Uniporter carrier proteins work by binding to one molecule of solute at a time and transporting it with the solute gradient. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules. Uniporters may not utilize energy other than the solute gradient. Thus they may only transport molecules with the solute gradient, and not against it.
There are several ways in which the opening of uniporter channels may be regulated:
Voltage - Regulated by the difference in voltage across the membrane