[Miniature potentials in fast and slow muscle fibers in the locust]

The miniature excitatory postsynaptic potentials were studied in the fast and slow fibres of Locusta migratoria by means of intracellular microelectrodes. Statistical analysis indicated that the spontaneous transmitter release can be predicted by the negative binomial formula with a 85% reliability. It shows that there is certain mutual interaction between the processes responsible for the spontaneous release of the transmitter from locust nerve terminals. In the calcium-free solutions frequency of miniature potentials was reduced to about 83.5% in the fast muscle fibres and to about 96.3% in the slow muscle fibres. A study of Mg++ effect on frequency of miniature potentials showed that 10 mM Mg++ reduced the frequency to about 75% in the fast muscle fibres and to about 90% in the slow ones. The conclusion is drawn that in the fast and slow muscle fibres the nerve terminals possess different sensitivity to the changes in ionic composition of the environment.