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Biomedical subjects

S Hodson

Publications and source records attributed to S Hodson.

At least 37 records · Page 2Linked to original sources
PubMed1986

A test bed for ocular drugs.

Corneal endothelium plays a vital role in maintaining corneal transparency. We describe here a new in vitro technique for detecting acute effects of ocular drugs on corneal endothelium from animal species and post-mortem human tissue. The technique is based upon trans-endothelial electrical activity and leads as a consequence, to rapid, unambiguous, quantitative assessments of pharmacological effects upon endothelial barrier function and fluid pump activity.

Animals↗
PubMed1985

The movement of sodium across short-circuited rabbit corneal endothelium.

Unidirectional sodium and bicarbonate ion fluxes were measured under short-circuit conditions across rabbit corneal endothelium. A net flux of bicarbonate was measured, direction tears to lens, however no net flux of sodium was measured. From these experiments it seems that the inequality between electrically measured short-circuit current and net trans-endothelial bicarbonate ion flux cannot be bridged by any supposed net sodium flux.

Animals↗
PubMed1983

The permeability of rabbit and human corneal endothelium.

The fluxes of sodium, chloride and bicarbonate across endothelium plus stroma and then stroma alone were measured in the direction from lens-side to tear-side in rabbit and human corneas in vitro, in order to measure passive permeabilities. The results were used to calculate the permeability of the endothelium. Hodgkin's equation (1951) was then used to calculate the partial electrical conductivity of each ion crossing the endothelium. The summated electrical conductivities of sodium, chloride and bicarbonate were equal to 89 +/- 8% of the measured electrical conductivity, suggesting that the ions diffuse independently across the endothelium in the direction lens-side to tear-side. Stereological analysis of the intercellular spaces supports the idea that the ions permeate through this route and that the physical shape of the spaces determines almost entirely the permeability of the endothelial layer. Trans-endothelial sodium and chloride permeabilities are nearly equal, which may be explained by supposing the intercellular spaces include a cation exchanger of fixed negative charge capacity around 60 m-equiv l.-1 intercellular fluid.

Animals↗
PubMed1981

Bicarbonate and the trans-endothelial short circuit current of human cornea.

Experiments were performed in vitro, to determine the effect of bicarbonate ion concentration on human cornea endothelial potential difference, short circuit current and resistance. Decreasing the bicarbonate concentration resulted in a reversible and parallel fall in potential differences and short circuit current, whereas resistance remained unchanged. The results demonstrate that bicarbonate is a necessary component of the mechanisms that generate trans-endothelial short circuit current. Similarities between data derived from rabbit, ox and human suggest that a common underlying bicarbonate dependent mechanism is operating in these species.

Action Potentials↗
PubMed1981

The effect of bicarbonate ion concentration on trans-endothelial short circuit current in ox corneas.

Experiments were performed in vitro, to determine the effect of bicarbonate ion concentration on bovine cornea endothelial potential difference, short circuit current and resistance. Corneas were perfused with Ringer solutions containing 36, 12, 6, 3, 0 mM NaHCO3. Endothelial potential difference, short circuit current and resistance were measured at each concentration. Decreasing the bicarbonate concentration resulted in a reversible and parallel fall in potential difference and short circuit current, whereas resistance remained unchanged. The results demonstrate that bicarbonate is a necessary component of the mechanisms that generate trans-endothelial short circuit current.

Action Potentials↗
PubMed1980

Intraocular irrigating and replacement fluid.

The transparency of the rabbit cornea is regulated by an toward directed bicarbonate ion pump located in the corneal endothelium. The activity of the pump may be measured directly by measuring the electrical phenomena associated with it (current, potential, tissue resistance) or indirectly with a pachymeter or specular microscope with which one may measure fluid flows into or out of the stroma. Both methods give the same results. In human corneas we find that specular microscopy can give unreliable results (the scleral clamping phenomenon) but electrical investigations of endothelial inability are reliable and very similar in magnitude to those found in the rabbit. We have investigated the effects ov various aqeuous media on the human corneal endothelium, measuring viability with our experimental set-up, and have developed one which seems to cause no trauma to these clinically important cells.

Animals↗
PubMed1979

Intercellular spaces in chemically fixed corneal endothelia are related to solute pump activity not to solvent coupling.

