Design a brief in vitro experiment (choose the best description) to demonstrate that increasing extracellular K+ concentrations depolarizes cell membranes and increases excitability before causing inactivation of action potentials. Which experimental design is most appropriate?

• A. Replace extracellular sodium with impermeant sugars in neuronal cultures and assume that potassium effects are identical to sodium because both are cations without actually measuring membrane voltage.
• B. Use cultured excitable cells on microelectrodes, record resting membrane potential and action potentials while incrementally raising extracellular K+ concentration; observe progressive depolarization, short-term increased excitability, and eventual loss of action potentials due to sodium channel inactivation.
• C. Culture non-excitable fibroblasts and add potassium; measure collagen secretion as a proxy for membrane depolarization and extrapolate the results to neuronal excitability without recording electrical signals directly.
• D. Use isolated mitochondria and increase K+ concentration; monitor ATP production only, then infer membrane potential changes across the plasma membrane of neurons without performing any electrophysiological recordings.

Answer: (B)