Change of statistical parameters of transmitter release during various kinetic tests in unparalysed voltage‐clamped rat diaphragm.

Abstract

The statistical nature of transmitter release was studied in unparalyzed cut rat diaphragm using a voltage clamp technique at room temperature (23.degree. C). While the binomial distribution described observed amplitude histograms well, the Poisson distribution was clearly inadequate. Values of m ranged from 40-45, while values for n varied from 45-53 and p was between 0.82 and 0.90. Estimation of the probability of release from the transient decay of EPC [end plate currents] in short tetanic trains (11 pulses, 150 Hz) gave values of p from 0.031 to 0.054, which are > 1 order of magnitude lower than statistical estimates. As a result of the short tetanic stimulation (5 pulses, 20, 50 and 100 Hz) there was an initial transient facilitation which afterwards became masked by depression. Statistical analysis suggested that the changes in the average numbers of quanta released (m) could be attributed to the change in the immediatley available store (n). During long tetanic stimulation (4000 pulses, 10-100 Hz) statistical analysis suggests that the decrease in the average number of quanta released (m) could be attributed almost entirely to the decrease in the immediately available store (n). The probability of.release (p) decreased only slightly. The extent of the post-tetanic potentiation indicates that it cannot be explained on the grounds of increased probability of release (p) only. There should be an increase as well in the immediately available store (n). While depression is most likely caused by the depletion of the immediately available store due to insufficient replenishment, the facilitation is probably caused by the increase in the capacity of the immediately available store to contain transmitter.