Physiology of bile secretion

Table 1 Membrane transporters in hepatocytes

Abbreviation	Function
Basolateral membrane (sinusoidal)
NTCP/SLC10A11	Takes up BAs
OATP/SLC21A1	Takes up BAs and OA- and exports BAs, GSH, HCO3-
MRP3/ABCC3	Export OA- conjugates, GSH
MRP4/ABCC4	Export BAs, GSH
OSTa /OSTb	Organic solute transporter: Exports BAs
NBC4c/SLC4A51	Na+-HCO3- symporter, acid extruder
NHE1/SLC9A11	Na+/H+ exchanger, acid extruder
SK2	Potassium channel, potassium efflux
SLC12A2	Na+-K+-Cl- symporter: Sodium, potassium, chloride uptake
Apical membrane (canalicular)
BSEP/ABCB111, formerly SPGE	Bile salt export pump
MRP2/ABCC21, formerly cMOAT	Export non BAs OA-, GSH
MDR1	Efflux of lipofilic cations
MDR3/ABCB4	Phospholipid flipase
ABCG5/ABCG8	Export sterols
AE2/SLC4A21	Cl-/HCO3- anion exchanger: Acid loader
Cl- channel1	Export chloride
AQP81	Water channel
NHE3/SLC9A31	Na+/H+ exchanger: Acid extruder

¹Transporters relevant to bile flow under physiological basal conditions.

Table 2 Membrane transporters in cholangiocytes: Abbreviations and function

Abbreviation	Function
Basolateral membrane
NDCBE/SLC4A81	Na+-dependent Cl-/HCO3- exchanger:
	Import HCO3- and Na+, Export H+ and Cl-
NHE/SLC91	Na+/H+ exchanger: Acid extruder
AQP41	Water channel
tASBT/SLC10A2	Export BAs and Na+
SK2	Potassium channel, potassium efflux
SLC12A2	Import Na+-K+-2Cl-
MRP3/ABCC3	Export OA- conjugates, GSH
MRP4/ABCC4	Export BAs, GSH
Apical membrane
AE2/SLC4A21	Cl-/HCO3- anion exchanger: Acid loader
CFTR1	Cl- channel: Export chloride
AQP11	Water channel
NBCe/NBC4/SLC4A5	Na+-HCO3- symporter: Acid extruder
ASBT/SLC10A2	BAs-Na+, symport: Uptake of BAs and Na+

¹Transporters relevant to bile flow under physiological basal conditions.