Determining K+ channel activation curves from K+ channel currents often requires the Goldman-Hodgkin-Katz equation

Potassium ion current in nerve membrane, I-K, has traditionally been described by I-K = g(K) (V - E-K), where g(K) is the K ion conductance, V is membrane potential and E-K is the K+ Nernst potential. This description has been unchallenged by most investigators in neuroscience since its introduction almost 60 years ago. The problem with the I-K similar to (V - E-K) proportionality is that it is inconsistent with the unequal distribution of K ions in the intra- and extracellular bathing media. Under physiological conditions the intracellular K+ concentration is significantly higher than the extracellular concentration. Consequently, the slope conductance at potentials positive to E-K cannot be the same as that for potentials negative to E-K, as the linear proportionality between I K and (V - E-K) requires. Instead I-K has a non-linear dependence on (V - E-K) which is well described by the Goldman-Hodgkin-Katz equation. The implications of this result for K+ channel gating and membrane excitability are reviewed in this report.