了解这一现象的生理和药理意义，我们在全细胞膜片钳实验中分析了多巴胺（DA）和5-HT对分离的、细胞内灌注的苹果螺神经元电压门控钙电流（Ica）的比较作用。在不同神经元中观察到DA（1 - 10微摩尔）和5-HT（1 - 10微摩尔）对Ica有两种类型的作用：电流幅度的可逆性抑制（分别约为40%和20%）或可逆性增强（分别高达65%和40%）。也观察到对神经递质应用不敏感的神经元。DA仅能在对5-HT同样敏感的相同神经元中诱导Ica的增强。然而，未观察到神经递质对Ica抑制作用之间的类似相关性。5-HT和DA对Ica的增强作用不是相加的，并且可被细胞内cAMP（100微摩尔）或20微克/毫升的蛋白激酶A催化亚基模拟。我们确定神经递质的增强作用由两种不同的受体介导，因为DA受体拮抗剂麦角新碱（1微摩尔）选择性地抑制DA对Ica的增强作用，且不影响同一细胞中5-HT的作用。对于多巴胺能化合物5-氯色胺（10微摩尔）也观察到类似的特异性，而经典抗精神病药物氟奋乃静（10微摩尔）有效地阻断了5-HT诱发的效应，而没有显著改变DA的作用。甲硫哒嗪，一种5-HT1和5-HT2受体拮抗剂，阻断了5-HT和DA诱发的效应。结果指出在苹果螺神经元L型钙通道活性上调中，两种不同受体（5-HT1样和D1）可能在同一cAMP依赖性磷酸化系统上汇聚。
