Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus

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Acta Neurobiologiae Experimentalis

Nencki Institute of Experimental Biology

Polish Neuroscience Society

Subject: Behavioral Sciences , Biomedical Sciences & Nutrition , Life Sciences , Medicine , Neurosciences

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ISSN: 0065-1400
eISSN: 1689-0035

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VOLUME 76 , ISSUE 2 (June 2016) > List of articles

Advertisement Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus

Hanna Drzymała-Celichowska * / Rositsa Raikova / Piotr Krutki

Keywords : sag, force potentiation, slow motor unit, soleus, sex differences, mathematical decomposition, rat

Citation Information : Acta Neurobiologiae Experimentalis. Volume 76, Issue 2, Pages 152-157, DOI: https://doi.org/10.21307/ane-2017-014

License : (CC BY 4.0)

Received Date : 18-January-2016 / Accepted: 03-May-2016 / Published Online: 25-July-2017

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ABSTRACT

Slow motor units (MUs) have no sag in their unfused tetani. This study in anesthetized rats shows that the sag can be observed in slow soleus MUs after prolonged activity. Twitches and unfused tetanic contractions were recorded from male (n=35) and female (n=39) MUs before and after the four minutes of the fatigue test (trains of 13 pulses at 40 Hz repeated every second). After this activity twitch contractions potentiated and a shift in the steep part of the force-frequency curve towards lower frequencies was observed in both sexes. Initially no sag was visible in unfused tetani, but after the fatigue test the phenomenon was observed in 77% of male and in 13% of female MUs, with the sex difference possibly related to a higher content of IIa myosin and faster MU contraction in male soleus. Decomposition of tetani with sag into trains of separate twitches elicited by successive stimuli revealed higher forces for the initial than subsequent twitches. The newly revealed enhancement of the sag in force development following long-lasting activation is more pronounced in males than in females.

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