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New concepts of corneal swelling biophysics
Thursday, Sep 24, 1992 Des Iles Borromees CORNEA AND CONNECTIVE TISSUE
X ICER Abstracts
CODE: C-9
SEPTEMBER
THE ROLE OF POLYSACCHARIDES PROPERTIES
HVI’EIAiOOM:
DES ILES BORROMEES
IIME
RICHARD
A. FARRELL
1
9:Ou
The Role of Polvsaccharides D.M. Maurice (USA)
in
2
9:18
Ni%LGmcDfS of Comeal L.S. Kwok (USA)
Swclllne
3
9:36
,Yiuxlure
4
5
9%
10:12
Comeal
of Comeal Meek
and NJ.
Fullwood
Effects of Stromal Structure gattering R.L. McCally. D.E. Freund, and R.A. Farrell (USA) : Stroma J.E. Scort (UK)
&Q&Q&&In
(UK) on
University
SWELLING Medical
Cornea1 transparency is dependent upon the collagen fibrils being pushed apart by the glycosaminoglycans (GAGS) between them, and these forces are believed to manifest themselves as the stromal swelling pressure. Two GAGS, keratan sulphate and chondroitin sulphate, are predominant in the tissue but it is not known whether they both are involved in the swelling mechanism. Accordingly, the swelling pressure of normal beef stroma was compared with that of the tissue after treatment with keratanase, chondroitinase ABC, or a mixture of both enzymes. Circles of stroma, 13mm in diameter, were incubated with a small quantity of the enzyme for 24 hr and then allowed to equilibrate under a load of IOOg at 4” C. The circles were weighed at daily intervals until their mass stabilized, when they were dried and weighed again so that their hydration could be established. In other experiments the force developed by the stroma was followed by a transducer while the tissue was soaked in saline. Both methods showed a marked decrease in swelling pressure after treatment with either enzyme. Their effects were additive, as shown by a cumulative fall in pressure after treatment with the enzyme combination. Even with the combination, about 30% of the normal swelling pressure remains The structural basis for this residual component has not been determined.
(USA)
eBESENTATlON
K.M.
IN CORNEAL
Department of Ophthalmology, Stanford Center, Stanford, California, U.S.A.
BIOPHYSICAL
B
NUMBER
501
1
24tTHURSDAY
Liebl
W. Christens-Barry
I
502
2
NEW
CONCEPTS
L. Steohen Optomerry,
OF CORNEAL
SWELLING
BIOPHYSICS.
Kwok. Carneal Physiology & Biophysics Laboratory, University of Houston, Houston TX 77204-6052,
College U.S.A.
of
Collagen fib& and associated proteoglycans (PGs) in the interstitial matrix of the corneal stroma are the basis of comeal swelling, but little is known of their biophysical behaviour. The swelling kinetics of mammalian mrneal stroma in saline are well approximated by a Gibbs-Donnan equilibrium model of fixed stromal charges exerting an osmotic effect. However, prolonged swelling unmasks two thermodynamic domains in nonequilibrium swelling. This is inconsistent with a single mechanism of comeal stromal swelling. Spa&temporal trajectories indicate the presence of an attractor at a hydration Hc - 10-12 kg H2O/kg diy mass (n = lo), with higher hydrations apparently operating in the second domain. The critical region corresponds to a stromal charge Q = 1 x 10-7 mol e-. The biphasicity of extended stromal swelling can be reconciled with the Hart-Farrell model using elementary catastrophe theory, which predicts two minima in free energy. At H,,the interfbrillaty free energy barrier is associated with a critical PG chain length wth an energy barrier AE - 200-400 J. A dissipative Q (driving fluid intake) decreases in time during extended swelling, suggesting that the PGs lose some glycosaminoglycans. Pseudo-phase plots of stromal swelling analaysis further extends the Hart-Farrell model. Spatio-temporal coherence is found superimposed on stochastic fluctuations. Quasi-stable limit cycles are found in the anstimulated rabbit cornea1 stroma (“13) incubated at T = 37 oC. The spatio-temporal trajectories are centered on attractors which can be reset after mild perturbations to the corneaI stroma. Thus the molecular sidechains of the comeal PGS are elastic and can provoke structural modulation of the intertibriUary volume. Under physiological conditions the corned PGs may derive sufficient thermal energy to generate significant tissue stresses. Thermal restructuring of the interstitial microstructures appears to involve confErnational changes that decrease the stromal charge (dQ/dT < 0). (Support in part: University of Houston Research Initiation Grant 11-30962.)
