Functions as an integral cofactor in cell pH regulation by controlling plasma membrane-type Na(+)/H(+) exchange activity. Promotes the induction of hematopoietic stem cell differentiation toward megakaryocytic lineage. Essential for the coupling of ERK cascade activation with the expression of ETS family genes in megakaryocytic differentiation. Also involved in granulocytic differentiation in a ERK-dependent manner. Inhibits the phosphatase activity of calcineurin (By similarity). Monomer (By similarity). Homodimer (By similarity). Expressed in both the nucleus and cytoplasm of the embryonic testis. Expressed in the bipotential gonad by E4.5 and expressed in both the testis and ovary by E5.5, but with expression higher in the testis. Expressed in the testis cords but also at low levels in the interstitium. In the ovary, expression is principally in the ovarian cortex, but also in the medulla. Also expressed in the embryonic brain, with expression highest in the region between the nasal placode and olfactory bulb. Also expressed in the embryonic heart and tail. Binds calcium via its EF-hands. Calcium-binding mediates a conformational change. Can also bind magnesium (By similarity). Belongs to the calcineurin regulatory subunit family. CHP subfamily.