Calcium exchanges in Anodonta cygnea: barriers and driving gradients

Electrical potential differences between the haemolymph and the extrapallial fluid, and between the haemolymph and the mantle cavity fluid, and ionic concentrations of calcium in the haemolymph and in extrapallial fluid were measured in vivo in Anodonta cygnea. The electrochemical potential of ionic calcium in the haemolymph is clearly above the electrochemical potential of ionic calcium in the environment and is very nearly in equilibrium with that of the extrapallial fluid. Simultaneous measurements of carbon dioxide partial pressure and pH in the extrapallial fluid showed that in this compartment ionic calcium is clearly above saturation. It is proposed that calcium deposition is regulated through the secretion of the organic matrix and by controlling the pH and the carbon dioxide partial pressure of the extrapallial fluid. An estimation of the minimum positive balance of calcium required to sustain shell growth together with the electrophysiological characterization of the mantle cavity epithelium showed that this tissue is not the route of entry of calcium into the animal.Abbreviations BW body weight - DW dry weight - E_EPF-S chemical potential difference - EPF extrapallial fluid - G_tot total conductance - I_sc short-circuit current - K_sp solubility product - MCE mantle cavity epithelium - MCF mantle cavity fluid - OME outer mantle epithelium - PCO₂ partial pressure of carbon dioxide - PVC Poly(vinyl chloride) - S shell - SEM standard error of mean - V _ic intracellular electrical potential - V _oc open-circuit voltage     

背角无齿蚌晶杆的扫描电镜观察

本文应用扫描电镜的方法,对背角无齿蚌的晶杆进行了研究。结果表明：晶杆外形似圆柱状,可分为二部分,即前端膨大的头部和其后渐细的杆状部。前者分左右两瓣,略弯曲,与杆状部形成一个锐角,表面呈“蜂窝状”,似一种膜性结构,其上吸附有大量的消化酶和粘液;后者两侧有凹槽,表面具许多凹陷小坑,多为圆形或卵圆形,大小不一,深浅不同,且排列不规则。未凹陷处也粗糙不平。晶杆的功能主要是搅拌和消化食物。同时,本文对晶杆结构与功能的关系也进行了讨论。     

Studies on a PMCA-like protein in the outer mantle epithelium of <Emphasis Type="Italic">Anodonta cygnea</Emphasis>: insights on calcium transcellular dynamics

Early studies on the outer mantle epithelium (OME) cells of the freshwater bivalve Anodonta cygnea (Linnaeus, 1758) revealed high ionic calcium concentrations by electrophysiological methods and subsequently a high tendency to reach an intracellular toxic condition. This toxicity could be neutralized by specific mechanisms in the cytosol of OME cells of A. cygnea. The present immunocytochemistry studies of OME cells by light and transmission electron microscopy (TEM) clearly showed a positive reaction of an antibody directed against the human plasma membrane Ca²⁺-ATPase 1 (PMCA-1) in the cytoplasm of OME cells. Also, western blot analysis of different fractions of OME cells with anti human PMCA-1 and C28R2 antibodies confirmed the presence of a PMCA-like protein with an unusual topographical localization and a molecular weight of only 70–80 kDa. These results lead us to speculate that this PMCA-like protein is distributed either in the plasma membrane or in the entire cytosol, where it eventually regulates intracellular calcium levels. Interestingly, the antibody reactions showed seasonal variations, being highest in OME samples prepared during summer when A. cygnea live under natural acidosis and absent in samples taken in winter conditions, which is in accordance with the seasonal variation of shell calcification rates. During winter, PMCA-1 antibody reaction was also detected in OME cells of animals kept only under experimentally induced acidosis conditions. Therefore, we assume that a functional role for this PMCA-like protein in the intracellular calcium regulation of OME cells during the mineralization of the shells of A. cygnea can be speculated.     

Identification of a V-type proton pump in the outer mantle epithelium of Anodonta cygnea

The dissected outer mantle epithelium (OME) of Anodonta cygnea, when mounted in Ussing type chambers, generated a spontaneous potential difference of 22.0±12.6 mV and, when short-circuited, a positive current (I_sc) of 30.0±11 μA/cm² towards the shell side and a conductance of 1.1±0.4 mS/cm². When in contact with the shell side, Bafilomycin A₁ and Concanamycin A, specific inhibitors of V-proton pumps, induced 90% inhibition of I_sc in 5 and 35 min, respectively. They had no effect in the current from the hemolymph side. Both drugs induced a dramatic fall in conductance from the shell side. Tributyltin oxide (TBTO) inhibited 90% of the I_sc in 3 min and induced a fall in conductance only from the shell side. Two observations suggest a direct effect on the proton pump: it was effective only from the shell side and the time course of the effect was identical to that of Bafilomicyn A₁. Dicyclohexycarbodiimide (DCCD) and N-ethylmaleimide (NEM) inhibited I_sc from both sides but very slowly and there was a delay of the effect from the hemolymph side in relation to the shell side. Taken together, the results suggest the presence of a V-type proton pump located at the apical (shell side) barrier of the OME.     

