Sodium-calcium exchanger

The sodium-calcium exchanger (often denoted Na⁺/Ca²⁺ exchanger, NCX, or exchange protein) is an antiporter membrane protein that removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium (Na⁺) by allowing Na⁺ to flow down its gradient across the plasma membrane in exchange for the countertransport of calcium ions (Ca²⁺). The NCX removes a single calcium ion in exchange for the import of three sodium ions. The exchanger exists in many different cell types and animal species. The NCX is considered one of the most important cellular mechanisms for removing Ca²⁺.

The exchanger is usually found in the plasma membranes and the mitochondria and endoplasmic reticulum of excitable cells.

Function

The Na⁺/Ca²⁺ exchanger does not bind very tightly to Ca²⁺ (has a low affinity), but it can transport the ions rapidly (has a high capacity), transporting up to five thousand Ca²⁺ ions per second. Therefore, it requires large concentrations of Ca²⁺ to be effective, but is useful for ridding the cell of large amounts of Ca²⁺ in a short time, as is needed in a neuron after an action potential. Thus, the exchanger also likely plays an important role in regaining the cell's normal calcium concentrations after an excitotoxic insult. Another, more ubiquitous transmembrane pump that exports calcium from the cell is the plasma membrane Ca²⁺ ATPase (PMCA), which has a much higher affinity but a much lower capacity. Since the PMCA is capable of effectively binding to Ca²⁺ even when its concentrations are quite low, it is better suited to the task of maintaining the very low concentrations of calcium that are normally within a cell. Therefore, the activities of the NCX and the PMCA complement each other.

Central Expressway (Dallas)

Central Expressway is a north–south highway in Dallas, Texas (USA) and surrounding areas. The best-known section is the North Central Expressway, a name for a freeway section of U.S. Highway 75 between downtown Dallas and McKinney, Texas. The southern terminus is at an intersection with "hidden" Interstate 345 (signed as Interstate 45) and Woodall Rodgers Expressway. From south of Main Street and its crossing under the Interstate 45 overhead in downtown Dallas, Central Expressway became the South Central Expressway, renamed César Chávez Boulevard on April 9, 2010.

North Central Expressway

Route description

The facility has 8 continuous general-purpose lanes from downtown Dallas to Legacy Drive in Plano except for a six-lane segment where it passes under Interstate 635 (two additional lanes are present but are only entrance ramps/exit ramps for Forest Lane and Midpark Road). For the six miles (10 km) north of downtown Dallas, the freeway lies more than 30 feet (9.1 m) below adjacent and partially cantilevered frontage roads.

NCX (disambiguation)

NCX can refer to: