The distribution of cholinesterase (Ch-esterase) in isolated myelinated fibers of the frog has been investigated. Quantitative microgasometric measurements have confirmed the previous histochemical observations. Both approaches indicate that in frog nerve fibers acetylcholinesterase (ACh-esterase) is the only or the predominant enzyme when selective inhibitors and different substrates are used: acetylcholine (ACh), butyrylcholine, and acetyl-B-methylcholine (Mecholyl). By means of the microgasometric technique, a significant difference in ACh-esterase activity between axons isolated from ventral (37.2 ± 1.7 µmole x 10-5 ACh/mm2/hr) and dorsal roots (2.0 ± 0.9 µmole x 10-5 ACh/mm2/hr) was found. In the region of the node of Ranvier the enzyme activity (50.4 ± 4.4 µmole x 10-5 ACh/mm2/hr) appears to be considerably higher than in the internodal area (36.6 ± 2.1 µmole x 10-5 ACh/mm2/hr). The findings are discussed in relation to the theory of saltatory conduction and the ACh system.

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