503
3
STRUCTURE X~A&-R$CMN
OF CORWEAL COLL(#iEEI AND TR-
USl&#G SYNCNROTRON ELECTRON
il
si~lnufelhwhichthe the relative synthesis of p
S.148
X ICER Abstracts
CODE: C-9
SEPTEMBER
THE ROLE OF POLYSACCHARIDES PROPERTIES
HVI’EIAiOOM:
DES ILES BORROMEES
IIME
RICHARD
A. FARRELL
1
9:Ou
The Role of Polvsaccharides D.M. Maurice (USA)
in
2
9:18
Ni%LGmcDfS of Comeal L.S. Kwok (USA)
Swclllne
3
9:36
,Yiuxlure
4
5
9%
10:12
Comeal
of Comeal Meek
and NJ.
Fullwood
Effects of Stromal Structure gattering R.L. McCally. D.E. Freund, and R.A. Farrell (USA) : Stroma J.E. Scort (UK)
&Q&Q&&In
(UK) on
University
SWELLING Medical
Cornea1 transparency is dependent upon the collagen fibrils being pushed apart by the glycosaminoglycans (GAGS) between them, and these forces are believed to manifest themselves as the stromal swelling pressure. Two GAGS, keratan sulphate and chondroitin sulphate, are predominant in the tissue but it is not known whether they both are involved in the swelling mechanism. Accordingly, the swelling pressure of normal beef stroma was compared with that of the tissue after treatment with keratanase, chondroitinase ABC, or a mixture of both enzymes. Circles of stroma, 13mm in diameter, were incubated with a small quantity of the enzyme for 24 hr and then allowed to equilibrate under a load of IOOg at 4” C. The circles were weighed at daily intervals until their mass stabilized, when they were dried and weighed again so that their hydration could be established. In other experiments the force developed by the stroma was followed by a transducer while the tissue was soaked in saline. Both methods showed a marked decrease in swelling pressure after treatment with either enzyme. Their effects were additive, as shown by a cumulative fall in pressure after treatment with the enzyme combination. Even with the combination, about 30% of the normal swelling pressure remains The structural basis for this residual component has not been determined.
(USA)
eBESENTATlON
K.M.
IN CORNEAL
Department of Ophthalmology, Stanford Center, Stanford, California, U.S.A.
BIOPHYSICAL
B
NUMBER
501
1
24tTHURSDAY
Liebl
W. Christens-Barry
I
502
2
NEW
CONCEPTS
L. Steohen Optomerry,
OF CORNEAL
SWELLING
BIOPHYSICS.
Kwok. Carneal Physiology & Biophysics Laboratory, University of Houston, Houston TX 77204-6052,
College U.S.A.
of
Collagen fib& and associated proteoglycans (PGs) in the interstitial matrix of the corneal stroma are the basis of comeal swelling, but little is known of their biophysical behaviour. The swelling kinetics of mammalian mrneal stroma in saline are well approximated by a Gibbs-Donnan equilibrium model of fixed stromal charges exerting an osmotic effect. However, prolonged swelling unmasks two thermodynamic domains in nonequilibrium swelling. This is inconsistent with a single mechanism of comeal stromal swelling. Spa&temporal trajectories indicate the presence of an attractor at a hydration Hc - 10-12 kg H2O/kg diy mass (n = lo), with higher hydrations apparently operating in the second domain. The critical region corresponds to a stromal charge Q = 1 x 10-7 mol e-. The biphasicity of extended stromal swelling can be reconciled with the Hart-Farrell model using elementary catastrophe theory, which predicts two minima in free energy. At H,,the interfbrillaty free energy barrier is associated with a critical PG chain length wth an energy barrier AE - 200-400 J. A dissipative Q (driving fluid intake) decreases in time during extended swelling, suggesting that the PGs lose some glycosaminoglycans. Pseudo-phase plots of stromal swelling analaysis further extends the Hart-Farrell model. Spatio-temporal coherence is found superimposed on stochastic fluctuations. Quasi-stable limit cycles are found in the anstimulated rabbit cornea1 stroma (“13) incubated at T = 37 oC. The spatio-temporal trajectories are centered on attractors which can be reset after mild perturbations to the corneaI stroma. Thus the molecular sidechains of the comeal PGS are elastic and can provoke structural modulation of the intertibriUary volume. Under physiological conditions the corned PGs may derive sufficient thermal energy to generate significant tissue stresses. Thermal restructuring of the interstitial microstructures appears to involve confErnational changes that decrease the stromal charge (dQ/dT < 0). (Support in part: University of Houston Research Initiation Grant 11-30962.)
503
3
STRUCTURE X~A&-R$CMN
OF CORWEAL COLL(#iEEI AND TR-
USl&#G SYNCNROTRON ELECTRON
il
si~lnufelhwhichthe the relative synthesis of p
S.148