Figure 4. Multiple stimulations of Ba²⁺ (A) and Ca²⁺ (B) uptake by repeated solution applications.

A, gramicidin-treated cells expressing the Δ(241–680) NCX mutant were equilibrated in 100/40 Na/K-PSS. The labelled points designate the superfusion of 4 ml of 2 mm Ba²⁺ in 100/40 Na/K-PSS (a, b, c), 5 mm Ba²⁺ in 20/120 Na/K-PSS (d) or 0.3 mm EGTA in 20/120 Na/K-PSS (e). B, gramicidin-treated Δ(241–680) cells were equilibrated in 100/40 Na/K-PSS. Five millilitres of 100/40 Na/K-PSS containing 0.1 mm Ca²⁺ were applied by superfusion at points a, b and c. Bars beneath traces depict duration of the superfusions. This experiment was repeated, with minor variations, more than 3 times with similar results. The trace labelled ‘CHO’ represents an identical experiment carried out with non-transfected CHO T cells; the experiment with the non-transfected cells was repeated on 2 additional occasions with identical results.