Red cell cation content and volume as a function of incubation time with vanadate. (A) K⁺ content, (B) cell water, and (C) Na⁺ content in red cells incubated with 5 mM vanadate (black circles for control red cells; black squares for patient red cells) or 5 mM vanadate with 10 µM TRAM34 (gray circles for control red cells and gray squares for patient red cells). Data are in µmoles per gram of dry weight and are mean ± standard deviation. n = 3. (D) (Upper) On the scheme of the Gardos channel subunit (adapted from Morales et al²⁴  and UniProt accession O15554), the arrow shows the position of the mutated residue and the 3 boxes in green represent the domain interacting with Calmodulin: the Calmodulin is constitutively bound to the 312 to 329 segment of the channel C-terminal region (CaMBD1); the Ca2+-dependent binding of the Calmodulin to the channel involves the segment 344 to 353 (CaMBD2A) and a stretch of 13 amino acids from 360 to 373 (CaMBD2B). (Lower) Protein sequence alignment between KCNN4 and KCNN2 in the region of the CaMBD2A.