1. Stereological analyses of the lateral intercellular spaces in the endothelium of rabbit corneas after chemical fixation were undertaken. 2. Immediately preceding chemical fixation the endothelia were in one of four transport modes: (a) bicarbonate pump activated and no coupled solvent flux, (b) bicarbonate pump activated and, coupled to it, a solvent flux, (c) no fluxes across the endothelia and (d) passive fluid fluxes across the endothelia. 3. In each transport mode, the intercellular spaces were measured after immersion in a series of fixatives in which the concentration of buffer (sodium cacodylate) was increased. 4. Lateral intercellular spaces were a function of buffer concentration in the fixative and activity of the bicarbonate pump. They were not a function of either solvent coupling or passive solvent flow. 5. It is concluded that the characteristic changes of lateral intercellular spaces, when transport is inhibited, do not indicate the site of local osmotic coupling.

Animals↗
PubMed1978

Local osmotic coupling to the active trans-endothelial bicarbonate flux in the rabbit cornea.

The present experiments investigate HCO3-, Cl- and fluid fluxes across partially destromalised corneas. Although there is no net flux of Cl-, there is a net flux of HCO-3 across the endothelium from stromal side to aqueous side which is accompanied by a flux of water in the same direction. Bulk phase osmosis cannot account for the initiation of the flux of fluid. Local osmotic coupling between ions and water is postulated to occur in the preparation. The exudate is hypertonic to the bathing Ringer solution.

Animals↗
PubMed1978

The ATP-dependent concentration of calcium by a Golgi apparatus-rich fraction isolated from rat liver.

Fractions rich in Golgi apparatus were isolated from female rat liver and incubated with different concentrations of MgATP and calcium. Calcium was sequestered by the fraction in the presence but not in the absence of ATP. The kinetics of the uptake process showed an exponential type accumulation to a maximum value which could be explained by a 'pumpleak' mechanism where Vmax was estimated at 6.7 nmol calcium/mg protein/min. Apparent Km for ATP was 1 mM and for calcium was 85 micron. The uptake is not inhibited in 5 mM azide, nor is it enhanced in 5 mM oxalate, suggesting that the sequestration is not caused by contamination from mitochondria or microsomes. Parallel experiments on a fraction rich in plasma membrane show at least a 10-fold reduction of activity over the Golgi apparatus-rich fraction, which is interpreted as evidence that plasma membrane contamination in the Golgi apparatus-rich fraction is not primarily responsible for the calcium sequestration activity. Morphometric analysis showed that about 85% of the recognizable membrane profiles in the fraction was associated with elements of the Golgi apparatus. Further evidence is given which suggests that at least 90% of the fraction was uniform in its ability to sequester calcium. In preliminary experiments it was not found possible to separate galactosyltransferase activity (a secific enzyme associated with the Golgi apparatus) from the calcium-sequestration mechanism. The stoichiometry of the hydrolysis of ATP associated with the uptake of calcium is the same as that shown by other isolated membrane systems.

Adenosine Triphosphate↗
PubMed1976

The bicarbonate ion pump in the endothelium which regulates the hydration of rabbit cornea.

1. Studies were made on the short-circuit current (s.c.c.) and fluid transport across rabbit corneal endothelium. 2. Normal s.c.c. of 27 muA.cm-2 is reduced to 19 muA.cm-2 in CO2-free Ringer, to 9 muA. cm-2 in HCO-3 -free Ringer and to zero in CO2 and HCO-3 -free Ringer. 3. Carbonic anhydrase inhibitors reduce s.c.c. from 27 to 19 muA.cm-2. Removal of exogenous CO2 causes no further reduction in s.c.c. 4. In CO2-free Ringer, net exogenous bicarbonate translocation is equal to s.c.c. 5. In all cases studied, net fluid transport across the endothelium in open circuit is directly proportional to s.c.c. 6. It is concluded that the endothelial 'pump' which regulates corneal hydration operates by 'pumping' bicarbonate ions into the aqueous humour. 7. Under physiological conditions, two thirds of the substrate is supplied by exogenous bicarbonate ions and one third is supplied by conversion of exogenous CO2 by intracellular carbonic anhydrase. 8. Metabolic CO2 does not participate significantly in the process, probably because it is at too low a concentration to compete effectively with exogenous CO2. 9. Electron histochemical studies suggest that carbonic anhydrase is located immediately underneath the posterior membrane of the endothelium, across which the active bicarbonate ion flux passes.

Animals↗