Osteoblast-specific CGRP receptor -expression of osteoblastic differentiation-independent non-type I CGRP receptor-

1)在人成骨细胞MG 63中，CGRP（1-100 nM）诱导瞬时Ca^<2+>峰和随后的胞浆游离Ca^<2+>浓度（[Ca^<2+]_i）缓慢增加。在大鼠成骨细胞UMR 106中未观察到第二时相。CGRP还可诱导质膜超极化。CGRP Ⅰ型受体（CGRP-R1）的拮抗剂CGRP_1可使这种作用减弱约50%<8-37>。2）CGRP诱导的细胞反应Schild图分析在MG 63细胞中，CGRP诱导的细胞反应，如cAMP产生、p38-MAPK磷酸化和CREB磷酸化，被鉴定为由同一个CGRP受体亚型介导，可能是CGRP-R1。相反，CGRP诱导的ERK去磷酸化被认为是由单个未知亚型的CGRP受体或由CGRP-R1和未知受体亚型的组合介导的。3）肾上腺髓质素、降钙素及其特异性拮抗剂对细胞内信号通路的影响除MG 63细胞外，本文还使用了人牙周膜细胞。肾上腺髓质素（ADM）和降钙素（CT）在较高浓度（1 μM）时均能模拟CGRP的作用，但其特异性拮抗剂ADM_<22-52>2和CT_3<8-32>不能明显阻断CGRP的作用。这些结果表明，我们所观察到的CGRP的作用不是由ADM受体或CT受体介导的，而是由CGRP特异性受体亚型介导的。

1) Effects of CGRP on cytoplasmic Ca^<2+> mobilization and membrane potentialIn human osteoblastic MG63 cells, CGRP (1-100 nM) induced a transient Ca^<2+> spike and a subsequent slow increment in cytoplasmic free Ca^<2+> concentrations ([Ca^<2+>]_i). The second phase was not observed in rat osteoblastic UMR106 cells. CGRP also induced plasma membrane hyperpolarization. This action was attenuated only approximately 50% by an antagonist of CGRP subtype I receptor (CGRP-R1), CGRP_<8-37>. These findings suggest that These CGRP actions are not solely mediated by known CGRP-R1 but also by other non-subtype I receptors.2) Schild plot analysis of CGRP-induced cellular responsesIn MG63 cells, the CGRP-induced cellular responses, such as cAMP production, p38-MAPK phosphorylation, and CREB phosphorylation, were identified to be mediated by the same single CGRP receptor subtype, probably CGRP-R1. In contrast, CGRP-induced ERK dephosphorylation was suggested to be mediated either by a single unknown subtype of CGRP receptor or by a combination of CGRP-R1 and a unknown receptor subtype(s).3) Effects of adrenomedullin, calcitonin, and their specific antagonists on intracellular signaling pathwaysIn addition to MG63 cells, human periodontal ligament cells were employed here. Both adrenomedullin (ADM) and calcitonin (CT) at higher concentrations (1 μM) mimicked CGRP action, but their specific antagonists, such as ADM_<22-52> and CT_<8-32>, failed to significantly block CGRP action. These findings suggest that CGRP actions we have observed are not mediated either by ADM receptor or CT receptor, but by several CGRP-specific receptor subtypes.