Ion transporters are linked together not physically but as

Ion transporters are “linked” together – not physically, but as a consequence of their actions. For example, a Na+-H+ antiporter and the Na+/K+ pump work together to allow a cell to raise its intracellular pH when it becomes too acidic.

(a) Try to propose a mechanism for the actions of the Na+-H+ antiporter and the Na+/K+ pump in maintaining intracellular pH.

(b) The linked action of these two transporters also causes the imbalance of both intracellular K+ concentration and the membrane potential. Please explain.

(c) How does leak K+ channel correct such imbalance?

Solution

(a) The Na+-H+ antiporter is used to stimulate the Na+/K+ pump which results in intracellular acidification, i.e the intracellular pH tilts towards acidic and this effect has been seen in the famous experiment of Bielen et al. (1990) in rabbit cardiac purkinje fibers.

(b) As Na+-H+stimulate the Na+/K+ pump an increase in the intracellular Na+ takes place. This causes charge imbalance thereby affecting the membrane potential. Generally, 3 Na+ move out of the cell and 2 K+ move into the cell and in such a combined activity this concentration gradient also gets affected.

(c) The Na+/K+ pump moves Na+ out of the cell and K+ into the cell against their concentration gradients. The leak channels allow Na+ and K+ to move across the cell membrane down their gradients. Cell membranes are considerably more permeable to K+ than to Na+ because they have many more K+ leak channels than Na+ leak channels thereby correcting the imbalance.