Properties of synaptic transmission at the neuromuscular junction of the squid, Loligo opalescens

1. 1. Spontaneous and evoked synaptic activity were recorded from the muscles of squid fin and mantle. These spontaneous synaptic potentials were large (up to 30 mV) and pleomorphic. Their amplitudes were not normally distributed, nor did they appear to be clustered in integral multiples of some “unit” event size. 2. 2. Electrical stimulation of the nerve resulted in muscle twitches when the bath calcium concentration was a third normal or higher. The frequency of spontaneous synaptic events was unaffected by low calcium. 3. 3. The large size of spontaneous events may mean that the synchronized release of only a few such “quanta” are sufficient to cause muscle action potentials and contraction. 4. 4. The shapes of spontaneous events correlated poorly with their amplitudes, which is consistent with release from multiple synaptic sites with distinct properties.