title: Depolarization accelerates the decay of K+ contractures in rat skeletal muscle fibers.
abstract: The experiments examine the effects of membrane potential on the time course of K+ contractures in small bundles of rat soleus and extensor digitorum longus (EDL) muscle fibers. Control K+ contractures were induced by exposure to a 200 mmol/L K+ solution in polarized fibers with a resting membrane potential of -83 mV (3.5 mmol/L K+), while test contractures were evoked with 200 mmol/L K+ from -46 mV, after 5, 10, and 30 min in a 30 mmol/L K+ conditioning solution. The decay times of the test K+ contracture in depolarized fibers were faster than those of the control K+ contracture in both soleus and EDL. A maximum reduction of 60% in the time for the contracture to decay from 90% to 10% was seen in soleus fibers after depolarizations lasting 10 min, while a reduction of 45% was seen in the decay time of EDL fibers after a 5-min depolarization. The amplitudes of the test contractures were 30% less than control after 5-min and 10-min depolarization and 50% less than control after 30 min. Analysis of the results suggests that the kinetics of excitation-contraction coupling may be altered in damaged muscle fibers.
authors: Muscle Research Group, John Curtin School of Medical Research, Australian National University, Canberra City, Australia.
authors: M F
authors: MF
authors: Patterson
authors: J
authors: J
authors: Mould
authors: A F
authors: AF
authors: Dulhunty
mesh_terms: D000818:Animals; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D011188:Potassium