Uniporter carrier proteins work by binding to one molecule of substrate at a time and transporting it with its concentration gradient. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules. Both kinds of uniporters rely on passive transport, as they do not directly require cellular energy to function.
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 (as in the cochlea of the ear)
- 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.
- Alberts, Bruce et al. — Essential Cell Biology, 1st edition. Garland Publishing, New York: 1998.