Ibarrola I, Etxeberria M, Iglesias JI, Urrutia MB, Angulo E
Departamento de Biología Animal y Genética, Facultad de Ciencias, Universidad del País Vasco/Euskal Herriko Unibertsitatea, Apartado 644, E-48080, Bilbao, Spain
J Exp Mar Biol Ecol. 2000 Sep 20;252(2):199-219. doi: 10.1016/s0022-0981(00)00235-5.
Cockles Cerastoderma edule were fed two different concentrations of two diets with different qualities which were achieved by mixing different proportions of ashed silt particles with cells of the microalgae Tetraselmis suecica. After 3 days (acute response) and 11 days (acclimated response) of exposure to the diets, we analysed the digestive activity of the digestive gland using cyto-histological and enzymatic techniques. We measured (i) the volumetric fraction of digestive and basophilic cells in digestive tubules, (ii) the diverticular radius and the thickness of digestive epithelia, (iii) the stereological parameters characterizing the lysosomal system and, (iv) dry weight, soluble protein content and specific and total amylase, cellulase, laminarinase, and protease activities of the digestive gland. In the conditions of the present study, specific cellulase and laminarinase activities in the digestive gland of cockles were correlated with the volumetric fraction of basophilic cells (r=0.672 and 0.642, respectively), whereas the specific protease was highly correlated (r=0.866) with lysosomal volume density. The implications of these correlations are discussed in relation to the feeding and absorptive parameters reported in the preceding publication. In the acute response, adjustments of the synthesis of constituents of the lysosomal/proteolytic system of the digestive cells seemed to be the only mechanism operating at the digestive level to respond to the changes in food availability. Lysosomal volume density increased with rising ingestion rate of organic matter, however, the occurrence of a limit in this short-term tissular response would account for the recorded trade-off between absorption efficiency and ingestion rate with different food qualities. With regard to acclimation, food quality determined the nature of the response of the digestive gland. With low quality diets, a time-dependent capability of the digestive gland for intensifying lysosomal/proteolytic production explains the increase of food absorption rates that result from higher filtration and ingestion rates. With high quality food, digestive acclimation differed with food particle concentration: with low rations, in spite of constant morphometrical and stereological parameters, the significant changes in the absorptive balance of biochemical components suggests the existence of an increased production of lysosomes that promotes an accelerated turn-over rate of the digestive epithelia. With high food concentrations, this response was coupled with increased activities of cellulase and laminarinase enzymes, probably as a consequence of higher rates of enzyme secretions from basophilic cells.
将鸟蛤（Cerastoderma edule）投喂两种不同质量的两种不同浓度饲料，这两种饲料通过将不同比例的灰化淤泥颗粒与微藻四爿藻（Tetraselmis suecica）细胞混合制成。在投喂饲料3天（急性反应）和11天（适应反应）后，我们使用细胞组织学和酶学技术分析消化腺的消化活动。我们测量了：（i）消化管中消化细胞和嗜碱性细胞的体积分数；（ii）盲囊半径和消化上皮厚度；（iii）表征溶酶体系统的体视学参数；以及（iv）消化腺的干重、可溶性蛋白质含量以及淀粉酶、纤维素酶、海带多糖酶和蛋白酶的比活性和总活性。在本研究条件下，鸟蛤消化腺中的纤维素酶和海带多糖酶比活性与嗜碱性细胞的体积分数相关（分别为r = 0.672和0.642），而蛋白酶比活性与溶酶体体积密度高度相关（r = 0.866）。结合前一篇出版物中报道的摄食和吸收参数，讨论了这些相关性的意义。在急性反应中，消化细胞溶酶体/蛋白水解系统成分合成的调整似乎是在消化水平上应对食物可利用性变化的唯一机制。溶酶体体积密度随有机物摄食率的增加而增加，然而，这种短期组织反应中存在的极限可以解释不同食物质量下吸收效率和摄食率之间记录到的权衡。关于适应，食物质量决定了消化腺反应的性质。对于低质量饲料，消化腺增强溶酶体/蛋白水解产物生成的时间依赖性能力解释了由于更高的滤过率和摄食率导致的食物吸收率增加。对于高质量食物，消化适应因食物颗粒浓度而异：在低定量时，尽管形态学和体视学参数恒定，但生化成分吸收平衡的显著变化表明存在溶酶体产量增加，这促进了消化上皮细胞周转率的加快。在高食物浓度下，这种反应与纤维素酶和海带多糖酶活性的增加相关，这可能是嗜碱性细胞酶分泌率更高的结果。
