Table 1.

A schematic view of transepithelial ion transport functions through the chorionic epithelium.

Functions	Sites and mechanisms	Molecular and structural components	References
Calcium reabsorption from the eggshell	Capillary covering cells: pinocytosis model		[6, 12, 13, 15, 19, 35–38, 40, 56]
		Tight adhesion of cell membranes to shell membrane, apical vesiscles, and endocytotic-like pits	[4, 6, 15, 17, 31, 35, 36, 48, 56]
		Ca2+-binding protein	[4–6, 15, 17, 18, 37, 39, 50–52]
		Ca2+ ATPase	[10, 15, 39]
		Carbonic anhydrase	[11, 39]
	Paracellular transport	Apical tight junctions	[56]
Proton secretion for solubilization of the eggshell mineral calcite	Villus cavity cells	Carbonic anhydrase	[16, 28, 39, 52, 53, 55, 68]
		Vacuolar H+-ATPase	[21]
Bicarbonate transport for acid-base homeostasis in the embryo	Villus cavity cells
	(i) bicarbonate reabsorption from the eggshell to the embryo	AE1 anion exchanger	[30]
	(ii) HCO3− influx from the eggshell into the VC cells	Membrane-associated carbonic anhydrase	[27, 54]