Chik C L, Liu Q Y, Li B, Klein D C, Zylka M, Kim D S, Chin H, Karpinski E, Ho A K
Department of Medicine, University of Alberta, Edmonton, Canada.
J Neurochem. 1997 Mar;68(3):1078-87.
In this study the subunits of the dihydropyridine-sensitive L-type Ca2+ channels (L-channels) expressed in rat pinealocytes were characterized using reverse transcription (RT)-PCR analysis, and the modulation of these channels by adrenergic agonists and by pituitary adenylate cyclase-activating polypeptide (PACAP) was studied using the patch-clamp technique. RT-PCR analysis showed that rat pinealocytes expressed alpha 1D, alpha 2b, beta 2, and beta 4 Ca(2+)-channel subunit mRNAs. Other alpha 1 subunit transcripts were either not expressed or present at very low levels, indicating that the pinealocytes express predominantly alpha 1D L-channels. Electrophysiological studies confirmed that the pineal expressed a single population of L-channels. The L-channel currents were inhibited by two agonists that elevate cyclic AMP: the beta-adrenergic agonist isoproterenol and PACAP. Similar inhibition was observed with a cyclic AMP analogue, 8-bromo-cyclic AMP. The presence of a cyclic AMP antagonist, Rp-adenosine 3',5'-cyclic monophosphorothioate, blocked the inhibition by isoproterenol and PACAP. Norepinephrine, a mixed alpha- and beta-adrenergic agonist, also inhibited the L-channel currents, but the inhibition was smaller. The smaller inhibition by norepinephrine was secondary to the simultaneous activation of alpha- and beta-adrenergic receptors. These results indicate that (a) pinealocytes express predominantly alpha 1D L-channels, and (b) the beta-adrenergic agonist isoproterenol and PACAP inhibit the L-channel currents through elevation of cyclic AMP. However, an alpha-adrenergic-mediated mechanism also appears to be involved in the effect of norepinephrine on the L-channel currents.
在本研究中，利用逆转录（RT）-PCR分析对大鼠松果体细胞中表达的二氢吡啶敏感性L型Ca2+通道（L通道）亚基进行了表征，并采用膜片钳技术研究了肾上腺素能激动剂和垂体腺苷酸环化酶激活多肽（PACAP）对这些通道的调节作用。RT-PCR分析表明，大鼠松果体细胞表达α1D、α2b、β2和β4 Ca(2+)通道亚基的mRNA。其他α1亚基转录本要么未表达，要么表达水平极低，这表明松果体细胞主要表达α1D L通道。电生理研究证实，松果体表达单一群体的L通道。L通道电流受到两种能升高环磷酸腺苷（cAMP）的激动剂的抑制：β肾上腺素能激动剂异丙肾上腺素和PACAP。用环磷酸腺苷类似物8-溴环磷酸腺苷也观察到了类似的抑制作用。环磷酸腺苷拮抗剂Rp-腺苷3',5'-环磷硫酯的存在阻断了异丙肾上腺素和PACAP的抑制作用。去甲肾上腺素是一种α和β肾上腺素能混合激动剂，也抑制L通道电流，但抑制作用较小。去甲肾上腺素较小的抑制作用继发于α和β肾上腺素能受体的同时激活。这些结果表明：（a）松果体细胞主要表达α1D L通道；（b）β肾上腺素能激动剂异丙肾上腺素和PACAP通过升高环磷酸腺苷来抑制L通道电流。然而，α肾上腺素能介导的机制似乎也参与了去甲肾上腺素对L通道电流的影响。
