The Ca2+ pumps and the Na+/Ca2+ exchangers

The Ca2+ ATPases or Ca2+ pumps transport Ca2+ ions out of the cytosol, by u sing the energy stored in ATP, The Na+/Ca2+ exchanger uses the chemical ene rgy of the Na+ gradient (the Na+ concentration is much higher outside than inside the cell) to remove Ca2+ from the cytosol, Ca2+ pumps are found in t he plasma membrane and in the endoplasmic reticulum of the cells. The pumps are probably present in the membrane of other organelles, but little exper imental information is available on this matter, The Na+/Ca2+ exchangers ar e located on the plasma membrane. A Na+/Ca2+ exchanger mas found in the mit ochondria, but very little is known on its structure and sequence. These tr ansporters control the Ca2+ concentration in the cytosol and are vital to p revent Ca2+ overload of the cells. Their activity is controlled by differen t mechanisms, that are still under investigation. A number of the possible isoforms for both types of proteins has been detected.