In a lab experiment with isolated lung cells you observe a linear uptake in choline from the extracellular medium by the cells until the extracellular concentration of choline reaches 200 nM. At this concentration the curve levels off and the same rate of uptake is seen at 200 and 225 nM extracellular choline. What has happened that can explain this observation?

Question

Quizplus · Accepted Answer

The observation that the rate of choline uptake levels off at a certain concentration (200 nM) suggests that the transporters responsible for choline uptake have become saturated. This means that all available transporters are occupied, and the rate of uptake cannot increase further even if the extracellular concentration of choline increases. This is a characteristic feature of carrier-mediated transport processes, such as facilitated diffusion or active transport, where there is a maximum rate of transport that can be achieved when all transporters are fully utilized.

In a Lab Experiment with Isolated Lung Cells You Observe