Fig. 9.
INaL alters mechanical properties of the ventricular myocardium. A: isometric contraction (top trace) and first derivative of developed tension (bottom trace) recorded in a trabecula from an old dog before and after exposure to Mex (10 μM). Twitches and first derivative of developed tension are superimposed in inset. B: data are shown as mean ± SE (adult: n = 6 muscles, 5 dogs, 5.0 ± 0.6 yr; old: n = 10 muscles, 7 dogs, 12.6 ± 0.4 yr). *P < 0.01 vs. KHB. C: isometric contraction (top trace) and first derivative of developed tension (bottom trace) recorded in a trabecula from an old dog before and after exposure to low dose of TTX (1 μM). D: data for developed tension in 3 trabeculae before and after exposure to TTX (1 μM) or Ran (10 μM). Trabeculae were obtained from 2 old dogs (11.3 and 14.3 yr old). E: data for developed tension, normalized with respect to CL 2,000 ms, are shown as mean ± SE (adult: n = 5 muscles, 4 dogs, 5.3 ± 0.6 yr; old: n = 4 muscles, 3 dogs, 12.3 ± 0.7 yr). *P < 0.05 vs. KHB; †P < 0.01 for various frequencies within the same group.