Question

A researcher treats a solution containing animal cells with ouabain, a poisonous substance that interferes with the \(\mathrm{Na}^{+} / \mathrm{K}^{+}-\) ATPase embedded in the cell membrane, and causes the cell to lyse. Which of the following statements best explains ouabain's mechanism of action? A. Treatment with ouabain results in high levels of extracellular \(\mathrm{Ca}^{2+}\) B. Treatment with ouabain results in high levels of extracellular \(\mathrm{K}^{+}\)and \(\mathrm{Na}^{+}\) C. Treatment with ouabain increases intracellular concentrations of \(\mathrm{Na}^{+}\) D. Treatment with ouabain decreases intracellular concentrations of \(\mathrm{Na}^{+}\)

Short answer

Option C: Treatment with ouabain increases intracellular concentrations of Na+.

Step-by-step solution

Understand the function of Na+/K+-ATPase

The \(\text{Na}^{+}/\text{K}^{+}-\text{ATPase}\) pump helps maintain the electrochemical gradient in animal cells by actively transporting \(\text{Na}^{+}\) out of the cell and \(\text{K}^{+}\) into the cell, using ATP.

Effect of ouabain on Na+/K+-ATPase

Ouabain inhibits the \(\text{Na}^{+}/\text{K}^{+}-\text{ATPase}\) pump, preventing it from functioning. As a result, the active transport of \(\text{Na}^{+}\) out of the cell and \(\text{K}^{+}\) into the cell is halted.

Impact on intracellular sodium concentration

Since \(\text{Na}^{+}\) is no longer being actively pumped out of the cell, its concentration inside the cell begins to increase.

Cell lysis mechanism

The increased intracellular concentration of \(\text{Na}^{+}\) causes water to enter the cell through osmosis, leading to swelling and eventual lysis of the cell.

Choosing the correct statement

Option C (Treatment with ouabain increases intracellular concentrations of \(\text{Na}^{+}\)) correctly explains ouabain's mechanism of action.

Key concepts

Cell Membrane Transport

Cell membranes regulate what enters and exits the cell, maintaining the cell's internal environment. They do this through various transport mechanisms:

• Passive transport: Movement of molecules without energy input, like diffusion and osmosis.
• Active transport: Movement of molecules against their gradient, requiring energy from ATP.

A key player in this process is the Na+/K+-ATPase pump. It actively transports sodium (Na+) out of the cell and potassium (K+) into the cell, consuming ATP in the process. This pump is crucial for maintaining cell membrane potential and volume.

Active Transport

Active transport requires energy to move molecules against their concentration gradient. The Na+/K+-ATPase pump is a prime example of this process:

• Function: 3 Na+ ions are pumped out of the cell for every 2 K+ ions pumped in.
• Energy: Uses ATP to drive these movements.

This maintains low Na+ and high K+ concentrations inside the cell, creating an electrochemical gradient necessary for numerous cell functions—like nerve impulse transmission and muscle contraction. Inhibiting this pump (as ouabain does) disrupts these processes.

Cell Lysis

Cell lysis refers to the breaking down of a cell, often due to a ruptured cell membrane. In the case of Na+/K+-ATPase inhibition by ouabain:

• Sodium ions accumulate inside the cell since they are not transported out.
• This concentration gradient leads to water entering the cell by osmosis.

As water floods in, the cell swells and can eventually burst, or lyse. This bursting releases the cell’s contents into the surrounding environment, possibly damaging nearby cells. Thus, inhibiting the Na+/K+-ATPase pump can be detrimental to cell survival.

Electrochemical Gradient

An electrochemical gradient is created by the difference in charge and chemical concentration across a cell membrane. The Na+/K+-ATPase pump plays a critical role in maintaining this gradient:

• Electrochemical: Combines electrical potential and chemical concentration differences.
• Gradient Function: Essential for cell processes like nutrient absorption and nerve impulses.

By actively transporting Na+ and K+ ions, the pump ensures that the inside of the cell remains negatively charged compared to the outside. Interfering with this pump destroys the gradient, leading to cellular dysfunction and potential lysis, as seen with ouabain treatment.