Morad Martin, Javaheri Ashkan, Risius Tim, Belmonte Steve
Department of Pharmacology, Georgetown University, Washington, DC 20057, USA.
Ann N Y Acad Sci. 2005 Jun;1047:112-21. doi: 10.1196/annals.1341.010.
It has been suggested that the multiplicity of Ca(2+) signaling pathways in atrial myocytes may contribute to the variability of its function. This article reports on a novel Ca(2+) signaling cascade initiated by mechanical forces induced by "puffing" of solution onto the myocytes. Ca(i) transients were measured in fura-2 acetoxymethyl (AM) loaded cells using alternating 340- and 410-nm excitation waves at 1.2 kHz. Pressurized puffs of bathing solutions, applied by an electronically controlled micro-barrel system, activated slowly (approximately 300 ms) developing Ca(i) transients that lasted 1,693 +/- 68 ms at room temperature. Subsequent second and third puffs, applied at approximately 20 s intervals activated significantly smaller or no Ca(i) transients. Puff-triggered Ca(i) transients could be reactivated once again following caffeine (10 mM)-induced release of Ca(2+) from sarcoplasmic reticulum (SR). Puff-triggered Ca(i) transients were independent of Ca(2+), and activation of voltage-gated Ca(2+) or cationic stretch channels or influx of Ca(2+) on Na(+)/Ca(2+)exchanger, because puffing solution containing no Ca(2+), 10 microM diltiazem, 1 mM Cd(2+), 5 mM Ni(2+), or 100 microM Gd(3+) failed to suppress them. Puff-triggered Ca(i) transients were enhanced in paced compared to quiescent myocytes. Electrically activated Ca(i) transients triggered during the time course of puff-induced transients were unaltered, suggesting functionally separate Ca(2+) pools. Contribution of inositol 1,4,5-triphosphate (IP(3))-gated or mitochondrial Ca(2+) pools or modulation of SR stores by nitric oxide/nitric oxide synthase (NO/NOS) signaling were evaluated using 0.5 to 500 microM 2-aminoethoxydiphenyl borate (2-APB) and 0.1 to 1 microM carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP), and 1 mM Nomega-Nitro-L-arginine methyl ester (L-NAME) and 7-nitroindizole, respectively. Only FCCP appeared to significantly suppress the puff-triggered Ca(i) transients. It was concluded that neither Ca(2+) influx nor depolarization was required for activation of this signaling pathway. These studies suggest that pressurized puffs of solutions activate a mechanically sensitive receptor, which signals in turn the release of Ca(2+) from a limited Ca(2+) store of mitochondria. How mechanical forces are sensed and transmitted to mitochondria to induce Ca(2+) release and what role such a Ca(2+) signaling pathway plays in the physiology or pathophysiology of the heart remain to be worked out.
有人提出，心房肌细胞中Ca(2+)信号通路的多样性可能导致其功能的变异性。本文报道了一种由溶液“吹入”心肌细胞所诱导的机械力引发的新型Ca(2+)信号级联反应。使用1.2 kHz的交替340和410 nm激发波，在负载fura-2乙酰氧基甲酯（AM）的细胞中测量Ca(i)瞬变。通过电子控制的微针管系统施加的沐浴溶液的加压吹入，缓慢激活（约300 ms）Ca(i)瞬变，在室温下持续1,693±68 ms。随后以约20 s的间隔施加的第二次和第三次吹入，激活的Ca(i)瞬变明显较小或未激活。在咖啡因（10 mM）诱导肌浆网（SR）释放Ca(2+)后，吹入触发的Ca(i)瞬变可再次被激活。吹入触发的Ca(i)瞬变与Ca(2+)无关，且与电压门控Ca(2+)或阳离子拉伸通道的激活或Ca(2+)通过Na(+)/Ca(2+)交换体的内流无关，因为不含Ca(2+)、10 μM地尔硫卓、1 mM Cd(2+)、5 mM Ni(2+)或100 μM Gd(3+)的吹入溶液未能抑制它们。与静止的心肌细胞相比，在有节奏的心肌细胞中，吹入触发的Ca(i)瞬变增强。在吹入诱导的瞬变过程中触发的电激活Ca(i)瞬变未改变，表明Ca(2+)池在功能上是分开的。使用0.5至500 μM 2-氨基乙氧基二苯硼酸（2-APB）和0.1至1 μM羰基氰-对三氟甲氧基苯腙（FCCP）以及1 mM Nω-硝基-L-精氨酸甲酯（L-NAME）和7-硝基吲唑，分别评估肌醇1,4,5-三磷酸（IP(3)）门控或线粒体Ca(2+)池或一氧化氮/一氧化氮合酶（NO/NOS）信号对SR储存的调节作用。只有FCCP似乎能显著抑制吹入触发的Ca(i)瞬变。得出的结论是，激活该信号通路既不需要Ca(2+)内流也不需要去极化。这些研究表明，溶液的加压吹入激活了一种机械敏感受体，该受体继而发出信号，促使线粒体有限的Ca(2+)储存释放Ca(2+)。机械力是如何被感知并传递到线粒体以诱导Ca(2+)释放的，以及这种Ca(2+)信号通路在心脏的生理或病理生理中起什么作用，仍有待研究。
