Speed of repolarization and morphology of glygerol-treated frog muscle fibres.
1. Single muscle fibres from frog semitendinosus were subjected to sudden changes in [K](o), while recording membrane potential.2. In agreement with Hodgkin & Horowicz (1960), a sudden increase in [K](o) in normal fibres produced a rapid depolarization (half-time 0.3 sec), whereas a sudden decrease in [K](o) produced a slower repolarization (half-time 2-3 sec).3. Fibres were subjected to ;glycerol-treatment', a procedure which was supposed to produce a functional disconnexion of the T-system from the surface. In these glycerol-treated fibres both depolarization and repolarization induced by changes of [K](o) took place rapidly.4. The results suggest that the slowness of the repolarization in normal fibres is due to a retention of K ions inside the T-tubules.5. Electron microscopical observation of single fibres or bundles of fibres, which have been soaked in a Ringer containing ferritin, revealed that normal fibres contained ferritin particles in the T-system, while glycerol-treated fibres showed no ferritin. Except for the presence of some large vacuoles and some swelling of the T-system, glycerol-treated fibres appeared morphologically normal.6. Prolonged soaking in a high potassium solution produced electrical effects suggesting that K ions can enter the tubules of treated fibres very slowly, in spite of their inaccessibility to ferritin.7. The main effect of glycerol-treatment does not seem to be a total disconnexion of the T-system from the fibre surface, but rather constriction of the T-tubules near their openings to the exterior.
D000818:Animals; D001001:Anura; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D005293:Ferritins; D005990:Glycerol / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008854:Microscopy, Electron; D009210:Myofibrils / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011896:Rana temporaria; D012519:Sarcoplasmic Reticulum / Q000187:drug effects; D013997:Time Factors; D014981:Xenopus
D005293:Ferritins; D005990:Glycerol; D011188:Potassium