Fig. 5. Effect of Na⁺/Ca⁺ exchanger (NCX) inhibition on toad ventricular contractility during hypercapnic acidosis. (A) Preincubation of isolated myocytes with 1 µmol l^–1 KB-R did not modify basal contractility but completely abolished the contractile recovery from acidosis (results from four different myocytes). (B) Similar results were obtained when ventricular strips were preincubated with 20 µmol l^–1 (2-[2-[4-(4-nitro-benzyloxy)phenyl]ethyl] isothiourea methanesulphonate (KB-R) (N=5). (C) A continuous record of tension showing that KB-R reverses the contractile recovery: the addition of the Na⁺/Ca⁺ exchanger (NCX) inhibitor (20 µmol l^–1) to ventricular strips, once the recovery reached stabilization produced a fall of developed tension (DT) to the values before the recovery. (D) Overall results of these experiments (N=4). *P<0.05 vs values before hypercapnia.