Ionic exchange in the corneal endothelium depends upon the metabolic rate. Which of the following can block Ionic exchange in corneal endothelium -
Ans. B - Anaerobic glycolysis activationAnaerobic glycolysis activation leads to pyruvate formation and 2 molecules of ATP.This pyruvate is further metabolized by citric acid cycle to CO2 and water and 36 molecules of ATP.But if there is hypoxia or increased anaerobic condition persisting, this pyruvate is converted to lactate by lactate dehydrogenase leading to metabolic acidosis in the aqueous.This leads to structural and functional alterations in the endothelium cells, hence interference with its ion exchange pump.Endothelium cellsThey have 2 primary functions1. Barrier function: This depends upon normal levels of calcium and glutathione. Calcium helps in maintaining the junctional complexes and glutathione protects the cornea from free radical injury helping is both barrier and metabolic function.2. Endothelial ion transport by endothelial metabolic pump:a. Na+/K+ ATPase pump: It moves sodium out of the cell, in the aqueous and potassium in the cell. In the basolateral membrane of the endothelium. It is inhibited by ouabain.b. Na+/H+ exchanger: It moves sodium into the cell and hydrogen ions outward. It is inhibited by amiloride. This acidifies the extracellular fluid, increasing the level of CO2, which in turn diffuses into the cell and converted by carbonic anhydrase inhibitor into hydrogen ion and bicarbonate. Hydrogen diffuses by Na+/H+ exchanger and bicarbonate by the cotransport.c. Na+/Bicarbonate cotransport, into the aqueous humor through the apical membrane of the cell. (Inhibited by stilbene). Aqueous humor is negative to the stroma by - 500uvolt due to this bicarbonate. This aqueous negative transendothelial potential is important for the normal functioning of endothelium. Anaerobic glycolysis leads to acidosis causing disruption of ion transport.
Inhibition of anaerobic glycolysis
Activation of anaerobic glycolysis
Activation of cAMP phosphodiesterase inhibitors
Interference with electron chain transport