End-plate potentials were recorded from the frog sartorius nervemuscle preparation under conditions of low quantal content (0.5-0.6mM Ca, 5mM Mg) to examine the effects of repetitive stimulation on the increased transmitter release resulting from augmentation, a process which decays with a time constant of about 7 sec. When the conditioning stimulation rate was doubled from 10 to 20/sec the magnitude of augmentation immediately following a 200 impulse conditioning train was increased from 1.5±0.36 to 2.5±0.64 while the time constant of decay decreased from 7.7±0.53 to 6.8±0.33 sec (mean±S.E., N=13). When the stimulation rate was kept constant at 20/sec, increasing the number of conditioning impulses from 100 to 400 led to a 1.4-5.8 times increase in the magnitude of augmentation immediately following the conditioning train but had little effect on its time constant of decay. In about 1/3 of the experiments the increase in the magnitude of augmentation started to approach a steady-state level after about 15-20 sec of conditioning stimulation. In the remaining experiments the magnitude of augmentation did not approach a steady-state level but increased continuously during the conditioning stimulation. The first type of response could be described with either a linear or 4th power accumulation model (J. Physiol. 245:183-208). To describe the second type of response it was necessary to assume that the increment of augmentation added by each conditioning impulse increased by a constant percent (0.06-0.7%) with each impulse.
|Original language||English (US)|
|State||Published - Jan 1 1977|
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