CalciumTransporter

Calcium transporters are a diverse group of membrane proteins that regulate the movement of Ca2+ across cellular membranes. They are essential for maintaining cytosolic Ca2+ at resting levels and for shaping rapid calcium signaling in response to stimuli.

Major families include primary active transporters that use energy from ATP hydrolysis to move Ca2+ against its gradient, secondary active transporters that exploit ion gradients generated by pumps, and channels or uniporters that mediate passive Ca2+ flux. Prominent examples are plasma membrane Ca2+-ATPases (PMCAs) and sarco/endoplasmic reticulum Ca2+-ATPases (SERCAs), which actively pump Ca2+ out of the cytosol into the extracellular space or into the sarco/endoplasmic reticulum, respectively. Na+/Ca2+ exchangers (NCXs) and H+/Ca2+ exchangers mediate Ca2+ efflux or influx by exchanging Ca2+ for Na+ or H+. The mitochondrial calcium uniporter (MCU) complex enables Ca2+ uptake into mitochondria driven by the inner membrane potential, and mitochondrial Ca2+ handling influences metabolism and apoptosis. Store-operated channels and voltage-gated calcium channels contribute to Ca2+ entry across the plasma membrane, supporting rapid signaling events; these channels are functionally linked to mobile calcium stores.

Calcium transporters are distributed across the plasma membrane and organelle membranes, including the ER, the Golgi, and mitochondria. They are tightly regulated by signaling pathways, Ca2+-binding proteins such as calmodulin, phosphorylation, and interactions with accessory subunits.

Dysregulation or mutation of calcium transporters can disrupt calcium homeostasis and is linked to conditions including cardiac arrhythmias, neurodegenerative diseases, and other conditions affecting muscle and neuronal function.