Effects of ruthenium ions on the sensory terminal discharges of the frog muscle spindle

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.

The spindle potential in the frog muscle spindle does not require external Na+

Spindle potential recorded from the sensory nerve terminal of isolated frog muscle spindles disappeared within 20-30 min after the spindle receptor was perfused with Na+-free (Li, Tris or choline) Ringer's solution, whereas the amplitude of spindle potential was not attenuated for periods up to 60 min when the spindles were perfused in a Na+-free Ringer's solution containing both 10 mM TEA and 0.1 mM 4-aminopyridine after being washed with a normal Ringer's solution containing both the K+-channel blockers. It is concluded that the time-dependent decrease in the amplitude of spindle potential during the application of Na+-free solution is not ascribable to a decrease in the inward current carried by Na+, but is due to an increase in an outward current carried by K+.