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Biomedical subjects

C Wigham

Publications and source records attributed to C Wigham.

9 recordsLinked to original sources
PubMed1994

Regulation of the retinal interphotoreceptor matrix Na by the retinal pigment epithelium during the light response.

We examined the rabbit retinal pigment epithelium (RPE) for Na transport properties which would allow it to buffer undesirable changes in Na concentrations in the interphotoreceptor matrix (IPM) during light and dark cycles. The RPE is selectivity permeable to sodium. Open and short circuit transport studies with RPE indicate a circulating (choroid to retina and back) Na current which does not compromise the electrical integrity of the blood brain barrier but together with the Na permselectivity is of sufficient magnitude to buffer both upwards and downwards movements of IPM [Na] during light or dark responses.

Animals↗
PubMed1989

A near-zero membrane potential in transporting corneal endothelial cells of rabbit.

1. When rabbit corneal endothelial cells are impaled with 3 M-KCl-filled microelectrodes (Rt = 20-70 M omega) a stable membrane potential of -28.7 +/- 4.8 mV (mean +/- S.D., n = 400) is measured. 2. Varying the [KCl] of the filling solution causes a change in measured membrane potential; 154 mM gives typically -2 mV, 10 mM typically +37 mV. 3. Variation in membrane potential with different [KCl] cannot be ascribed to tip potential. Double-barrelled microelectrodes containing a different [KCl] in each barrel both give the same membrane potential when inserted into a cell. 4. Microelectrodes filled with a reference liquid ion exchanger (RLIE) give a membrane potential of +2 mV. 5. Impaling a cell with a double-barrelled microelectrode, one barrel containing KCl and the other RLIE, showed that the ion exchanger is not having a toxic effect on the cell and does not affect membrane potential measured by the KCl-filled barrel. 6. We suggest that microelectrodes containing non-isotonic concentrations of KCl generate a significant and artifactual change in membrane potential of corneal endothelial cells caused by the movement of excess KCl (originating from the microelectrode tip) across the plasma membrane where a liquid-junction potential is generated. 7. We further suggest that the physiological membrane potential of corneal endothelial cells is around zero. This could result from a solution of the constant field equation where: 0.9 PNa congruent to PK congruent to 3.2 PCl.

Animals↗
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↗