An increase in extracellular K+ concentration can lead to depolarization of the plasma membrane

Question

BlackTom AI · Accepted Answer

This true/false item asks us to evaluate whether a rise in extracellular potassium concentration can cause depolarization of the plasma membrane.
Option True: A higher extracellular K+ reduces the concentration gradient for K+ across the cell membrane. Since the resting membrane potential is largely determined by the K+ gradient (via the Nernst potential for K+), diminishing this gradient makes the inside of the cell less negative relative to the outside, i.e., it leads to depolarization. In many neurons and cardiac cells, such an increase in extracellular K+ shifts the equilibrium potential for K+ toward less negative values, pulling the resting potential up closer to threshold and thereby promoting depolarization. This aligns with standard electrophysiology concepts linking external K+ to membrane potential.
Option False: If extracellular K+ were not causing depolarization, one might expect it to have no effect or to hyperpolarize. However, lowering the gradient for K+ movement outward would make the inside more positive (less negative) or counteract the usual negative resting potential, which is inconsistent with hyperpolarization. In some extreme cases, very high K+ can inactivate sodium channels after the initial depolarization, but the immediate and primary effect of increasing extracellular K+ is depolarization, not hyperpolarization. Therefore, labeling the statement as false would contradict the established relationship between extracellular K+ concentration and membrane potential.
Overall, understanding the Nernst potential for potassium and its influence on resting membrane potential clarifies why an increase in extracellular K+ tends to depolarize the cell membrane.

2261 BIOSC 1500 SEC1030 Cell Bio 1500'25 first midterm, 75 min version

An increase in extracellular K+ concentration can lead to depolarization of the plasma membrane

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