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  • Title: Ba2+ ions block K+-induced contractures by antagonizing K+-induced membrane depolarization in frog skeletal muscle fibres.
    Author: Frank GB, Rohani F.
    Journal: Can J Physiol Pharmacol; 1982 Jan; 60(1):47-51. PubMed ID: 6279259.
    Abstract:
    The effects of Ba2+ ions on twitches, K+-induced contractures, and on intracellularly recorded membrane potentials (Em) and depolarizations of frog skeletal muscle fibres were investigated. Exposure of toe muscles to choline--Ringer's solution with 10(-3) M Ba2+ with Ca2+ (1.08 mM) eliminated or very greatly reduced contractures produced by 60 mM K+. In contrast, not only did the same concentration of Ba2+ ions fail to depress the twitch tension of isolated semitendinosus fibres when added to Ringer's with Ca2+, but it even restored twitches that had been eliminated in a zero Ca2+ Ringer's solution. The resting Em of sartorius muscle fibres in choline--Ringer's solution was reduced about 20 mV by 10(-3) M Ba2+. This Ba2+ ion concentration also antagonized the K+-induced depolarization. Thus in the presence of 1 mM Ba2+, 20 mM K+ hyperpolarized rather than depolarized the fibres and 60 or 123 mM K+ produced only very slowly developing, small depolarizations. These results suggest that the loss of the K+-induced contracture in choline-Ringer's caused by Ba2+ ions is due to an inhibition of the K+-induced depolarization. The latter result is consistent with previous findings of other workers that Ba2+ ions block membrane K+ channels.
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