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Relations between excitability and contractility in rat soleus muscle: role of the Na + ‐K + pump and Na + /K + gradients
Author(s) -
Overgaard Kristian,
Nielsen Ole Bækgaard,
Flatman John A.,
Clausen Torben
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0215r.x
Subject(s) - chemistry , stimulation , contractility , tetanic stimulation , tetrodotoxin , medicine , biophysics , endocrinology , biochemistry , neurotransmission , receptor , biology
1 The effects of reduced Na + /K + gradients and Na + ‐K + pump stimulation on compound action potentials (M waves) and contractile force were examined in isolated rat soleus muscles stimulated through the nerve. 2 Exposure of muscles to buffer containing 85 mM Na + and 9 mM K + (85 Na + /9 K + buffer) produced a 54 % decrease in M wave area and a 50 % decrease in tetanic force compared with control levels in standard buffer containing 147 mM Na + and 4 mM K + . Subsequent stimulation of active Na + ‐K + transport, using the β 2 ‐adrenoceptor agonist salbutamol, induced a marked recovery of M wave area and tetanic force (to 98 and 87 % of the control level, respectively). Similarly, stimulation of active Na + ‐K + transport with insulin induced a significant recovery of M wave area and tetanic force. 3 During equilibration with 85 Na + /9 K + buffer and after addition of salbutamol there was a close linear correlation between M wave area and tetanic force ( r = 0 ·92, P < 0·001). Similar correlations were found in muscles where tetrodotoxin was used to reduce excitability and in muscles fatigued by 120 s of continuous stimulation at a frequency of 30 Hz. 4 These results show a close correlation between excitability and tetanic force. Furthermore, in muscles depressed by a reduction in the Na + /K + gradients, β‐adrenergic stimulation of the Na + ‐K + pump induces a recovery of excitability which can fully explain the previously demonstrated recovery of tetanic force following Na + ‐K + pump stimulation. Moreover, the data indicate that loss of excitability is an important factor in fatigue induced by high‐frequency (30 Hz) stimulation.