Schröder W, Frings D, Stieve H
Scan Electron Microsc. 1980(Pt 2):647-54, 606.
Electroretinogramms (ERG) of isolated crayfish retinas in salines differing in their Ca2+ concentration were recorded to monitor changes in the ERG induced by changes in the extracellular Ca2+ concentration. Laser microprobe mass spectroscopy and electron microscopy of (a) shock-frozen and (b) chemically fixed retinas were used to analyse the distribution of Ca in the photoreceptor cells. For quantitative analysis a new standardisation procedure using vacuum deposition onto the specimen of thin films as an internal standard was developed. For the first time stable isotopes were used in microbeam analysis allowing direct measurements of Ca transport and metabolism on the cellular level. The major portion of Ca was found in the black distal shielding pigment granules (DP) within the retinular photoreceptor cells. Untreated retinas and retinas preincubated in physiological saline (with 10 mmol/1 Ca2+) contained up to 100 mmol/1 Ca in the DP, while in DP-free places within the same cell Ca was as low as < 40 mumol/1. If the Ca-concentration of the saline was increased (decreased), a rise (fall) of Ca in the DP was observed. Careful Ca-depletion of the DP under ERG control allowed removal of estimated 60--70% of the 49Ca originally present and refilling with 44Ca. The maximum amplitude of the ERG-response decreased under these conditions to 50% in low Ca saline, but could be reestablished to some 70% in physiological saline containing 44Ca. We conclude, that in the living cell the DP acts sa a Ca store possibly regulating the intracellular and/or extracellular Ca level.
在钙离子浓度不同的盐溶液中记录分离的小龙虾视网膜的视网膜电图（ERG），以监测细胞外钙离子浓度变化引起的ERG变化。使用（a）速冻和（b）化学固定视网膜的激光微探针质谱分析和电子显微镜来分析光感受器细胞中钙的分布。为了进行定量分析，开发了一种新的标准化程序，该程序使用真空沉积在薄膜样品上作为内标。首次在微束分析中使用稳定同位素，从而能够在细胞水平上直接测量钙的运输和代谢。发现大部分钙存在于视杆光感受器细胞内的黑色远端屏蔽色素颗粒（DP）中。未处理的视网膜和在生理盐水中（含10 mmol/L Ca2+）预孵育的视网膜，其DP中的钙含量高达100 mmol/L，而在同一细胞内无DP的部位，钙含量低至<40 μmol/L。如果盐溶液的钙离子浓度升高（降低），则观察到DP中钙含量的升高（降低）。在ERG控制下小心地耗尽DP中的钙，可以去除估计原本存在的49Ca的60%-70%，并用44Ca重新填充。在这些条件下，ERG反应的最大幅度在低钙盐溶液中降至50%，但在含有44Ca的生理盐水中可恢复到约70%。我们得出结论，在活细胞中，DP起到钙库的作用，可能调节细胞内和/或细胞外的钙水平。
