Figure 4: Dependency of H+-influx on extracellular H+ concentration. (A) Original recordings of the intracellular H+ concentration and (B) simulation of the changes in intracellular H+ concentration in MCT1-expressing oocytes injected either with 50 ng of CAII (black trace) or H2O (gray trace), respectively, during application of 10 mM lactate in HEPES-buffered solution at pHo 6.0, 6.5, 7, 7.5, and 8.0, respectively. (C) Rate of rise in intracellular H+ concentration in MCT1-expressing oocytes injected either with 50 ng of CAII or H2O as induced by application of 10 mM lactate at varying extracellular pH. (D) Simulation of the rate of rise in intracellular H+ concentration in MCT1-expressing oocytes with and without CAII as induced by application of 10 mM lactate at varying extracellular pH. Simulation of CAII-injected cells is performed at two different levels of intracellular buffer capacity.