Evoked transmitter release at neuromuscular junctions in wild type and cysteine string protein null mutant larvae of Drosophila.

Cysteine string proteins (CSPs) are synaptic vesicle proteins thought to be involved in neurotransmitter release. To obtain more information about the function of these proteins motor nerve terminals of wild type and CSP null mutant Drosophila larvae were depolarized and excitatory postsynaptic currents (EPSCs) were recorded with an extracellular electrode at 16-18 degrees C. At this temperature the amplitude of average EPSCs was reduced and the time constant of the exponential fit of the current decay was increased in CSP null mutant compared to wild type larvae. The number of quanta released per pulse was not different but the time course of release was distributed differently in CSP null mutant and wild type larvae. In measurements of the latency of quantal EPSCs the probability of release after a pulse reached a lower peak value and the decay after the peak was delayed in CSP null mutant compared to wild type larvae. In addition facilitation in response to twin-pulse stimulation was slightly increased at low levels of release in CSP null mutant larvae. It is concluded that CSPs are involved in neurotransmitter release and help to synchronise evoked release at nerve terminals.