AJP - Endocrinology and Metabolism, Vol 242, Issue 3 193-E200, Copyright © 1982 by American Physiological Society
Intracellular Na+ and K+ activities during insulin stimulation of rat soleus muscle
R. J. Stark and J. O'Doherty
The action of insulin on the resting membrane potential (Em) and
intracellular sodium and potassium activities (aNa, aK) of rat soleus
muscle fibers was determined by direct intracellular measurements of aNa,
aK, and Em using Na-selective, K-selective, and conventional
microelectrodes. The use of these microelectrodes allowed us to
continuously monitor these parameters in the same fiber. Although we were
able to accurately measure aNa and aK and continuously monitor their levels
throughout periods of insulin stimulation of up to 20 min duration, we were
unable to detect any significant change in Em, aNa, or aK. Varying the
concentration of insulin or extracellular glucose failed to alter our
observations. These results indicate that the action of insulin on the
sarcolemma and subsequent increase in glucose transport must result from
some mechanism independent of a change in membrane potential or
intracellular sodium or potassium activity.
