31P nuclear magnetic resonance and laser spectroscopic analyses of lens transparency during calcium-induced opacification.

The authors studied the relationships between lens phosphate metabolites and transparency in (1) normal intact calf lenses, (2) whole-lens homogenates, (3) cortical homogenates, and (4) cortical homogenates that were opacified by the addition of calcium. Transparency was measured with the use of laser spectroscopy. Phosphate metabolites and pH were measured with the use of phosphorus nuclear magnetic resonance (31P NMR) spectroscopy. 31P NMR spectra of fresh whole-lens homogenates and fresh intact lenses were nearly identical. In fresh tissue, adenosine triphosphate (ATP) accounted for 59%, 55%, and 61% of the total phosphorus detected in intact lenses, whole-lens homogenates, and cortical homogenates, respectively. As ATP decreased over time to undetectable levels, no loss of transparency was measured, indicating no relationship between ATP levels and lens opacification. In contrast, the authors found that the loss of transparency in cortical homogenates produced by additions of 5, 10, and 20 mM calcium chloride was associated with increased levels of sugar phosphates and glycerol phosphorylcholine and with decreased levels of inorganic phosphate. Loss of cortical transparency was associated with both increases or decreases in pH from the normal value.