title: Effects of ammonium ions on the depolarization-induced and direct activation of the contractile apparatus in mechanically skinned fast-twitch skeletal muscle fibres of the rat.
abstract: Mechanically skinned fibre preparations from the extensor digitorum longus muscle of the rat were used to test whether a rise in myoplasmic [NH+4] in the range 2-10 mM interferes with the mechanism of excitation-contraction coupling in fast-twitch mammalian muscle. Under our conditions (pH 7.10, Mg2+ 1 mM, temperature 23 degrees C), [NH+4] up to 10 mM had little effect on the Ca(+)-activated force and on the peak of the t-system depolarization-induced force response. However, the duration of the depolarization-induced force response was decreased significantly at [NH+4] > or = 2 mM. From these data we conclude that the intracellular accumulation of NH+4 is not likely to play a major role in fatigue. Nevertheless, the build up of NH+4 during fatigue, may have a significant inhibitory effect on the force output by decreasing the duration of the t-system depolarization-induced activation of the contractile apparatus.
authors.affiliation: Department of Chemistry and Biology, Victoria University of Technology, Melbourne, Australia.
authors.forename: G M
authors.initials: GM
authors.lastname: Stephenson
authors.forename: D G
authors.initials: DG
authors.lastname: Stephenson
mesh_terms: D000818:Animals; D002021:Buffers; D002118:Calcium / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D007477:Ions; D008082:Lipotropic Agents / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D018763:Muscle Fatigue / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology
chemical_list: D002021:Buffers; D007477:Ions; D008082:Lipotropic Agents; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D002794:Choline; D002118:Calcium