The ultrastructural distribution of calcium was studied in human lens fibres with the oxalate pyroantimonate technique. In the intermediate cortex precipitates were found perimembranous and occasionally in the fibre cytoplasm. The improved resolution of electron tomography revealed (a) that the perimembranous precipitates as described earlier by Vrensen et al. (1995) are restricted to the intercellular space ; no indications were found of an increased intracellular submembranous calcium level, and (b) the existence of an intracellular pool of small protein attached precipitates in the fibre cytoplasm not observed with conventional electron microscopy. It is concluded that in the intermediate and deep cortex, where in the mature fibres all cellular calcium pools have disappeared, two calcium pools exist : (a) a pool of free calcium ionically bound to the negatively charged phospholipids of the external face of the fibre membrane and (b) a cytoplasmic pool of protein associated calcium. Possible candidates for this cytoplasmic calcium binding are discussed.
Adult human lenses with focal opacities were processed for normal as well as freeze fracture electron microscopy. Cholesterol was demonstrated using filipin cytochemistry. Filipin cytochemistry in combination with freeze fracture revealed that the amount of cholesterol in the normal fibre membranes was fully comparable with the amount of cholesterol in the deviating membranes of the focal opacities and the multilamellar bodies. As regards the cholesterol/phospholipid ratio, the deviating membranes have the same state of maturation as the surrounding normal lens fibre membranes, which implies that their synthesis is as highly coordinated as the synthesis of the normal lens fibre membranes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.