Electrogenic sodium/bicarbonate cotransporter with a Na(+):HCO3(-) stoichiometry varying from 1:2 to 1:3. May regulate bicarbonate influx/efflux at the basolateral membrane of cells and regulate intracellular pH. May have a higher activity than isoform 1. Inhibited by stilbene derivatives and regulated by cyclic AMP. Homodimer. Interacts with CA2/carbonic anhydrase 2 and CA4/carbonic anhydrase 4 which may regulate transporter activity. Isoform 1 but not isoform 2 interacts with AHCYL1 (via PEST domain when phosphorylated); the interaction increases SLC4A4 isoform 1 activity. Interacts with AHCYL2. Specifically expressed in kidney and to a lower extent in liver, lung, spleen, brain, skeletal muscle and heart. In kidney, expressed in proximal tubules at the corticomedullary junction. Isoform 2 is specifically expressed in kidney. Isoform 1 is expressed in kidney and pancreas while isoform 3 is specifically expressed in brain (at protein level). In brain, isoform 1 is expressed in astrocytes while isoform 3 is expressed in neurons (at protein level). In the eye, isoform 1 is expressed in cornea, conjunctiva, lens epithelium, ciliary bodies and retina while isoform 2 is detected only in the conjunctiva. Expression is first detected at E17 in spinal cord and starts in forebrain at birth. Higher expression in brain is detected at postnatal day 15 and persists throughout adulthood. Down-regulated after cadmium-intoxication and sodium or bicarbonate loading (at protein level). Down-regulated by HCO3[-] loading. Phosphorylation of Ser-1026 by PKA increases the binding of CA2 and changes the Na(+):HCO3(-) stoichiometry of the transporter from 3:1 to 2:1. Phosphorylated in presence of STK39 and dephosphorylated in presence of PP1 phosphatase; phosphorylation seems to inhibit SLC4A4 activity. N-glycosylation is not necessary for the transporter basic functions. Mutagenesis of Asn-33 into Gln has no effect on N-glycosylation. Belongs to the anion exchanger (TC 2.A.31) family.