This magnesium-dependent enzyme catalyzes the hydrolysis of ATP coupled with the transport of the calcium. ATP + Ca(2+)(in) + H2O = ADP + Ca(2+)(out) + H(+) + phosphate Isoform 2 (long form) is expressed only in early stages of embryonic development (cysts), while isoform 1 (short form) is also found in later embryonic stages and adults. Presents an extension, a potential transmembrane domain, which may have an important functional role. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family.