Kong De-Hu, Zhou Hua, Song Jie, Ke Dao-Ping, Hu Jin-Lan, Li Zhong-Wen, Ma Rong
Laboratory of Neurophysiology, Department of Physiology, Anhui Medical University, Hefei 230032.
Sheng Li Xue Bao. 2006 Apr 25;58(2):149-56.
Contraction of smooth muscle cells is triggered by an increase in cytosolic Ca(2+) upon agonist stimulation. Ca(2+) influx across the plasma membrane constitutes a major component of the agonist-induced response in smooth muscle cells. Traditionally, voltage-operated Ca(2+) channel (VOCC) is considered as the channel mediating the Ca(2+) entry. However, this view has been challenged by recent discoveries, which demonstrated that other types of ion channels, such as store-operated and/or receptor-operated Ca(2+) channels (SOCC and/or ROCC), also participate in Ca(2+) response induced by agonists in smooth muscle cells. SOCC is defined as the channel activated in response to the depletion of the internal Ca(2+) stores, an event secondary to G protein coupled receptor or receptor tyrosine kinase stimulation. The Ca(2+) flow mediated by SOCC is termed as capacitative Ca(2+) entry (CCE). Previous study from other group has demonstrated that VOCC played a predominant role in ACh-induced contraction of distal colon smooth muscle in guinea pig. However, whether SOCC participates in the agonist-induced contractile response in this particular tissue is unknown. The present study was performed to investigate the role of CCE in ACh-induced mechanical activity of distal colon smooth muscle in rats. The contractile function of the smooth muscle was assessed by measuring isometric force of isolated rat distal colon rings. We showed that both high extracellular K(+) (40 mmol/L) and ACh (5 mumol/L) evoked striking contraction of the smooth muscle. The contractile responses were almost abolished by removal of extracellular Ca(2+) with ethylene glycol-bis(2-aminoethylether)-N,N,N',N' tetraacetic acid (EGTA), suggesting a critical contribution of extracellular source of Ca(2+) to the contraction. Verapamil (5 mumol/L), an L-type VOCC blocker, significantly attenuated, but didn't completely eliminate the high K(+)- and ACh-induced contraction (74% and 41% for high K(+) and ACh, respectively), indicating that additional channels might be involved in the contractile mechanism. Furthermore, ACh only induced transient contractions in the absence of extracellular Ca(2+). Readmission of Ca(2+) into the extracellular compartment resulted in a significant and sustained increase in the tension of the smooth muscle. This response was not affected by verapamil (5 mumol/L) and Cd(2+) (5 mumol/L), both of which efficiently block VOCC at the doses. However, La(3+), a known inhibitor of SOCC, significantly suppressed the Ca(2+) readdition-induced contraction in a dose-dependent manner. On the basis of these results, we conclude that contraction of smooth muscle in the distal colon is regulated by multiple Ca(2+) channels. In addition to VOCC-mediated Ca(2+) influx, SOCC-mediated CCE participates in agonist-induced contractile response of distal colon smooth muscle in rats.
激动剂刺激后，胞质Ca(2+)浓度升高会触发平滑肌细胞收缩。Ca(2+)跨质膜内流是平滑肌细胞激动剂诱导反应的主要组成部分。传统上，电压门控Ca(2+)通道（VOCC）被认为是介导Ca(2+)内流的通道。然而，最近的发现对这一观点提出了挑战，这些发现表明其他类型的离子通道，如储存操纵性和/或受体操纵性Ca(2+)通道（SOCC和/或ROCC），也参与了激动剂诱导的平滑肌细胞Ca(2+)反应。SOCC被定义为响应细胞内Ca(2+)储存耗竭而激活的通道，这是G蛋白偶联受体或受体酪氨酸激酶刺激后的继发事件。由SOCC介导的Ca(2+)流被称为容量性Ca(2+)内流（CCE）。其他研究小组之前的研究表明，VOCC在豚鼠远端结肠平滑肌乙酰胆碱（ACh）诱导的收缩中起主要作用。然而，在这个特定组织中，SOCC是否参与激动剂诱导的收缩反应尚不清楚。本研究旨在探讨CCE在大鼠远端结肠平滑肌ACh诱导的机械活动中的作用。通过测量离体大鼠远端结肠环的等长力来评估平滑肌的收缩功能。我们发现，高细胞外K(+)（40 mmol/L）和ACh（5 μmol/L）均可引起平滑肌显著收缩。用乙二醇双（2-氨基乙醚）-N,N,N',N' -四乙酸（EGTA）去除细胞外Ca(2+)后，收缩反应几乎完全消失，这表明细胞外Ca(2+)来源对收缩起关键作用。维拉帕米（5 μmol/L），一种L型VOCC阻滞剂，显著减弱但并未完全消除高K(+)和ACh诱导的收缩（高K(+)和ACh分别为74%和41%），这表明收缩机制可能还涉及其他通道。此外，在无细胞外Ca(2+)的情况下，ACh仅诱导短暂收缩。重新向细胞外液中加入Ca(2+)会导致平滑肌张力显著且持续增加。这种反应不受维拉帕米（5 μmol/L）和Cd(2+)（5 μmol/L）的影响，这两种药物在该剂量下均能有效阻断VOCC。然而，已知的SOCC抑制剂La(3+)以剂量依赖性方式显著抑制了Ca(2+)重新加入诱导的收缩。基于这些结果，我们得出结论，远端结肠平滑肌的收缩受多种Ca(2+)通道调节。除了VOCC介导的Ca(2+)内流外，SOCC介导的CCE也参与了大鼠远端结肠平滑肌激动剂诱导的收缩反应。
