J. Vanmarle et al., CALCIUM AND ITS LOCALIZATION IN HUMAN LENS FIBERS - AN ELECTRON TOMOGRAPHIC STUDY, Experimental Eye Research, 65(1), 1997, pp. 83-88
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 reveal
ed (a) that the perimembranous precipitates as described earlier by Vr
ensen et al. (1995) are restricted to the intercellular space: no indi
cations were found of an increased intracellular submembranous calcium
level, and (b) the existence of an intracellular pool of small protei
n attached precipitates in the fibre cytoplasm not observed with conve
ntional 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 extern
al face of the fibre membrane and (b) a cytoplasmic pool of protein as
sociated calcium. Possible candidates for this cytoplasmic calcium bin
ding are discussed. (C) 1977 Academic Press Limited.