Red blood cells lost K and became loaded with Na when placed

Red blood cells lost K^+ and became \"loaded\" with Na^+ when placed in the appropriate bathing solution at lower temperature (4 degree C) over a three day period. When so treated, the internal ion concentrations were. K^+ = 5, Na^+ = 90 These cells were divided into two samples. Each sample was placed in a different bathing solution (A or B),and warmed to body temperature. The bathing solutions differed only in the concentrations of Na^+ and K^+. After 1 hour the ion concentrations shown below were observed. Which of the following would be the best interpretation of these data? Warming the solutions and cells increases the red blood cell membrane permeability to diffusion for both ions. Both Na^+ and K^+ are actively transported. Active transport of Na^+ in one direction requires transport of K^+ in the other. The red blood cell membrane is not permeable to diffusion of Na^+. Both 2 and 3. 2-4 are all correct.

Solution

The answer is option b, 2-4 are all correct

Na+-K+ pump is a transmembrane protein (also Known as Na-K+ ATPase) which utilizes energy derived from ATP hydrolysis to transport Na+ and K+ against their electrochemical gradients.
First, Na+ ions bind to high-affinity sites inside the cell which stimulates the hydrolysis of ATP and phosphorylation of the pump, inducing a conformational change that exposes the Na+-binding sites to the exterior of the cell. Consequently, the bound Na+ is released into the extracellular fluids.
At the same time, K+-binding sites are exposed on the cell surface. The binding of extracellular K+ to these sites
then stimulates hydrolysis of the phosphate group bound to the pump,which induces a second conformational change, exposing the K+-binding sites to the interior of the cell (cytosol) so that K+ is released inside the cell.
One cycle of pump transports three Na+ and two K+ ions across the plasma membrane at the expense of one molecule of ATP.

RBC membrane is not permeable to diffusion of Na⁺, because only small and hydrophobic (oxygen and Carbon dioxide) molecules are able to diffuse across a plasmamembrane passively.