SummaryThe temperature pro®le that occurs when a brass block warms up in a vacuum evaporation unit was determined. Freshly drawn human blood was concentrated by centrifugation, and the pellet was cryo®xed and cryosectioned. The cryosections were subject to different freeze-drying protocols, using a freeze-drier with a temperature-controlled stage, to determine the effect of freeze-drying time on element distribution. Spectra were collected by spot analyses at various distances across the interface between red cells and plasma. Concentrations of sodium were high and variable outside the cell and low in the cell interior, with potassium showing the reverse distribution. The number of counts under the iron peak closely followed the potassium distribution. The concentration of sodium was higher than expected at 40 nm inside the cell membrane. This was attributed to the formation of ice crystals at the interface between the cells and plasma during cryo®xation and the use of a wide probe size.
SummaryWe describe a simple procedure to prepare cultured cells in suspension to analyse elemental content at the cellular level by electron probe X-ray microanalysis. Cells cultured in suspension were deposited onto polycarbonate tissue, culture plate well inserts, centrifuged at low g, washed to remove the extracellular medium, cryo®xed and freeze-dried, and analysed in the scanning mode of a scanning electron microscope. We tested the effect of different washing solutions (150 mM ammonium acetate, 300 mM sucrose, and distilled water) on the elemental content of cultured cells in suspension. The results demonstrated that distilled water was the best washing solution to prepare cultured cells. In addition, the low Na content, high K content and high K/Na ratio of the cells indicated that this procedure, based on the centrifugation at low g followed by cryopreparation, constitutes a satisfactory method to prepare cultured cells in suspension. We also investigated the effects of different accelerating voltages on X-ray signal collection. The results showed that moderate accelerating voltages, i.e. 10±11 kV, should be used to analyse whole cells in the scanning mode of the scanning electron microscope. We show that this method of preparation makes it possible to prepare cryosections of the cultured cells, thus permitting analysis of the elemental content at the subcellular level, i.e. nucleus, cytoplasm and mitochondria, using a scanning transmission electron microscope.
There is increasing evidence that the distribution of monovalent cations in cardiac cells may be non‐uniform, particularly in the region immediately beneath the sarcolemma, and we have proposed that a build‐up of sodium in this region could be an important factor in the development of ischaemia‐reperfusion injury. Electron probe X‐ray microanalysis is ideal for the study of such changes in distribution but the application of the technique to this problem imposes severe requirements on the specimen and on the method for cryofixation. The specimen must be perfused through its vasculature so that it can be made truly ischaemic and be successfully reperfused. It is necessary to be able to cryofix the specimen without disturbance of its blood supply, electrical stimulation or temperature. It is also important to know the time in the contraction cycle when cryofixation occurs. Here we describe the design of an automated cryofixation device which can be used to cryofix a blood perfused papillary muscle preparation at predetermined time points in the contraction cycle. Preliminary data obtained from the analysis of rabbit papillary muscles subjected to varying periods of ischaemia are included as an example of the use of the cryoclamp.
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