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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.

AQP4 is constitutively expressed.

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

Pathology

It is the autoimmune target in Devic's disease.

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, β-subunits (β1, β2, β4), γ-subunits (γ2) • Inositol triphosphate receptor • Ryanodine receptor • Cation channels of sperm • Two-pore channel
Na⁺: Sodium channel	Na_vα (1.1, 1.2, 1.4, 1.5, 1.7, 1.9) • Na_vβ (1, 3, 4) • Epithelial sodium channel
K⁺: Potassium channel	Voltage-gated (K_vα (1.1, 1.2, 1.3, 1.4, 1.5, 2.1, 4.2, 4.3, 7.1, 7.2, 7.3, 7.4, 10.1, 11.1/hERG) • K_vβ (1, 2), Shaker gene, KCNE1) • Calcium-activated (BK channel, SK channel, SK3) • Inward-rectifier K_ir (1.1, 2.1, 2.2, 2.3, 3.1, 3.2, 3.4, 4.1, 4.2, 6.1, 6.2)) • Tandem pore domain K2P (1, 2, 3, 4, 6, 9)
Cl^-: Chloride channel	Cystic fibrosis transmembrane conductance regulator
Porin	Aquaporin (1, 2, 3, 4) • 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, α3, β3, H1, H2, H4) • Stretch-activated ion channel