|Year : 1980 | Volume
| Issue : 3 | Page : 135-138
Electrolyte composition in normal and cataractous lenses
AG Chandorkar, PM Bulakh, MV Albal
Department of Pharmacology, Dr. V.M. Medical College, Solapur, India
A G Chandorkar
Department of Pharmacology, Dr. V. M. Medical College, Solapur-413 003
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chandorkar A G, Bulakh P M, Albal M V. Electrolyte composition in normal and cataractous lenses. Indian J Ophthalmol 1980;28:135-8
The constituents of the lens other than water and proteins are quantitatively minor though they may be very important metabolically. As in any other tissues, sodium, potassium, calcium and magnesium are present in lens in relatively large quantities and as expected in a tissue with high percentage of intracellular space and proteins, the lens contains much potassium with a low sodium concentration. Lens chloride is highly similar to lens sodium and forms the chief cation-anion pair in the extra cellular space. It also contains low levels of calcium but is very rich in magnesium, so much so, that it is not sensitive to the level in aqueous humor or in incubation medium.
Cataract, an opacity in the lens, can develop due to denaturation of soluble lens proteins, converting them into insoluble proteins, as in cases of nuclear type of cataracts with normal wet weight, dry weight and water contents. However, in cortical type of senile cataracts with lower dry weights, decreased protein contents and an increase in lens water, with no evidence of protein insolubilisation could be given.
An increase in the lens sodium level in cataract has been known for a long time. Calcium also accumulates in the aging lens as well as in cataractous lens and is one of the important factors in maintaining normal lens membrane permeabilitv.
The study of eventual changes in cations and chloride content in lens undergoing cataractous process could be anticipated to be of some interest as possible evidence of a failure of the mechanisms which regulate lens volume and hydration. Hence, sodium, potassium, magnesium, calcium and chloride content was determined in normal lenses of goats and in human cataractous lenses obtained after intracapsular extractions. An attempt was also made to study the effect of inhibition of cation pump on the electrolyte transport by cooling and/or damaging lens membrane by freezing and thawing in normal animal lens.
| Materials and methods|| |
Fresh goat lenses removed with cataract knife by intracapsular lens extraction method from the eye balls, obtained from slaughter house, were weighed immediately and ground in chilled 10°%,, trichloroacetic acid (TCA). After centrifugation, the supernatant fluid was retained and used for electrolyte determination.
Sodium and potassium were estimated by flame photometer, while chlorides were estimated by titration method using diphenyl carbazole indicator and the result compared with that obtained with solution of known Cl-concentration in the 10% (TCA). Magnesium was estimated by calorimetric method, using titan yellow indicator and calcium by titration method using calcium thymolphthalein as an indicator as described by Varley. Cataractous lenses from human patients were also obtained by intracapsular extraction and subjected to the above procedure.
To inhibit the cation pump, the lenses were kept in the solution (having following constituents in gm/litre - Sodium chloride - 7.8, Disodium Hydrogen phosphate - 0.106, Potassium Chloride - 0.375, Ascorbic acid - 0.193, Sodium-bicarbonate - 2.520, Glucose 0.990, which is isotonic with aqueous humour and cooled for 4 hours in ice at 4°C) or frozen for 24 hours in ice and thawed out to room temperature before being ground in chilled 10% TCA.
| Results|| |
[Table - 1]. shows the values of sodium, potassium, chlorides, magnesium and calcium in normal goat lenses before and after cooling or thawing. Normal lenses contained a high concentration of potassium, low concentration of sodium, chlorides, and calcium. While after inhibition of cation pump, an increase in intralenticular sodium, calcium and chlorides and a decrease in potassium, with an increase in lens weight, lens hydration and opacification was seen.
Human cataractous lenses had a different pattern of electrolytes which further differed in the values according to the two types of cataracts [Table - 2]. Cortical cataractous lenses had a very high concentration (about 15 times) of sodium and a far lower (1/5th to 1 /6th) level of potassium as compared to the levels of these cations in normal lens. Further the chlorides and calciumion concentration also increased in these lenses. However, the nuclear cataracts, though showed a high level of sodium, did not have any significant changes in the levels of potassium or chlorides.
| Discussion|| |
The lens is a dehydrated organ which contains approximately 66% water and 33% proteins. The cortex is more hydrated than the nucleus. The hydration is maintained by an active Na+ion-water pump which resides within the membranes of the cells in the lens epithelium and each lens fibre. Entry of potassium, inositol and aminoacids in the lenses and extrusion of sodium is governed by an active transport by this pump, while calcium, chlorides, glucose and ascorbic acid enter the lens and lactic acid leaks out of the lens through passive diffusion. Further, the normal lens, which is dehydrated, has a higher level of K+ions and lower levels of Na+ions, Clions and mater than the aqueous or the vitreous.
To maintain the electrolyte and water gradient against the surrounding fluids, the lens generates chemical and electrical energy. Chemical energy is provided by a Na ion extrusion pump coupled to K+ion intake, depending upon ATP breakdown and regulated by Na-K-ATPase enzyme. In cultures, this pump depends upon metabolism (glucose concentration) and also on physico-chemical integrity of lens fibre membranes.
An increase in the lens sodium level in the cataract is known for a long time. Recently, Maraini and Torcoli have demonstrated an increase in lens sodium in cortical cataracts in early phases and its value goes on increasing significantly above that of aqueous humour level, only when chlorides too begin to accumulate within the lens. Our observations in human senile cataractous lenses are consistent with the above findings. Though we have observed only a small increase in sodium levels in nuclear cataracts compared to 15 fold increase in cortical ones, associated with no significant change in potassium levels in nuclear cataracts and 5 fold decrease in cortical ones, Andree and Heyningen did not find any difference in sodium accumulation in nuclear and cortical cataracts.
In human senile cataracts a decrease in soluble proteins and increase in insoluble proteins (Albuminoids) is well established. Increase in Ca ion concentration has been observed in both senile human cataracts and in experimental cataracts. This increased calcium ion levels in lenses may result in protein aggregation and formation of insoluble proteins. Hence, different electrolytes patterns in nuclear and cortical cataracts deserve further investigations.
The inhibition of cation pump by cooling or damaging the lens membrane by freezing and thawing causes an increase in lens hydration and opacification with accumulation of sodium. This may be due to an alternation of ionic equilibrium of the lens which may result from inhibition of active transport of sodium or from an increase of passive permeability of lens membrane to sodium.
Data on the efficacy of cation pump and permeability of lens membrane to sodium in early stages of human cataractous lenses are obviously needed before the mechanism of senile cortical opacification can be further elucidated.
| Summary|| |
Sodium, potassium, magnesium, calcium and chloride contents were determined in normal lenses of goats and in the human cataractous lenses obtained after intracapsular extraction. An attempt was also made to study the effect of inhibition of cation pump by cooling and/or damaging lens membrane by freezing and thawing in normal animal lenses. Our results indicate an increase in sodium, chloride and calcium content along with a decrease in potassium contents in later stage in experimental cataracts and in human cataractous lenses. Increase in lens hydration and opacification was also observed after cooling and freezing. The increase in sodium ion concentration and in calcium ion concentration along with an increase in lens hydration may be responsible for the lens turbidities and for later opacification. The increase in chloride ion concentration may be secondary to increase in the sodium ions so also the decrease in ionic concentration of I potassium.
| Acknowledgement|| |
The authors are thankful to the Dean, Dr. V.M. Medical College, Solapur for the facilities given to undertake this work. The supported by financial help from U.G.C., New Delhi, which is also gratefully acknowledged.
| References|| |
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[Table - 1], [Table - 2]