<prompt> Regarding transpo of Ca across a membrane, which of the following is true?It is a passive transpoIt is a sympoMaintains a high intracellular Ca concentrationRequires hydrolysis of ATP  <response>: Calcium transpo occurs by secondary active transpo. Hence, option A is incorrect It is an antipo or counter transpo; occurring as Na Ca exchanger. Hence, option B is incorrect It is primarily aimed at maintaining a low cytosolic Ca. Thus, option C is incorrect. To maintain a low intracytoplasmic Ca, calcium is extruded out of the cell or pumped out from cytosol into the endoplasmic reticulum. Ca2 ATPase - The enzyme that transpos Ca2 out of the cytoplasm and into the sarcoplasmic reticulum of muscle cells. These are called P-type ATPases because they form a key phosphorylated intermediate. 