Optimizing Potassium Efflux Through Ion Channels

A particular cell could contain several different types of K+ channels. Suppose that the cell has [K+]0=5mM and [K+]i=120mM. Which combination would result in the fastest efflux (outward movement) of K+ through a single channel?

A. Vm=−80mV and a channel with a conductance of 20p℧

B. Vm=−40mV and a channel with a conductance of 10p℧

C. Vm=−40mV and a channel with a conductance of 20p℧

D. Vm=0mV and a channel with a conductance of 10p℧

E. Vm=0mV and a channel with a conductance of 20p℧

The combination that would result in the fastest efflux of K+ through a single channel is Option C: Vm=−40mV and a channel with a conductance of 20p℧.

The movement of potassium ions (K+) through a channel is influenced by the concentration gradient and the membrane potential (Vm). The cell's internal potassium concentration ([K+]i) is higher than the external potassium concentration ([K+]0), which creates a concentration gradient favoring K+ efflux. Additionally, the negative Vm also facilitates the outward movement of positively charged K+ ions.

Option C has Vm=−40mV, a more depolarized membrane potential compared to Option A (Vm=−80mV) and Option D (Vm=0mV). A less negative Vm favors K+ efflux by reducing the electrical driving force that opposes it.

Furthermore, Option C's channel has a conductance of 20p℧, which is higher than Option B (10p℧) and Option D (10p℧). Conductance represents the ease with which ions move through the channel. Higher conductance allows more ions to pass through the channel per unit of time.

The combination of a less negative Vm and a higher channel conductance in Option C makes it the most efficient in facilitating the outward movement (efflux) of K+ ions through a single channel.