Figure 8.

Inhibition of the ECA1 pump by vanadate and cyclopiazonic acid but not by thapsigargin. Vesicles were preincubated with each inhibitor or DMSO for 15 min at room temperature in the absence of ATP. To start the reaction, ATP was added to a mixture containing 0.1 μm free Ca²⁺ and various concentrations of sodium vanadate (A), erythrosin B (B), cyclopiazonic acid (C), or thapsigargin (D). The transport was stopped at 40 s. Control activity (100%) was 1.8 nmol Ca²⁺ mg⁻¹ protein min⁻¹. Data are the averages of three experiments. I₅₀, Inhibitor concentration for 50% displacement.