Uptake of Ruthenium Red by the Sensory Nerve Terminal of the Frog Muscle Spindle

Abstract

Electron microscopic studies revealed ruthenium red (RuR) to be taken up by sensory nerve terminals of the isolated frog muscle spindle, after incubation in 0.2 mM RuR for 10 min, a treatment which is known to modify the sensory response. Elevtron-dense deposits, found to contain ruthenium ions by X-ray microanalysis, occurred in the cytoplasm and mitochondria of the sensory terminals and intrafusal muscle fibers, and in the cells of the inner and outer capsules. Preincubation in 0.5 mM RuR for 10 min resulted in swelling of the sensory nerve terminals in which the distinction between cytoplasm and mitochondria was abolished. These results suggest that RuR may modify the terminal responses by modulating the intracellular ionic composition of the terminals.