Myers J B, Cantiello H F, Schwartz J H, Tauber A I
William B. Castle Hematology Research Laboratory, Boston City Hospital, Massachusetts.
Am J Physiol. 1990 Oct;259(4 Pt 1):C531-40. doi: 10.1152/ajpcell.1990.259.4.C531.
The ionic basis of phorbol 12-myristate 13-acetate (PMA)-stimulated membrane depolarization in the human neutrophil has not previously been established. Alterations in cation permeability are probably not directly responsible for the depolarization response, since the rate or Rb+ influx or efflux is unchanged upon PMA stimulation, and although Na+ fluxes are increased, depolarization is not changed by either the addition of ouabain or reduction of extracellular Na+ from 140 to 0 meq. Furthermore, the enhanced Na+ influx in stimulated cells is blocked by amiloride at 10(-3) M, but not by 10(-5) M, suggesting Na+ influx proceeds through the electroneutral Na(+)-H+ antiporter and is therefore not responsible for depolarization. Upon stimulation, Cl- content of PMA-stimulated neutrophils decreases without change in Na+ or K+ content, as determined by electron probe analysis. In addition, acute reduction in extracellular Cl- enhances the rate and extent of depolarization induced by PMA. This change in intracellular Cl- and effect of reduction in extracellular Cl- concentration on depolarization can best be accounted for by an enhanced efflux via an electrogenic mechanism. Thus enhanced conductive Cl- efflux can account for the observed depolarization. That Ca2+ regulates depolarization is evidenced by the dependence of depolarization on external Ca2+ (Cao2+). Depolarization is absent in Ca2(+)-depleted cells [internal Ca2+ (Cai2+) less than 15 nM] and is restored with titration of extracellular Ca2+, exhibiting a 50% effective dose (ED50) of 100 mM. Thus PMA-initiated depolarization is regulated by Ca2+, either from intra- or extracellular sources, but the Ca2(+)-dependent activity responsible for control of Cl- efflux is as yet uncharacterized.
佛波醇12 -肉豆蔻酸酯13 -乙酸酯（PMA）刺激人中性粒细胞膜去极化的离子基础此前尚未明确。阳离子通透性的改变可能并非去极化反应的直接原因，因为PMA刺激后Rb⁺流入或流出的速率未变，而且尽管Na⁺通量增加，但添加哇巴因或将细胞外Na⁺从140 meq降至0 meq时，去极化并未改变。此外，刺激细胞中增强的Na⁺流入在10⁻³ M的氨氯地平作用下被阻断，但在10⁻⁵ M时未被阻断，这表明Na⁺流入是通过电中性的Na⁺-H⁺反向转运体进行的，因此并非去极化的原因。通过电子探针分析确定，PMA刺激的中性粒细胞在刺激后Cl⁻含量降低，而Na⁺或K⁺含量不变。此外，细胞外Cl⁻的急性减少会增强PMA诱导的去极化速率和程度。细胞内Cl⁻的这种变化以及细胞外Cl⁻浓度降低对去极化的影响，最能通过一种电生机制增强的外流来解释。因此，增强的Cl⁻传导性外流可以解释观察到的去极化现象。Ca²⁺调节去极化这一点可由去极化对细胞外Ca²⁺（Caₒ²⁺）的依赖性来证明。在Ca²⁺耗尽的细胞[细胞内Ca²⁺（Caᵢ²⁺）小于15 nM]中不存在去极化，随着细胞外Ca²⁺的滴定恢复去极化，其半数有效剂量（ED₅₀）为100 mM。因此，PMA引发的去极化受细胞内或细胞外来源的Ca²⁺调节，但负责控制Cl⁻外流的Ca²⁺依赖性活性尚未明确。
