Why is Clo in the denominator of the GHK equation when Nao and Ko are in the numerator?

Name: Problem 3, Chapter 3: Quantitative Human Physiology
Uploaded: 2021-10-30T06:51:58-08:00
Duration: 3 min 25 s
Channel: Rabia Bibi
Description: Why is Clo in the denominator of the GHK equation when Nao and Ko are in the numerator?

step 1 So then let's discuss the design question. Why sodium ion? Sodium is smaller than sodium. And so

Why is Clo in the denominator of the GHK equation when Nao...

Key Concepts

Goldman-Hodgkin-Katz Equation

The GHK equation is used to calculate the membrane potential by taking into account the permeability and concentration gradients of multiple ions across a membrane. It integrates both the ionic permeabilities and the distribution of ions across the membrane, providing a more accurate representation than a simple Nernst equation when several ions contribute to the potential. The equation uses a weighted logarithmic mean of concentration ratios, with the specific placement of an ion's concentration (in the numerator or denominator) determined by its charge and the associated direction of the electrochemical driving force.

Ion Charge and Sign Conventions

The charge of an ion is crucial in determining its contribution to the membrane potential. For positively charged ions (cations), the ratio of external to internal concentration is used in the numerator, reflecting that a higher external concentration drives the influx of positive charge. Conversely, for negatively charged ions (anions) such as chloride, the ratio is inverted—with the external concentration appearing in the denominator—because the movement of negative charge has an opposite effect on the potential. This inversion accounts for the fact that anions moving into the cell make the inside less negative (or more positive), which is mathematically represented by flipping the concentration ratio in the logarithmic function.

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