Gay J C
Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2588.
J Cell Physiol. 1993 Jul;156(1):189-97. doi: 10.1002/jcp.1041560125.
Although a weak direct stimulus of superoxide anion (O2-) production, platelet-activating factor (PAF) markedly enhances responses to chemotactic peptides (such as n-formyl-met-leu-phe, FMLP) and phorbol esters (such as phorbol myristate acetate, PMA) in human neutrophils. The mechanism of priming was explored first through inhibition of steps in the signal transduction pathway at and following PAF receptor occupation. Priming was not altered by pertussis toxin or intracellular calcium chelation, but the PAF receptor antagonist WEB 2086 and the protein kinase C (PKC) inhibitors sphinganine and staurosporine significantly inhibited the primed response. In order to study the regulation of PAF priming, the effect of PAF alone was desensitized by exposure to escalating doses of PAF prior to exposure to the secondary stimuli. The priming effect of PAF was not desensitized under these conditions. The role of PKC in desensitization was also studied. Prior exposure to PAF also desensitized the increase in membrane PKC activity evoked by a single concentration of PAF. However, when the PAF response was desensitized, PKC priming of the response to FMLP or PMA still occurred, suggesting that PKC activity may play a role in the maintenance of the primed state despite PAF desensitization. These data suggest that: (1) PAF priming is receptor- and PKC-mediated but is independent of pertussis toxin-inhibitable G-proteins or intracellular calcium, (2) during migration in vivo, neutrophils may be desensitized to the direct effects of PAF but maintain the capacity for enhanced responses to other stimuli, (3) desensitization of PAF-induced particulate PKC activity also occurs, but PAF primes PKC activity despite PAF desensitization, and (4) distinct mechanisms govern the direct and priming effects of PAF on oxidative metabolism.
尽管血小板活化因子（PAF）对超氧阴离子（O2-）的产生是一种微弱的直接刺激，但它能显著增强人中性粒细胞对趋化肽（如N-甲酰甲硫氨酰亮氨酰苯丙氨酸，FMLP）和佛波酯（如佛波醇肉豆蔻酸酯乙酸酯，PMA）的反应。首先通过抑制PAF受体被占据时及之后信号转导途径中的步骤来探究引发作用的机制。百日咳毒素或细胞内钙螯合并未改变引发作用，但PAF受体拮抗剂WEB 2086以及蛋白激酶C（PKC）抑制剂鞘氨醇和星形孢菌素显著抑制了引发反应。为了研究PAF引发作用的调节，在暴露于二次刺激之前，通过暴露于递增剂量的PAF使PAF单独作用的效应脱敏。在这些条件下，PAF 的引发作用并未脱敏。还研究了PKC在脱敏中的作用。预先暴露于PAF也使由单一浓度PAF引起的膜PKC活性增加脱敏。然而，当PAF反应脱敏时，对FMLP或PMA反应的PKC引发作用仍然发生，这表明尽管PAF脱敏，PKC活性可能在维持引发状态中起作用。这些数据表明：（1）PAF引发作用是由受体和PKC介导的，但独立于百日咳毒素可抑制的G蛋白或细胞内钙；（2）在体内迁移过程中，中性粒细胞可能对PAF的直接作用脱敏，但保持对其他刺激增强反应的能力；（3）PAF诱导的颗粒状PKC活性也会发生脱敏，但尽管PAF脱敏，PAF仍能引发PKC活性；（4）不同的机制支配PAF对氧化代谢的直接作用和引发作用。
