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?

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.

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.

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.

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.