Presynaptic Changes Accompanying Transmission of a Single Nerve Impulse: An Interdisciplinary Approach Using Rapid Freezing
By rapid freezing of single isolated prisms (columns of electroplaques), we have been able to study changes in presynaptic ACh stores with a time resolution about the same as the duration of a burst of 20 single impulses at 100Hz. (Such bursts are very similar to the activity of the electric organ of Torpedo in its natural habitat.) Freeze-fracture morphology of the presynaptic membrane during and after a single impulse is also possible for the rapidly frozen tissue, and preliminary results indicate changes in the membrane during this time.
It is well known that 4-aminopyridine (4-AP) has a strong potentiating action at cholinergic synapses. For the Torpedo electric organ this action is predominantly one of increasing the duration of the electrical response, rather than its amplitude. The duration may be increased more than 100 times. Because this duration is much longer than the time resolution of our freezing experiments, we have been able to use rapid freezing to study both biochemical and morphological changes during the whole time course of the greatly prolonged single impulse which occurs in the presence of 4-AP.
KeywordsElectric Organ Presynaptic Membrane Rapid Freezing Cholinergic Synapse Single Impulse
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