Brown J E, Kaupp U B, Malbon C C
J Physiol. 1984 Aug;353:523-39. doi: 10.1113/jphysiol.1984.sp015349.
Biochemical and electrophysiological measurements were made on photoreceptor cells from Limulus ventral eyes to investigate the possible role of cyclic AMP and adenylate cyclase in the visual transduction mechanism. Cyclic AMP content in a photoreceptor-enriched fraction (the end organs) of Limulus ventral eyes was approximately 15 pmol/mg protein. The cyclic AMP content was increased by bathing eyes in 1-methyl-3-isobutyl xanthine or forskolin and was increased almost 100-fold when bathed in both. Illumination did not change cyclic AMP content significantly in any of these conditions. Discrete events that can be recorded electrophysiologically occur spontaneously in darkness. An increase in the frequency of discrete events is evoked by dim illumination. The discrete events are a sign of excitation of Limulus photoreceptor cells. Drug-induced changes in the rate of occurrence of discrete events recorded electrophysiologically in darkness were not correlated with changes in cyclic AMP content. Adenylate cyclase activity measured from a small number of pooled photoreceptor clusters was stimulated by fluoride and vanadate ions, hydrolysis-resistant analogues of GTP, cholera toxin and forskolin. The Limulus enzyme is similar pharmacologically to mammalian and avian adenylate cyclases. Activation of adenylate cyclase by drugs was not correlated with changes in the rate of occurrence of discrete events recorded electrophysiologically in darkness. A heat-treated Lubrol extract of membranes from Limulus ventral eyes reconstituted the adenylate cyclase activity of membranes from S49 mouse lymphoma cyc- mutant cells which lack a functional regulatory protein. These findings suggest that Limulus ventral eye photoreceptors contain a regulatory protein that mediates the activation of adenylate cyclase by guanine nucleotides, fluoride or cholera toxin. This regulatory protein is homologous with that found in mammalian and avian adenylate cyclases. Our findings suggest that neither cyclic AMP nor adenylate cyclase activation is a necessary or obligatory component of the excitation mechanism in Limulus ventral photoreceptors.
对美洲鲎腹眼的光感受器细胞进行了生化和电生理测量，以研究环磷酸腺苷（cAMP）和腺苷酸环化酶在视觉转导机制中可能发挥的作用。美洲鲎腹眼光感受器富集部分（终器）中的cAMP含量约为15 pmol/mg蛋白质。通过将眼睛浸泡在1-甲基-3-异丁基黄嘌呤或福斯可林中，cAMP含量会增加，若同时浸泡在这两种物质中，cAMP含量几乎会增加100倍。在这些条件下，光照均未显著改变cAMP含量。离散事件在黑暗中会自发地以电生理方式记录下来。弱光照射会引起离散事件频率增加。这些离散事件是美洲鲎光感受器细胞兴奋的标志。在黑暗中通过电生理记录的离散事件发生频率的药物诱导变化与cAMP含量的变化无关。从少量合并的光感受器簇中测得的腺苷酸环化酶活性受到氟化物、钒酸盐离子、GTP的水解抗性类似物、霍乱毒素和福斯可林的刺激。美洲鲎的这种酶在药理学上与哺乳动物和鸟类的腺苷酸环化酶相似。药物对腺苷酸环化酶的激活与在黑暗中通过电生理记录的离散事件发生频率的变化无关。美洲鲎腹眼膜的经热处理的Lubrol提取物可重建缺乏功能性调节蛋白的S49小鼠淋巴瘤cyc-突变体细胞的膜腺苷酸环化酶活性。这些发现表明，美洲鲎腹眼光感受器含有一种调节蛋白，该蛋白介导鸟嘌呤核苷酸、氟化物或霍乱毒素对腺苷酸环化酶的激活。这种调节蛋白与在哺乳动物和鸟类腺苷酸环化酶中发现的调节蛋白同源。我们的发现表明，cAMP或腺苷酸环化酶的激活都不是美洲鲎腹眼光感受器兴奋机制的必要或必然组成部分。
