The [Ca2+] sensitivity of myosin light chain phosphorylation in vascular smooth muscle is dependent on the form of stimulation. Contractile agonist stimulation, when compared to high-KCl depolarization, is associated with an increase in [Ca2+] sensitivity of phosphorylation. I evaluated potential mechanisms for this stimulus-specific response by measuring aequorin-estimated myoplasmic [Ca2+], myosin phosphorylation, and isometric stress in swine carotid media. 2. The relative [Ca2+] sensitivity of phosphorylation depended on the type of stimulus (ranked high to low sensitivity): contractile agonists (histamine, phenylephrine) = endothelin (sustained contraction) = combination of histamine and NaF greater than NaF alone = endothelin (initial contraction) = combination of histamine and depolarization = combination of NaF and depolarization greater than depolarization = Bay K 8644 = combination of depolarization and low-dose phorbol diester. 3. Activation of L-type Ca2+ channels with Bay K 8644 induced a [Ca2+] sensitivity of phosphorylation similar to depolarization, suggesting that any other effects of high KCl (such as cellular swelling) were not responsible for the low [Ca2+] sensitivity of phosphorylation. 4. The addition of either histamine or NaF (an activator of G proteins) to depolarized tissues produced similar increases in the [Ca2+] sensitivity of phosphorylation, suggesting that NaF (possibly by activation of a G protein) can mimic contractile agonist-induced increases in the [Ca2+] sensitivity of phosphorylation. 5. Phorbol dibutyrate enhanced the contractile effect of depolarization, and this enhancement was primarily caused by increases in [Ca2+] rather than an alteration in the [Ca2+] sensitivity of phosphorylation. 6. These data suggest that the [Ca2+] sensitivity of phosphorylation in smooth muscle may be regulated by agonists (possible by G protein activation); however, the role of protein kinase C activation or depolarization induced Ca2+ compartmentalization requires further study.
摘要
血管平滑肌中肌球蛋白轻链磷酸化的[Ca2+]敏感性取决于刺激形式。与高钾氯化物去极化相比，收缩性激动剂刺激与磷酸化的[Ca2+]敏感性增加有关。我通过测量猪颈动脉中层的水母发光蛋白估计的肌浆[Ca2+]、肌球蛋白磷酸化和等长张力，评估了这种刺激特异性反应的潜在机制。2. 磷酸化的相对[Ca2+]敏感性取决于刺激类型（从高到低敏感性排序）：收缩性激动剂（组胺、去氧肾上腺素）=内皮素（持续性收缩）=组胺和氟化钠的组合大于单独的氟化钠=内皮素（初始收缩）=组胺和去极化的组合=氟化钠和去极化的组合大于去极化=Bay K 8644=去极化和低剂量佛波酯的组合。3. 用Bay K 8644激活L型Ca2+通道诱导的磷酸化[Ca2+]敏感性类似于去极化，这表明高钾氯化物的任何其他作用（如细胞肿胀）都不是磷酸化的低[Ca2+]敏感性的原因。4. 向去极化组织中添加组胺或氟化钠（一种G蛋白激活剂）会使磷酸化的[Ca2+]敏感性产生类似的增加，这表明氟化钠（可能通过激活G蛋白）可以模拟收缩性激动剂诱导的磷酸化[Ca2+]敏感性增加。5. 佛波二丁酸酯增强了去极化的收缩作用，这种增强主要是由[Ca2+]增加引起的，而不是磷酸化的[Ca2+]敏感性改变。6. 这些数据表明，平滑肌中磷酸化的[Ca2+]敏感性可能受激动剂调节（可能通过G蛋白激活）；然而，蛋白激酶C激活或去极化诱导的Ca2+区室化的作用需要进一步研究。
