Document Detail

Colloid osmotic pressure of steer crystallins: implications for the origin of the refractive index gradient and transparency of the lens.
MedLine Citation:
PMID:  1483507     Owner:  NLM     Status:  MEDLINE    
The osmotic behavior of soluble cortical and nuclear steer lens crystallins was characterized by secondary osmometry for several ionic strength and pH conditions. Osmotic pressure versus protein concentration relationships were measured for pressures up to 1.15 x 10(6) dyn cm-2. At low concentrations (< 0.2 g ml-1), the osmotic pressure increased linearly with pressure, whereas for concentrations above 0.2 g ml-1, the pressure rose more sharply, giving progressively larger changes in osmotic pressure with increasing crystallin concentration. At a given ionic strength and applied osmotic pressure, the nuclear proteins attained a higher protein concentration than did the cortical proteins. For example, at the highest osmotic pressure of 1.15 x 10(6) dyn cm-2 at pH 7.6 and 0.1 M ionic strength, the observed protein concentrations were 0.43 g ml-1 for the cortical proteins and 0.52 g ml-1 for the nuclear proteins. For both cortical and nuclear steer crystallins, the pressure rose more steeply with concentration than do pressures for calf crystallins described in the literature. The impact of these developmental differences in osmotic pressure on lens transparency is discussed. Both the nuclear and cortical crystallins exhibited ionic strength-dependent shifts in their pressure-concentration behavior. At 0.02 M ionic strength, higher pressures were observed, whereas at 0.4 M ionic strength lower pressures were observed for a given protein concentration. The crystallins were also found to equilibrate to different protein concentrations at a constant osmotic pressure and 0.1 M ionic strength over a pH range of 4-9, with a maximum concentration around pH 5 for the cortical crystallins and pH 6 for the nuclear crystallins. Thus, the adult bovine cortical and nuclear soluble lens extracts are different in their osmotic properties, reflecting underlying differences in protein composition. The results of the ionic strength and pH experiments suggest that hard-sphere, electrostatic, and Donnan forces contribute to the total colloid osmotic pressure of the lens crystallins. However, near physiologic pH and ionic strength the charges of the proteins are screened to the extent that the colloid osmotic pressure exhibits only minor changes for large changes in ionic conditions. The differences in the osmotic behavior of the cortical and nuclear proteins are consistent with a model where regional variations in the colloid osmotic properties of the proteins across the lens help support the radial refractive index gradient that is present in vertebrate lenses. The importance of a radial concentration gradient of metabolites is also discussed.
A D Magid; A K Kenworthy; T J McIntosh
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Experimental eye research     Volume:  55     ISSN:  0014-4835     ISO Abbreviation:  Exp. Eye Res.     Publication Date:  1992 Oct 
Date Detail:
Created Date:  1993-02-17     Completed Date:  1993-02-17     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370707     Medline TA:  Exp Eye Res     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  615-27     Citation Subset:  IM    
Department of Cell Biology, Duke University Medical Center, Durham, NC 27710.
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MeSH Terms
Aging / physiology
Crystallins / chemistry*
Hydrogen-Ion Concentration
Lens Cortex, Crystalline / physiology
Lens Nucleus, Crystalline / physiology
Osmolar Concentration
Osmotic Pressure
Grant Support
Reg. No./Substance:

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