Question

A researcher treats a solution containing animal cells with ouabain, a poisonous substance that interferes with the sodium–potassium ATPase embedded in the cell membrane, and the cell lyses as a result. Which of the following statements best describes ouabain’s effects? (A) \(\quad\) Treatment with ouabain results in high levels of extracellular calcium. (B) Treatment with ouabain results in high levels of extracellular potassium and sodium. (C) Treatment with ouabain increases intracellular concentrations of sodium. (D) Treatment with ouabain decreases intracellular concentrations of sodium.

Short answer

Treatment with ouabain increases intracellular concentrations of sodium.

Step-by-step solution

Understanding the Role of Sodium–Potassium ATPase

The sodium–potassium ATPase is an enzyme in the cell membrane that helps maintain the balance of sodium and potassium ions by actively transporting sodium out of the cell and potassium into the cell.

Effect of Inhibiting Sodium–Potassium ATPase

When ouabain inhibits the sodium–potassium ATPase, it prevents the enzyme from transporting sodium out of the cell and potassium into the cell. This disrupts the ion concentration gradient across the cell membrane.

Predicting Changes in Intracellular Ion Concentrations

Due to the inhibition, sodium begins to accumulate inside the cell as it is no longer being pumped out. Similarly, potassium levels inside the cell decrease because it is no longer being pumped in.

Identifying the Correct Statement

Considering these changes, the statement that best describes ouabain’s effects is: 'Treatment with ouabain increases intracellular concentrations of sodium.'

Key concepts

Ion Concentration Gradients

Ion concentration gradients are the differences in ion concentrations between the inside and the outside of the cell. This gradient is maintained by various mechanisms, including ion pumps and channels.

The sodium-potassium ATPase is an essential enzyme that actively pumps sodium ions (Na⁺) out of the cell and potassium ions (K⁺) into the cell. This active transport is vital because ions naturally move from areas of high concentration to areas of low concentration.

Maintaining these gradients is critical for various cellular functions, including electrical excitability in neurons and muscle cells. When these gradients are disrupted, it can lead to severe cellular dysfunction and even cell death.

Cell Membrane Transport

Cell membrane transport involves the movement of ions and molecules across the cell membrane.

There are multiple mechanisms for this transport:

• Passive transport, such as diffusion, where substances move along the concentration gradient without energy expenditure.
• Active transport, which requires energy (usually from ATP) to move substances against the concentration gradient.

The sodium-potassium ATPase is an example of active transport. It uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell. By doing this, it ensures that sodium and potassium stay in their respective high and low concentration areas, maintaining cellular homeostasis.

When this pump is inhibited by substances like ouabain, active transport is disrupted, compromising the cell's ability to maintain its internal environment compared to its external surroundings.

Enzyme Inhibition

Enzyme inhibition refers to the process where a molecule, known as an inhibitor, binds to an enzyme and decreases its activity.

In the context of the problem, ouabain is an inhibitor of the sodium-potassium ATPase enzyme. This inhibition means that the ATPase can no longer perform its function of pumping sodium out of the cell and potassium into the cell.

Without this active transport, the balance of these ions is thrown off, disrupting the ion concentration gradient essential for normal cell operations. The inhibition of this enzyme by ouabain ultimately leads to cellular issues and potentially cell death as seen in the exercise scenario.

Understanding enzyme inhibition is crucial for exploring numerous biochemical pathways and can offer insights into drug development and disease treatment.

Intracellular Sodium Accumulation

Intracellular sodium accumulation refers to the build-up of sodium ions inside the cell.

When the sodium-potassium ATPase is inhibited by ouabain, sodium ions are no longer pumped out of the cell. This leads to an increase in intracellular sodium levels. Simultaneously, potassium ions cannot enter the cell, adding to the imbalance.

High levels of intracellular sodium can have detrimental effects. One primary issue is cellular swelling. Sodium attracts water, causing the cell to take in more water and potentially burst, a process called lysis.

Understanding the consequences of intracellular sodium accumulation helps explain the cell's reliance on the sodium-potassium pump for survival and points to why disruptions in this enzyme can be so damaging.