3.13 : 主动运输

Active transport is the process of moving lipid-insoluble molecules against their concentration gradient using energy and specialized transporters.

There are two main types: primary and secondary active transport.

In primary transport, the Na⁺, K⁺- ATPase pump expels three sodium ions and moves two potassium ions into cells using ATP. Drugs such as digoxin can inhibit these pumps in the heart, elevating intracellular sodium levels to mitigate heart failure.

An ABC transporter, P-glycoprotein, spends ATP transporting various drugs out of enterocytes into the GI lumen, limiting their absorption.

In secondary transport, the movement of one molecule along its concentration gradient drives the transport of another molecule against its concentration gradient. This can occur through a symport or an antiport.

In a symport, both molecules move in the same direction, whereas in an antiport, one molecule moves in, and the other moves out of the cell.