Journal of Neuroscience, Vol 5, 2212-2224, Copyright © 1985 by Society for Neuroscience
Gating properties of acetylcholine receptors at developing rat endplates
S Vicini and SM Schuetze
The gating properties of acetylcholine receptors (AChRs) change during the
development of rat soleus endplates. During the first 3 weeks after birth,
the apparent mean channel open time (tau) decreases severalfold and the
single-channel conductance (gamma) increases 50%. To better understand this
phenomenon, we used a combination of noise analysis, analysis of miniature
endplate currents (MEPCs), and single-channel recordings to quantify the
relative levels of fast and slow AChR activity at developing soleus
endplates. When the same endplates were studied with both noise analysis
and MEPC analysis, results obtained with the two techniques were strongly
correlated, but MEPC analysis yielded higher estimates of the relative
amount of slow channel activity. Experiments designed to examine the
distribution of fast and slow channels gave no evidence for a gradient of
either channel type within individual endplates; rather, fast and slow
channels appeared to be mixed together. However, the relative amount of
fast and slow channel activity did vary markedly among different endplates
within individual muscles. In agreement with earlier studies, we found a
progressive decrease in the relative amount of slow channel activity during
the first 3 weeks after birth. However, our data indicate that this process
begins sooner than reported previously and takes longer to complete. Some
of the same endplates that were studied physiologically were also examined
in the electron microscope to test the hypothesis that changes in AChR
gating might be related to ultrastructural changes such as the formation of
folds. The physiological and ultrastructural results were essentially
uncorrelated.
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