Uniporter
A uniporter is a membrane transport protein that transports a single species of substrate across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process. Uniporters include both carriers and ion channels, and are referred to as facilitated transporters, suggesting movement down a concentration or electrochemical gradient.
Uniporter carrier proteins work by binding to one molecule of substrate at a time. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules.
There are several ways in which the opening of uniporter channels may be regulated:
- Voltage – Regulated by the difference in voltage across the membrane
- Stress – Regulated by physical pressure on the transporter
- Ligand – Regulated by the binding of a ligand to either the intracellular or extracellular side of the cell
Uniporters are involved in many biological processes, including action potentials in neurons. Voltage-gated sodium channels are involved in the propagation of a nerve impulse across the neuron. During transmission of the signal from one neuron to the next, calcium is transported into the presynaptic neuron by voltage-gated calcium channels. Potassium leak channels, also regulated by voltage, then help to restore the resting membrane potential after impulse transmission.
In the ear, sound waves cause the stress-regulated channels in the ear to open, sending an impulse to the vestibulocochlear nerve.
