solute carrier family 4 member 4; electrogenic sodium bicarbonate cotransporter 1; sodium bicarbonate cotransporter; Na+/HCO3- cotransporter (SLC4A4, kNBC1, NBC, NBC1, NBCE1)
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Introduction
Electrogenic Na+/HCO3- cotransporter with stoichiometry varying from 1:2 to 1:3. May regulate HCO3- influx/efflux at basolateral membrane of cells & regulate intracellular pH. Defects in SLC4A4 are the cause of renal tubular acidosis 2.
Function
- electrogenic Na+/bicarbonate cotransporter with stoichiometry varying from 1:2 to 1:3.
- may regulate bicarbonate influx/efflux at basolateral membrane, thus regulate intracellular pH
- interaction with carbonic anhydrase 2 & carbonic anhydrase 4 may regulate transporter activity
- inhibited by stilbene derivatives
- regulated by cyclic AMP
- phosphorylation of Ser-1026 by PKA increases the binding of carbonic anhydrase 2 & changes the Na+:HCO3- stoichiometry of the transporter from 3:1 to 2:1
- phosphorylation of Thr-49 regulates isoform 1 conductance
Structure
- N-glycosylation is not necessary for transporter basic functions
- belongs to the anion exchanger (TC 2.A.31) family
Compartment
Alternative splicing
named isoforms=4
Expression
- isoform 1 is expressed in pancreas > heart, skeletal muscle, liver, parotid salivary glands, prostate, colon, stomach, thyroid, brain & spinal cord
- corneal endothelium cells express only isoform 1 (at protein level)
- isoform 2 is specifically expressed in proximal tubules of the kidney
Pathology
- defects in SLC4A4 are the cause of renal tubular acidosis 2
- loss of interaction & stimulation by carbonic anhydrase 4 is the cause of retinitis pigmentosa 17
More general terms
- transmembrane 10 protein
- phosphoprotein
- glycoprotein
- solute carrier family 4 (SLC4, SLC4A)
- human longevity protein