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 (PubMed:29500354). Interacts with CA2/carbonic anhydrase 2 and CA4/carbonic anhydrase 4 which may regulate transporter activity (PubMed:12411514, PubMed:14567693, PubMed:15218065, PubMed:15563508). Isoform 1 but not isoform 2 interacts with AHCYL1 (via PEST domain when phosphorylated); the interaction increases SLC4A4 isoform 1 activity (PubMed:16769890). Interacts with AHCYL2 (By similarity). Isoform 1 is expressed in pancreas and to a lower extent in heart, skeletal muscle, liver, parotid salivary glands, prostate, colon, stomach, thyroid, brain and spinal chord. Corneal endothelium cells express only isoform 1 (at protein level). Isoform 2 is specifically expressed in kidney at the level of proximal tubules. 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. The disease is caused by variants affecting the gene represented in this entry. Loss of interaction with and stimulation by CA4 is the cause of retinitis pigmentosa type 17 (RP17). Belongs to the anion exchanger (TC 2.A.31) family.