THE EFFECT OF BA IONS ON HUMAN MUSCLE CULTURED IN MONOLAYER AND INNERVATED WITH FETAL-RAT SPINAL-CORD

In human muscle culture, 7% of aneurally (AMs) and 5.9% of innervated contracting muscle cells (ICMs) showed slow repolarization components (SRCs: duration, less than 10 ms) of action potentials. After an application of 10 mM Ba ion, prolonged SRCs, which were blocked by nifedipine, appeared in 96% of the AMs and 70% of the ICMs. The duration of SRCs under the application of 10 mM Ba solution were not significantly different between AM and ICM (2.8 and 2.0 s, respectively). The resting membrane potentials (RMPs) of AMs and ICMs decreased to 78% and 74% in the medium with 10 mM Ba solution, respectively, and the input resistance (Rin) of AM increased to 161% in the medium with 10 mM Ba. Slow hyperpolarizing afterpotentials were observed both in AMs and ICMs, and completely disappeared during the application of Ba. © 1990.