Topic overview

Start with the big picture

The electrochemical potential provides a framework for predicting whether solute movement is energetically favorable: movement is spontaneous when the change in free energy is negative. Passive diffusion is non-saturable and depends on the concentration gradient, while facilitated diffusion uses channels or carriers without ATP hydrolysis. Active transport either uses ATP directly or draws on an ion gradient to move solutes against their gradients. Channels and transporters differ in their pathways and transport behavior; uniport, symport, and antiport describe how many solutes move and in which directions. The topic also introduces transporter families, electrogenic transport and membrane potential, ionophores, and vesicular movement. Together, these mechanisms help explain how membrane properties influence solute and drug movement.