Ruthenium red causes reversible synaptic depression in crayfish extensor muscles

Abstract

Cells, especially those involved in synaptic transmission, keep intracellular calcium concentration low for proper functioning. In addition to pumping calcium out via ATP-powered pumps, the cell also stores calcium within organelles such as the endoplasmic reticulum and mitochondria to remove it from the cytoplasm. Mitochondria specifically use the mitochondrial uniporter to take up calcium from the cell. We used ruthenium red, a mitochondrial uniporter channel inhibitor, to test how the inhibition of the uniporter channel affects synaptic transmission. We found that under low and high frequency stimulation, the application of ruthenium red depressed excitatory postsynaptic potentials (EPSPs) over time. Additionally, the presence of the potassium channel inhibitor 4-AP with ruthenium red under high frequency stimulation did not influence the effectiveness of ruthenium red’s inhibition. Compared to 4-AP alone, a combination of both chemicals produced a faster and stronger depression of EPSPs. After a test including both chemicals, removing ruthenium red while leaving 4-AP allowed some recovery from the inhibitory effect of ruthenium red, as EPSPs remained partially depressed under 4-AP alone. In all experiments, the depression resulting from either chemical was reversible. The same EPSPs recovered to their previous EPSPs after a wash with normal crayfish Ringer’s solution. From our findings, we can conclude that ruthenium red produces reversible synaptic depression in crayfish extensor muscles.