A possible evolutionary lag in the relationship between freshwater mussels and European bitterling

The coevolutionary dynamics between European bitterling Rhodeus amarus and freshwater unionid mussels, which the former parasitize by laying eggs on their gills, were tested. In a series of experiments fish preferences and mussel responses were compared in parasites and hosts of recent (Europe) and ancient (Asia) sympatry. Rhodeus amarus readily oviposited on the gills of all mussel species tested. Fish that laid their eggs on the gills of Asian Anodonta woodiana, however, suffered a dramatic reduction in reproductive success compared to fish that oviposited on the gills of European mussels: Unio pictorum , Unio tumidus , Anodonta anatina and Anodonta cygnea . This difference was the result of egg ejection behaviour by mussels rather than the unsuitability of the internal gill environment for European bitterling embryo development. The ejection response of mussels with a long sympatry with European bitterling was considerably more pronounced than that of mussels with a substantially shorter sympatry. The data support a coevolutionary arms race between bitterling and mussels and point to an evolutionary lag in the relationship between R. amarus and its European mussel hosts.     

褶纹冠蚌和背角无齿蚌对水体营养盐和浮游植物的影响

2009年5月31日-6月20日在广东省大沙河水库利用微型生态系统比较不同放养密度的褶纹冠蚌(Cristaria plicata)和背角无齿蚌(Anodonta woodiana)对水体氮、磷及浮游植物的影响,探讨两种蚌在控制南亚热带水库富营养化水体藻类水华上的可行性。实验结果表明,在褶纹冠蚌和背角无齿蚌处理组中,总氮、总磷和叶绿素a浓度显著增加,而铵氮的浓度显著下降;褶纹冠蚌和背角无齿蚌导致了浮游植物群落组成结构的改变和数量的增加,实验过程中绿藻所占的比例迅速上升。两种蚌之间没有显著的差异,只是在不同的作用强度下,时间上的响应不同。综合实验结果,褶纹冠蚌和背角无齿蚌难以有效地运用于我国华南地区水库的水质改善与富营养化控制。     

嗜水气单胞菌感染对背角无齿蚌5种免疫相关酶活力的影响

本研究以背角无齿蚌为材料,利用嗜水气单胞菌为诱导刺激物,对背角无齿蚌进行注射感染,在注射后3、6、12 、24、48h分别取血淋巴、肝胰腺,测定其超氧化物歧化酶（SOD）、酚氧化酶 (PO)、酸性磷酸酶 (ACP)、碱性磷酸酶 (AKP) 及过氧化氢酶 (CAT) 的活力,并研究各项酶活力的变化规律。结果表明：除3h肝胰腺外,实验组的SOD活力均不同程度地高于对照组;血清实验组的PO活力开始显著高于对照组,然后降低,而肝胰腺实验组的PO活力持续高于对照组;另外,与对照组相比,实验组中血淋巴与肝胰腺的ACP、AKP和CAT活力在不同的时间段虽然有所增强,但两者之间无显著差异。因此,认为SOD、PO活性可以作为背角无齿蚌免疫抗病功能指标参数,而ACP、AKP及CAT活性能否作为该参数还有待于进一步研究。     

Thermal resistance of the ciliary activity in the gills of the fresh water mussel Anodonta anatina

1. 1.|The thermal resistance of the activity of frontal cilia in the median gills of the fresh water mussel Anodonta anatina was studied.

2. 2.|The resistance acclimation appeared in 2 days in the gills of intact animals, but not in the isolated gills kept at 4, 14 and 24°C, for between 1 to 3 days.

3. 3.|Warm-acclimation increased the ACh sensitivity of the gills of intact mussels.

4. 4.|Isolation of the gills enhanced the thermal resistance.

5. 5.|ACh, choline and tetramethylammonium enhanced the thermal resistance in the isolated gills. whereas atropine and physostigmine diminished it.

6. 6.|It is concluded that in A. anatina the control if the thermal resistance is probably neural.

中华鲟养殖池背角无齿蚌和鲢鳙鱼生态修复效果比较

2009年5月31日-6月20日在广东省大沙河水库利用微型生态系统比较不同放养密度的褶纹冠蚌(Cristaria plicata)和背角无齿蚌(Anodonta woodiana)对水体氮、磷及浮游植物的影响,探讨两种蚌在控制南亚热带水库富营养化水体藻类水华上的可行性。实验结果表明,在褶纹冠蚌和背角无齿蚌处理组中,总氮、总磷和叶绿素a浓度显著增加,而铵氮的浓度显著下降;褶纹冠蚌和背角无齿蚌导致了浮游植物群落组成结构的改变和数量的增加,实验过程中绿藻所占的比例迅速上升。两种蚌之间没有显著的差异,只是在不同的作用强度下,时间上的响应不同。综合实验结果,褶纹冠蚌和背角无齿蚌难以有效地运用于我国华南地区水库的水质改善与富营养化控制。