Diversity among mouse motor nerve terminals with respect to release transmitter quanta

Abstract

1. 1. The aim of this work was to reexamine whether a positive correlation exists between the frequency ( F, sec −1) of miniature endplate potentials (m.e.p.ps) and the quantal content ( m) of endplate potentials (e.p.ps) or between quantal content, frequency and twin-pulse facilitation of transmitter release at a large number of neuromuscular junctions in the mouse. 2. 2. The values of F and m were both measured intracellulary at endplates of mouse diaphragm in a high Mg 2+/low Ca 2+ bathing solution. 3. 3. Values of both F and m varied from junction to junction. Smaller values of F were correlated with smaller values of m, and vice versa, resulting in a linear relationships. Histograms of F and m were skewed towards smaller values. 4. 4. E.p.ps evoked by twin pulses gave the quantal contents of the first ( m1) and second ( m2) responses. 5. 5. The ratio of m 2 to m1 varied from junction to junction. A histogram of this ratio was skewed towards smaller values. 6. 6. The ratio of m2 to m1 showed larger fluctuations at junctions with smaller values of F or m1 but was focused around 1 at junctions with larger values of F or m1. 7. 7. The skewed parts of the histograms of F, m and m2/ m1 accounted for the major population of junctions. 8. 8. These results support the hypothesis that an intrinsic ability to release transmitter plays a role in regulation of the evoked output of transmitter at neuromuscular junctions in the mouse. 9. 9. Such an ability is not correlated with the twin-pulse facilitation of transmitter release.