There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The avermectins are a family of novel macrocyclic lactones which paralyze nematodes
and insects. One highly potent member of this family, avermectin B1a, has been shown
to block neuromuscular transmission in the lobster opener and stretcher muscles. Continuous
superfusion of these muscles with the drug (6 microM) resulted in a rapid loss of
intracellularly recorded inhibitory postsynaptic potentials. Amplitudes of excitatory
potentials and membrane input resistance declined at a slower rate, with a similar
time course (25-30 min). These effects were not reversed by prolonged washing. A 3-5
mV hyperpolarization was also observed, which was reversed to depolarization in low
chloride lobster saline. Picrotoxin (20 microM) blocked the effects of avermectin
B1a on excitatory postsynaptic potentials. Both gamma-aminobutyric acid (GABA) and
avermectin B1a decreased the slope of current voltage curves in the stretcher muscle,
reflecting an increase in membrane conductance. These changes were greatly reduced
by application of bicuculline (50 microM) or picrotoxin (20 microM) Avermectin B1a
had no effect on the "fast" axon excitatory electrical responses (glutaminergic) of
the cockroach extensor tibiae muscle fibers which lack an inhibitory (GABAergic) input.
It is concluded that at the lobster neuromuscular junction, avermectin B1a acts on
the GABAergic synapse and lowers input resistance of the muscle membranes by causing
an increase in chloride ion permeability.