Fig. 10.

I_NaL influences the contractile force frequency relationship. A: superimposed pseudo-ECGs obtained in the perfused adult LV myocardium before (KHB) and after exposure to the I_NaL enhancer ATX-II (5 nM). Arrow points to notched T wave occurring after prolonged exposure to ATX-II. B: data obtained in adult dogs are shown as mean ± SE (n = 4 muscles, 4 dogs, 4–8 yr old). *P < 0.05. Notched T waves were present in 50% of muscles exposed to ATX-II. C: examples of QT interval duration at various stimulation frequencies for LV myocardium obtained from two adult dogs (6 and 7 yr old) in KHB and after exposure to ATX-II. D: isometric contraction (top traces) and first derivative of developed tension (bottom traces) recorded at progressively higher stimulation frequencies in 1 trabecula from an adult dog before (KHB) and after exposure to ATX-II (10 nM). E: data for the effects of ATX-II on developed tension at the various frequencies of stimulation, with respect to baseline, are reported as mean ± SE (n = 3 muscles, 2 dogs, 6 and 7 yr old). *P < 0.05 vs. 333 ms; **P < 0.05 vs. 500 ms; ***P < 0.05 vs. 1,000 ms. F and G: quantitative data for developed tension (F) and developed tension normalized with respect to CL 2,000 ms (G) in adult trabeculae presented in E are shown as mean ± SE. *P < 0.05 vs. KHB; †P < 0.01 for various frequencies within the same group.