Nwoga J, Bittar E E
Department of Physiology, University of Wisconsin, Madison 53706.
Toxicol Appl Pharmacol. 1991 Apr;108(2):330-41. doi: 10.1016/0041-008x(91)90122-u.
The aim of the present work was to explore the possibility that pentachlorophenol (PCP) influences the behavior of the resting Na efflux in single muscle fibers from the barnacle, Balanus nubilus. It is shown here that PCP causes a transitory rise in the Na efflux in both unpoisoned and ouabain-poisoned fibers and that the response is dose-dependent, the minimal effective concentration in ouabain treated fibers being less than 10(-6) M. The efficacy of PCP is significantly greater than that of 2,3,4-trichlorophenol. 2,3-Dichlorophenol is ineffective. This is also the case with phenol. The magnitude of the response to PCP is a function of external pH. Lowering pHe increases the response. The response has an absolute requirement for external Ca2+ and is a sigmoidal function of external Ca2+ concentration. Since treatment of these fibers with PCP in high concentration leads to prompt contraction, experiments were designed to determine whether the observed rise in ouabain-insensitive Na efflux is due to a fall in myoplasmic pCa and whether trigger Ca2+ originates from the bathing medium. The results obtained show that prior injection of ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) or 1,2-bis(2-aminophenoxyethane-N,N,N',N'-tetraacetic acid (BAPTA) leads to a drastic reduction in the response to PCP. They also show that prior external application of verapamil or devapamil stops the response to PCP from occurring. Both Cd2+ and Co2+ are also effective but only temporarily. Last, the effects of ryanodine and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) were tested, since the former is known to block the sarcoplasmic reticulum Ca2+ release channel, and the latter to impair the action of agents known to release Ca2+ from internal depots. Both ryanodine and TMB-8 are found to reduce the response to PCP. Taken together, these observations support the hypothesis that PCP stimulates the ouabain-insensitive Na efflux by increasing the internal free Ca2+ and that the increase in internal Ca2+ is due to the entry of trigger Ca2+ from the outside via Ca2+ channels, as well as release of Ca2+ by the sarcoplasmic reticulum via its channel. They also indicate that the efficacy of PCP depends on the 5 Cl atoms present in its aromatic ring and pHe.
本研究的目的是探讨五氯苯酚（PCP）对藤壶（Balanus nubilus）单根肌纤维静息钠外流行为产生影响的可能性。结果表明，PCP可使未中毒和哇巴因中毒的纤维中的钠外流出现短暂升高，且该反应呈剂量依赖性，在哇巴因处理的纤维中，最小有效浓度小于10⁻⁶ M。PCP的效力明显高于2,3,4 - 三氯苯酚。2,3 - 二氯苯酚无效。苯酚也是如此。对PCP的反应幅度是外部pH的函数。降低细胞外pH会增强反应。该反应绝对需要细胞外Ca²⁺，并且是细胞外Ca²⁺浓度的S形函数。由于用高浓度PCP处理这些纤维会导致迅速收缩，因此设计实验来确定观察到的哇巴因不敏感钠外流增加是否是由于肌浆pCa降低以及触发Ca²⁺是否源自浴液介质。所得结果表明，预先注射乙二醇双（β - 氨基乙基醚）N,N' - 四乙酸（EGTA）或1,2 - 双（2 - 氨基苯氧基乙烷 - N,N,N',N' - 四乙酸）（BAPTA）会导致对PCP的反应大幅降低。结果还表明，预先在外部应用维拉帕米或去甲维拉帕米可阻止对PCP的反应发生。Cd²⁺和Co²⁺也有效，但只是暂时的。最后，测试了ryanodine和8 - （N,N - 二乙氨基）辛基 - 3,4,5 - 三甲氧基苯甲酸酯（TMB - 8）的作用，因为已知前者可阻断肌浆网Ca²⁺释放通道，而后者会损害已知从内部储存库释放Ca²⁺的试剂的作用。发现ryanodine和TMB - 8均可降低对PCP的反应。综上所述，这些观察结果支持以下假设：PCP通过增加细胞内游离Ca²⁺来刺激哇巴因不敏感钠外流，并且细胞内Ca²⁺的增加是由于触发Ca²⁺通过Ca²⁺通道从外部进入以及肌浆网通过其通道释放Ca²⁺所致。它们还表明PCP的效力取决于其芳香环中存在的5个Cl原子和细胞外pH。
