Aquaporin 4

Aquaporin 4 is found in the basolateral cell membrane of principal collecting duct cells and provide a pathway for water to exit these cells.^[1]

AQP4 is constitutively expressed.

AQP4 is expressed in astrocytes and is upregulated by direct insult to the central nervous system.^[2]

[edit] Pathology

It is the autoimmune target in Devic's disease.

^ Agre P, Nielsen S (1996). "The aquaporin family of water channels in kidney". Nephrologie 17 (7): 409–15. PMID 8987045.
^ Nagelhus EA, Mathiisen TM, Ottersen OP (2004). "Aquaporin-4 in the central nervous system: cellular and subcellular distribution and coexpression with KIR4.1". Neuroscience 129 (4): 905–13. doi:10.1016/j.neuroscience.2004.08.053. PMID 15561407.

v • d • e Membrane transport protein: ion channels

Ca²⁺: Calcium channel	Voltage-dependent calcium channel (L-type/Ca_vα(1.1, 1.2, 1.3, 1.4), N-type, P-type/Ca_vα(2.1), Q-type, R-type, T-type, α₂δ-subunits (1, 2), β-subunits (β1, β2, β3, β4), γ-subunits (γ1, γ2, γ3, γ4) Inositol triphosphate receptor • Ryanodine receptor • Cation channels of sperm • Two-pore channel

Na⁺: Sodium channel	Na_vα (1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.9, 7A) • Na_vβ (1, 2, 3, 4) • Epithelial sodium channel

K⁺: Potassium channel	Voltage-gated (K_vα (1.1, 1.2, 1.3, 1.4, 1.5, 2.1, 3.1, 3.4, 4.1, 4.2, 4.3, 6.1, 7.1, 7.2, 7.3, 7.4, 7.5, 9.3, 10.1, 11.1/hERG) • K_vβ (1, 2), Shaker gene, KCNE1) Calcium-activated (BK channel: α1, β1, β2, β3, β4; SK channel: SK1, SK2, SK3, SK4) Inward-rectifier K_ir (1.1, 2.1, 2.2, 2.3, 2.4, GIRK, 3.1, 3.2, 3.3, 3.4, 4.1, 4.2, 5.1, 6.1, 6.2, 7.1) Tandem pore domain K2P (1, 2, 3, 4, 6, 9, 15, 17)

Cl^-: Chloride channel	Cystic fibrosis transmembrane conductance regulator

Porin	Aquaporin (1, 2, 3, 4, 5, 7, 8, 9) • Voltage-dependent anion channel (1)

Cations: TRP	TRPA (1) • TRPC (1, 2, 3, 4, 4AP, 5, 6, 7) • TRPM (1, 2, 3, 4, 5, 6, 7, 8) • TRPML (Mucolipin-1) • TRPP (1, 2) • TRPV (1, 2, 3, 4, 5, 6)

Other/general	Voltage-gated ion channel • Ligand-gated ion channel • Cyclic nucleotide-gated ion channel (α1, α2, α3, β1, β3, H1, H2, H3, H4) • Stretch-activated ion channel