Evidence that ruthenium red disturbs the synaptic transmission in the rat hippocampal slices through interacting with sialic acid residues.

Ruthenium red (RR) at a concentration of 0.71 mM selectively blocked synaptic transmission in hippocampal slices. Antidromically evoked potentials and fibre potentials were only little affected. The action of RR was reversible by washout, but only following shorter (40-50 min) times of incubation. After longer incubation times (hours), the abolished population spike did not recover after washout but could be restored by facilitation of the calcium transport into the nerve terminal with 3,4-diaminopyridine. Partial liberation of sialic acid with neuraminidase from Vibrio Cholerae markedly increased the time after which the potential was abolished by RR. Exogenously added gangliosides and sialic acid also delayed the action of RR. Calcium at a concentration of 13.2 mM prevented or reduced the RR effect. It is concluded that RR binds to sialic acid residues, interfering with neurotransmission by disturbing the calcium transport into the cell.