Biological Sciences 300/301, Smith College | Neurophysiology

Case 2: Why do red blood cells need pumps?

PART A

Mature red cells lack mitochondria and RNA, and the Krebs cycle is inactive. These cells are incapable of hemoglobin synthesis. Energy is derived from glucose via the Emden-Meyerhof pathway and the hexose monophosphate shunt. Survival of red cells within the circulation depends upon the persistence of energy producing metabolic processes. These are necessary to maintain cationic gradients across the red cell membrane. By means of an active transport mechanism that depends on interaction between the membrane and ATP, sodium is pumped out of the cell and potassium moves inward. When ATP is reduced, erythrocytes tend to become more spherical because of inward movement of sodium and water.

Mountcastle, Medical Physiology, 12th ed.

Table 12.1. Extracellular and Intracellular Ion Concentrations

Concentration (mM)

Ion

Intracellular

Extracellular


Mammalian cell (eg, erythrocyte)

K+

140

5

Na+

5-15

145

Cl-

4

110

Ca2+

0.0001

2.5-5

 

Squid axon

K+

400

20

Na+

50

440

Cl-

40-150

560

Ca2+

0.0001

10


Cooper: The Cell, a molecular approach, 2nd ed