Byron K L
Loyola University Medical Center, Cardiovascular Institute, Maywood, IL 60153, USA.
Circ Res. 1996 May;78(5):813-20. doi: 10.1161/01.res.78.5.813.
[Arg8]-vasopressin (AVP) is both a potent vasoconstrictor and a mitogen for vascular smooth muscle cells. AVP binds to a single class of receptors (V1a) in the A7r5 rat aortic smooth muscle cell line (Kd approximately 2 nmol/L). Stimulation of these cells with AVP results in an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) by releasing intracellular Ca2+ stores and increasing Ca2+ influx; the EC50 for these effects is approximately 5 nmol/L. AVP has recently been reported to stimulate arachidonic acid release in primary cultures of rat aortic smooth muscle over a much lower concentration range (EC50 approximately 0.05 nmol/L). The present study examined the effects of varying concentrations of AVP on spontaneous Ca2+ spiking activity in fura 2-loaded A7r5 cells. Frequency of CA2+ spiking increased with increasing [AVP] in the range of 10 to 500 pmol/L. Higher concentrations of AVP inhibited spiking but elicited the characteristic [Ca2+]i changes ascribed to the release of Ca2+ stores and increased Ca2+ entry. The effects of both low and high concentrations of AVP were inhibited by [1-(beta-mercapto-beta,beta,-pentamethylenepropionic acid),2-0-methyltyrosine]arginine vasopressin, a selective V1a vasopressin antagonist. Nimodipine (50 nmol/L), a blocker of L-type voltage-sensitive Ca2+ channels, abolished the Ca(2+)-spiking activity without inhibiting a maximal [Ca2+]i response to AVP (1 mumol/L). AVP-stimulated Ca2+ spiking, but not release of intracellular Ca2+ stores, was also abolished by ONO-RS-082 (1 mumol/L), an inhibitor of phospholipase A2. These results suggest that occupation of a small fraction of V1a vasopressin receptors by AVP results in stimulation of phospholipase A2 and leads to increased Ca(2+)-spiking activity. This effect may be important for fine tuning of vascular tone, whereas maximal stimulation by AVP (full receptor occupancy) may be required for more vigorous or sustained vasoconstriction or mitogenesis.
[精氨酸8] - 血管加压素（AVP）既是一种强效血管收缩剂，也是血管平滑肌细胞的有丝分裂原。AVP与A7r5大鼠主动脉平滑肌细胞系中的一类单一受体（V1a）结合（解离常数约为2 nmol/L）。用AVP刺激这些细胞会通过释放细胞内钙库和增加钙内流导致细胞质游离钙浓度（[Ca2+]i）升高；这些效应的半数有效浓度（EC50）约为5 nmol/L。最近有报道称，AVP在更低的浓度范围内（EC50约为0.05 nmol/L）刺激大鼠主动脉平滑肌原代培养物中的花生四烯酸释放。本研究检测了不同浓度的AVP对用fura 2加载的A7r5细胞中自发钙峰活动的影响。在10至500 pmol/L范围内，随着[AVP]增加，Ca2+峰的频率增加。更高浓度的AVP抑制峰活动，但引发归因于钙库释放和钙内流增加的特征性[Ca2+]i变化。低浓度和高浓度AVP的效应均被[1 - （β - 巯基 - β，β - 五亚甲基丙酸），2 - O - 甲基酪氨酸]精氨酸血管加压素（一种选择性V1a血管加压素拮抗剂）抑制。尼莫地平（50 nmol/L），一种L型电压敏感性钙通道阻滞剂，消除了钙峰活动，但不抑制对AVP（1 μmol/L）的最大[Ca2+]i反应。ONO - RS - 082（1 μmol/L），一种磷脂酶A2抑制剂，也消除了AVP刺激的钙峰活动，但不影响细胞内钙库的释放。这些结果表明，AVP占据一小部分V1a血管加压素受体导致磷脂酶A2的刺激，并导致钙峰活动增加。这种效应可能对血管张力的微调很重要，而AVP的最大刺激（完全受体占据）可能是更强烈或持续的血管收缩或有丝分裂所必需的。
