Figure 1. The PG domain of CAIX is involved in facilitation of MCT1/4 transport activity.

(A) Amino acid sequence of the human CAIX proteoglycan-like domain. Negatively charged amino acids are labelled in red, positively charged amino acids are labelled in blue. (B, C) Original recordings of the change in intracellular H⁺ concentration ([H⁺]_i) in oocytes expressing (B) MCT1 or (C) MCT4 (black trace), MCT1/4 + CAIX-WT (blue trace), and MCT1/4 + CAIX-ΔPG (red trace), respectively, during application of 3 and 10 mM of lactate and 5% CO₂ / 10 mM HCO₃^-. (D-I) Rate of change in intracellular H⁺ concentration (Δ[H⁺]/Δt) as induced by application (D, G) and removal (E, H) of 3 and 10 mM lactate, and application of 5% CO₂ / 10 mM HCO₃^- (F, I), respectively, in oocytes expressing MCT1/4 (gray), MCT1/4+CAIX-WT (blue), and MCT1+CAII-ΔPG (red), respectively. Data are represented as mean + SEM. Significance in differences was tested with ANOVA, followed by means comparison. The black significance indicators above the bars for MCT1/4+CAIX/CAIX-ΔPG-coexpressing oocytes refer to the values from oocytes expressing MCT1/4 alone. The blue significance indicators above the bars for MCT1/4+CAIX-ΔPG-coexpressing oocytes refer to the values from oocytes coexpressing MCT1/4 + CAIX.