Singer-Lahat D, Rojas E, Felder C C
Laboratory of Cellular and Molecular Regulation, National Institute of Mental Health, Bethesda, MD 20892, USA.
J Membr Biol. 1997 Sep 1;159(1):21-8. doi: 10.1007/s002329900265.
Muscarinic m3 receptor-mediated changes in cytosolic Ca2+ concentration ([Ca2+]i) occur by activation of Ca2+ release channels present in the endoplasmic reticulum membrane and Ca2+ entry pathways across the plasma membrane. In this report we demonstrate the coupling of m3 muscarinic receptors to the activation of a voltage-insensitive, cation-selective channel of low conductance (3.2 +/- 0.6 pS; 25 mM Ca2+ as charge carrier) in a fibroblast cell line expressing m3 muscarinic receptor clone (A9m3 cells). Carbachol (CCh)-induced activation of the cation-selective channel occurred both in whole cell and excised membrane patches (CCh on the external side), suggesting that the underlying mechanism involves receptor-channel coupling independent of intracellular messengers. In excised inside-out membrane patches from nonstimulated A9m3 cells GTP (10 microM) and GDP (10 microM) activated cation-selective channels with conductances of approximately 4.3 and 3.3 pS, (25 mM Ca2+ as charge carrier) respectively. In contrast, ATP (10 microM), UTP (10 microM) or CTP (10 microM) failed to activate the channel. Taken together, these results suggest that carbachol and guanine nucleotides regulate the activation of a cation channel that conducts calcium.
毒蕈碱型m3受体介导的胞质Ca2+浓度（[Ca2+]i）变化是通过激活内质网膜上的Ca2+释放通道以及跨质膜的Ca2+内流途径实现的。在本报告中，我们证明了在表达m3毒蕈碱受体克隆的成纤维细胞系（A9m3细胞）中，m3毒蕈碱受体与一种低电导（3.2±0.6 pS；以25 mM Ca2+作为电荷载体）的电压不敏感、阳离子选择性通道的激活相偶联。卡巴胆碱（CCh）诱导的阳离子选择性通道激活在全细胞和切除的膜片（外侧加CCh）中均发生，这表明潜在机制涉及独立于细胞内信使的受体-通道偶联。在未刺激的A9m3细胞切除的内面向外膜片中，GTP（10 μM）和GDP（10 μM）分别激活了电导约为4.3和3.3 pS（以25 mM Ca2+作为电荷载体）的阳离子选择性通道。相比之下，ATP（10 μM）、UTP（10 μM）或CTP（10 μM）未能激活该通道。综上所述，这些结果表明卡巴胆碱和鸟嘌呤核苷酸调节传导钙的阳离子通道的激活。
