The calcium pump of the plasma membrane, termed PMCA ATPase, pumps calcium from the cytosol to the extracellular space. This membrane-bound enzyme is related to a number of other ATPases including the SERCA ATPase and the sodium/K+ pump.
There are four different genes encoding PMCA ATPase and studies have revealed 20 isoforms of the pump generated by alternate splicing of the primary gene products. mRNA distribution studies show that gene products 1 and 4 are transcribed in most tissues, however, products 2 and 3 are more tissue specific. Transcription of the splicing variants has also been found to be tissue specific. In the pancreas, where insulin secretion is calcium dependent, the beta cells only express the 4b isoform, however the alpha and gamma cells express both 4a and 4b isoforms. Studies have also shown that different splice variants have different affinities for calcium and calmodulin.
ATPase, Ca++ transporting, plasma membrane 3; cilia and flagella associated protein 39; plasma membrane calcium ATPase; Plasma membrane calcium ATPase isoform 3; plasma membrane calcium pump; Plasma Membrane Calcium Pump ATPase 3; Plasma membrane calcium pump isoform 3; Plasma membrane calcium-transporting ATPase 3; PMCA3