Fig. 2. Concentration–response curves to sodium nitroprusside in the absence and in the presence of BaCl2(10−5M), 4-aminopyridine (10−3M), iberiotoxin (5 × 10−8M), or apamin (5 × 10−8M), obtained in rat thoracic aortas without endothelia. Data are shown as the mean ± SEM and expressed as percent of maximal relaxation induced by papaverine (3 × 10−4M; 100%= 824 ± 85 mg [n = 5] and 968 ± 62 mg [n = 5] for control rings and rings treated with BaCl2[10−5M]; 100%= 800 ± 77 mg [n = 6] and 800 ± 77 mg [n = 6] for control rings and rings treated with 4-aminopyridine; 100%= 893 ± 75 mg [n = 6] and 840 ± 70 mg [n = 6] for control rings and rings treated with iberiotoxin; 100%= 780 ± 106 mg [n = 6] and 633 ± 75 mg [n = 6] for control rings and rings treated with apamin, respectively).