Safety factor for neuromuscular transmission at type‐identified diaphragm fibers

Abstract

The safety factor (SF) for neuromuscular transmission varies across limb muscles of different fiber-type composition. Using intracellular recordings in rat diaphragm fibers, we found that SF varies across muscle fiber types (even within a single muscle), being larger for type IIx or IIb fibers than for type I or IIa fibers. Fiber-type differences in activation history or mechanical load may contribute to differences in SF and are important determinants of neuromuscular plasticity.

Neuromuscular transmission modulation by adenosine upon aging

“…However, in a previous work (see Ginsborg and Hirst, 1972) the initial quantal content of EPPs (either being low, in experiments where muscle contractions were paralyzed by high magnesium, or high in the experiments where muscle contractions were paralyzed by tubocurarine) did not influence the inhibitory effects of adenosine at the rat diaphragm neuromuscular junction. How adenosine influences safety factor variability in nerve terminals innervating different fiber types (see Ermilov et al, 2007) cannot be answered in the present work and awaits further investigation.…”

“…Whether such differences might influence the presently reported effects of adenosine upon aging, needs to be explored at the light of the results obtained by Rowley et al (2007) and Ermilov et al (2007). However, in a previous work (see Ginsborg and Hirst, 1972) the initial quantal content of EPPs (either being low, in experiments where muscle contractions were paralyzed by high magnesium, or high in the experiments where muscle contractions were paralyzed by tubocurarine) did not influence the inhibitory effects of adenosine at the rat diaphragm neuromuscular junction.…”

“…Neuromuscular junctions differ in quantal content, safety factor, and adaptation to repetitive activation (see Ermilov et al, 2007;Rowley et al, 2007). Whether such differences might influence the presently reported effects of adenosine upon aging, needs to be explored at the light of the results obtained by Rowley et al (2007) and Ermilov et al (2007).…”

Neurotrophins improve synaptic transmission in the adult rodent diaphragm

“…The subset of synaptic vesicles docked at the specialized release sites (active zones) is termed the "readily releasable" pool (RRP); it can be identified in electron micrographs directly across from the postsynaptic folds [19,20]. Importantly, only a fraction of these vesicles are released with each arriving presynaptic impulse [21,22]. Synaptic vesicles located in close proximity (but not docked) to active zones do not contribute to neurotransmitter release until recruited to the RRP; they comprise the so-called "cycling" pool [23,24].…”

Key aspects of phrenic motoneuron and diaphragm muscle development during the perinatal period

“…For instance, the amplitude of excitatory postsynaptic potentials correlates with the input resistance of the motoneuron (15). The safety factor for neuromuscular transmission (defined as the ratio of the excitatory postsynaptic potential amplitude to activation threshold of a muscle fiber) varies across fiber types, being larger for type IIb DIAm fibers than for type I or IIa fibers (25). With repeated activation, the amplitude of excitatory postsynaptic potentials declines to a greater extent at terminals of type I or IIa fibers than at type IIb fibers (79).…”