title: The effects of glycerol and urea on the ultrastructure and contractility of fast and slow rat skeletal muscles.
abstract: The influence of the influx and efflux of glycerol and urea (400 mmol/l) on the amplitude of isometric twitches and the ultrastructure of isolated fast (EDL) and slow (SOL) muscles of young rats was studied. The influx of non-electrolytes was accompanied by a temporary decrease in the twitch tension. The removal of non-electrolytes resulted in a stable reduction of twitches. Both effects were less pronounced in glycerol experiments on slow muscles. The inhibition of twitches after the removal of non-electrolytes was associated with selective alterations of the T-system: swelling, vacuolation, and lysis of T-tubules. Quantitative analysis of the T-system showed that the extent of these changes may vary for different fibres, and the intensity of morphological alteration of the T-system generally correlated with the degree of twitch inhibition. Reloading of muscles with non-electrolytes tended to improve the T-system structure in some fibres and led to a partial restoration of the amplitude of twitches.
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D005990:Glycerol / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000502:physiology / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains; D014508:Urea / Q000494:pharmacology*
chemical_list: D014508:Urea; D005990:Glycerol