saxitoxin and Potassium-Deficiency

The dependence of contractile performance on the leak-to-pump ratio for Na+ has been examined. In isolated rat soleus muscle the concentration of Na(+)-K+ pumps was shown to decrease with age (-57%) or K+ deficiency (-69%), whereas Na+ channel concentration remained constant. This relative increase in the ratio between Na+ channels and Na(+)-K+ pumps was associated with a markedly faster rate of force decline (58 and 97%, respectively; both P < 0.001) during stimulation at 90 Hz and reduced subsequent force recovery (-34 and -38%, respectively; both P < 0.001). Similar effects were elicited by acute inhibition of Na(+)-K+ pump activity with ouabain. Preincubation with aconitine and veratridine, resulting in a 91 and 118% increase in Na+ influx per contraction, respectively (both P < 0.05), significantly hastened the initial rate of force decline (19%; P < 0.05 for aconitine and 69%; P < 0.001 for veratridine) and slowed recovery (-59 and -86%, respectively, both P < 0.001). It is concluded that the ratio between excitation-induced Na+ influx and Na(+)-K+ pump capacity is an important determinant for endurance and rate of recovery of force in skeletal muscle.

Topics: Aconitine; Age Factors; Animals; Electric Stimulation; Female; In Vitro Techniques; Muscle Contraction; Muscle, Skeletal; Ouabain; Potassium Deficiency; Protein Binding; Rats; Rats, Wistar; Saxitoxin; Sodium Channel Agonists; Sodium Channels; Sodium-Potassium-Exchanging ATPase; Veratridine