Figure 8.

Ouabain caused greater loss of tetanic force and membrane depolarization in HyperKPP, EDL, and soleus than in diaphragm. (A–C) All muscles were allowed a 30-min equilibrium at 4.7 mM K⁺ before any measurements or changes in [K⁺]_e or ouabain. For force measurements, muscles were exposed 20 min to ouabain while being exposed to 4.7 mM K⁺ before [K⁺]_e was increased to 9 mM, still in the presence of ouabain as indicated in the figures. A similar approach was used for resting EM with half the muscles; for the other half, muscles were exposed to ouabain only after [K⁺]_e had been raised to 9 mM K⁺. The resting EM at 9 mM and 1 µM ouabain was not different between the two approaches, so the data were pooled. Error bars represent SEM; force of five muscles; resting EM: 70–93 fibers/9 muscles at 4.7 mM K⁺ and 39–80 fibers/6 muscles for all other conditions. *, Mean tetanic force or resting EM of HyperKPP muscle was significantly different from the mean values of wild-type muscle, ANOVA, and LSD, P < 0.05.