Morphological and Physiological Changes in Dissociated Adult Frog Muscle Fibres after Prolonged Culturing

Adult frog (Rana temporaria) muscle fibres, denervated in vivo, were dissociated and maintained in culture for several weeks. Light and electron microscopical studies showed that the fibres developed striated muscle sprouts. These sprouts were in cytoplasmic continuity with the parent muscle fibre. To judge by the presence of miniature endplate potentials, embryonic Xenopus laevis neurons were able to form functional neuromuscular junctions, both on the muscle sprouts and on the parent fibre. In addition to the usual depolarizing action potentials, the cultured fibres, with or without sprouts, showed slow hyperpolarizing regenerative responses. These hyperpolarizing action potentials were triggered when the membrane potential reached about -120 mV and their `peak' amplitude was at about -230 mV. It is concluded that new skeletal muscle fibres can be formed from outgrowths of adult muscle fibres, and that these sprouts can accept motor innervation.