A uniporter is a

membrane transport protein A membrane transport protein (or simply transporter) is a membrane protein involved in the movement of ions, small molecules, and macromolecules, such as another protein, across a biological membrane. Transport proteins are integral membrane prote ...

that transports a single species of

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

( charged or uncharged) across a cell membrane. It may use either

facilitated diffusion Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmem ...

and transport along a

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

gradient or transport against one with an

active transport In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellu ...

process. Uniporters include both carriers and

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ...

s, and are referred to as facilitated transporters, suggesting movement down a concentration or electrochemical gradient. Uniporter carrier proteins work by binding to one

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

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 Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

– Regulated by the difference in voltage across the membrane # Stress – Regulated by physical

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

on the transporter (as in the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...

of the ear) #

Ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

– Regulated by the binding of a ligand to either the intracellular or extracellular side of the cell Uniporters are found in mitochondria and neurons. The uniporter in the mitochondria is responsible for calcium uptake. The calcium channels are used for cell signaling and triggering apoptosis. The calcium uniporter transports calcium across the inner mitochondrial membrane and is activated when calcium rises above a certain concentration.

Voltage-gated potassium channel Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized c ...

s are also uniporters that can be found in neurons and are essential for

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

s. This channel is activated by a voltage gradient created by sodium-potassium pumps. When the membrane reaches a certain voltage, the channels open which depolarizes the membrane which leads to the action potential being sent down the membrane.

References

* Alberts, Bruce et al. — ''Essential Cell Biology'', 1st edition. Garland Publishing, New York: 1998. {{Membrane transport Integral membrane proteins Transport phenomena

See also

References