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Department of Physiology, University of Aarhus, DK-8000 Aarhus C, Denmark
In
isolated soleus muscles of 4-wk-old rats, M wave parameters were
recorded with surface and deep recording electrodes and examined in
relation to both twitch and tetanic force. Addition of ouabain
(10
5 M for 16 min) to
isolated muscles caused an ~40% decrease in twitch amplitude and
area (P < 0.01) that was associated
with a 98% decrease in surface M wave amplitude, a 78% decrease in deep M wave amplitude (both P < 0.001), a 98% decrease in surface M wave area
(P < 0.01), 48% of which occurred
within 60 s of addition of ouabain (P < 0.05), and a 55% decrease in deep M wave area (P < 0.05). The decrease in twitch
parameters on addition of ouabain was most closely correlated with deep
M wave area (r = 0.92). Direct tetanic
stimulation at a frequency of 30 Hz resulted in an initial potentiation
of M waves, which was not seen at a frequency of 90 Hz. Instead, 90 Hz
stimulation resulted in a prompt decrease in tetanic force that was
correlated with a decrease in both deep M wave amplitude
(r = 0.94;
P < 0.01) and deep M wave area
(r = 0.96;
P < 0.01). It is concluded that
simultaneous surface and deep recordings involving area and amplitude
are fundamental to analysis of the effects of pharmacological agents on
muscle performance and the use of M waves as predictors of muscle excitability.
skeletal muscle; compound action potential; electromyogram; ouabain; Na+-K+ pump
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