IMPROVED STABILITY OF DROSOPHILA LARVAL NEUROMUSCULAR PREPARATIONS INHEMOLYMPH-LIKE PHYSIOLOGICAL SOLUTIONS

Neuromuscular preparations from third instar larvae of Drosophila are not well-maintained in commonly used physiological solutions: vacuoles form in the muscle fibers, and membrane potential declines. These pro blems may result from the Na:K ratio and total divalent cation content of these physiological solutions being quite different from those of haemolymph. Accordingly haemolymph-like solutions, based upon ion meas urements of major cations, were developed and tested. Haemolymph-like solutions maintained the membrane potential at a relatively constant l evel, and prolonged the physiological life of the preparations. Synapt ic transmission was well-maintained in haemolymph-like solutions, but the excitatory synaptic potentials had a slower time course and summat ed more effectively with repetitive stimulation, than in standard Dros ophila solutions. Voltage-clamp experiments suggest that these effects are linked to more pronounced activation of muscle fiber membrane con ductances in standard solutions, rather than to differences in passive muscle membrane properties or changes in postsynaptic receptor channe l kinetics. Calcium dependence of transmitter release was steep in bot h standard and haemolymph-like solutions, but higher external calcium concentrations were required for a given level of release in haemolymp h-like solutions. Thus, haemolymph-like solutions allow for prolonged, stable recording of synaptic transmission.