Biomedical subjects

S A Hodson

Publications and source records attributed to S A Hodson.

26 records · Page 2Linked to original sources

PubMed1987

Physiological changes in the cornea of the ageing eye.

Donor human corneas were studied in vitro for the viability of their endothelia. Endothelial ionic permeability (measured by electrical conductivity) and bicarbonate pump activity (measured by short circuit current) were recorded. Paired corneas were used to monitor post-mortem deterioration times and drug therapy immediately prior to death noted, when possible, to identify any possible effect on tissue performance. Donor age was correlated with some loss of endothelial pump capability. In adults it seems that pump capability deteriorates with a half time decay of 72 years (correlation coefficient, 0.69). Typically, between 60 and 90 years, endothelial pump capability may drop from 32 mu amps.cm-2 to 22 mu amps.cm-2, although at any particular age, the natural variation is +/- 6 mu amps.cm-2. Over the same period, endothelial permeability does not deteriorate and there is a suggestion that the endothelial cells may even tighten up with ageing, thereby partially compensating for the suggested ageing diminution in metabolic pump capability. There is no obvious age threshold for endothelial deterioration. The use of paired corneas revealed a 50 per cent loss in endothelial barrier function per 4.8 days of storage, and less than 5 per cent loss of pump capability over a similar period. The eyes were stored whole in a moist chamber at 0-4 degrees C. A significant group of donor eyes had a markedly reduced pump capability which was not age related. The patients had had terminal drug treatments which included digoxin and furosemide.

Aged↗

PubMed1987

Paracellular ionic and transcellular water diffusions across rabbit corneal endothelium.

1. Corneal endothelial cell membrane electrical resistance is estimated at about 400 M omega by using intracellular micro-electrodes. 2. If all ion diffusion across the endothelium were transcellular, electrical resistance of the endothelial monolayer would be about 1300 omega cm2, as there are about 3000 cells mm-2. 3. Measured endothelial monolayer resistance is 12.7 +/- 0.8 omega cm2 (mean +/- S.E., n = 6), which indicates that about 99% of ion diffusion does not cross the transcellular pathway, but must pass through the paracellular route. Arguments are presented which suggest that the proportion may be even higher. 4. Endothelial passive ion permeabilities are about the same as corneal stromal passive ion permeabilities. 5. Stromal water diffusional permeability is about the same as stromal ion permeability, after allowance is made for free diffusion coefficients. In contrast, endothelial water diffusional permeability is so high as to be unmeasurable. 6. It is concluded that ions diffuse across the corneal endothelium through the paracellular route, and that water diffuses across the endothelium mainly through the transcellular route.

Animals↗

PubMed1987

The apparent reflexion coefficient of the leaky corneal endothelium to sodium chloride is about one in the rabbit.

1. Rabbit corneal thickness changes were measured after some of the NaCl in the bathing Ringer solution was substituted by a neutral sugar. 2. The response had three phases which could be closely modelled by three exponentials of different amplitudes and rate constants, originating from the time of the substitution. 3. The first, fastest, phase was interpreted as being driven by the pure osmotic pressure difference developed across the corneal endothelium by the difference between the removed NaCl and the added sugar in the bathing Ringer solution; the second was driven by the diffusion of NaCl out of the stroma; and the third, slowest, phase was driven by the diffusion of the added sugar into the stroma. 4. Consistent with the interpretation, only the third, slowest, phase had its rate constant dependent upon the nature of the substituting neutral sugar. 5. The amplitude of the pure osmotic phase was a linear function of the added sugar. Its amplitude was zero when an equal osmolarity of sugar was substituted for NaCl. 6. It was concluded that the reflexion coefficient of rabbit corneal endothelium to NaCl is the same as that to sucrose, raffinose and stachyose, i.e. about 1. 7. The calculated hydraulic conductivity of the endothelium plus stroma was about the same as that of stroma alone, and it was concluded that the hydraulic conductivity of corneal endothelium is large compared to corneal stroma. 8. It is proposed that most of the hydraulic flow in response to osmotic gradients passes through the cells, whereas salt diffuses through the paracellular route, resulting in an apparent reflexion coefficient of 1. 9. Thus, corneal endothelium is a 'leaky' (12 omega cm2) salt-permeable epithelium and, according to the present study, simultaneously a semi-permeable membrane. To resolve the terminology, we suggest the term 'bi-permeable' for such epithelia which have a high salt permeability but such a very high water permeability as to give apparent reflexion coefficients of 1.

Animals↗

PubMed1978