Evaluation of Presynaptic Action of Depolarizing Neuromuscular Blocking Agents with Single Twitch Response in Vitro.

Hwang,  Kyung Ho; Chai,  Won Seok; Kang,  Kyu Sik; Kim,  Yong Ik; Park,  Wook; Kim,  Sung Yell

doi:2001.40.4.532

Experimental Research Article

Korean Journal of Anesthesiology 2001;40(4):532-537.
DOI: https://doi.org/10.4097/kjae.2001.40.4.532

Evaluation of Presynaptic Action of Depolarizing Neuromuscular Blocking Agents with Single Twitch Response in Vitro.

Kyung Ho Hwang, Won Seok Chai, Kyu Sik Kang, Yong Ik Kim, Wook Park, Sung Yell Kim

Department of Anesthesiology, School of Medicine, Soonchunhyang University, Bucheon, Korea.

Abstract

BACKGROUND
This study was performed to evaluate the presynaptic effects of depolarizing neuromuscular blocking drugs by using slow and fast frequencies of indirect stimulation on partial twitch depression in vitro.
METHODS
A rat phrenic nerve hemidiaphragm was dissected and was mounted in an organ bath containing an oxygenated Krebs solution. The phrenic nerve was stimulated supramaximally and the twitch response (0.1 Hz) was stabilized for at least 30 minutes. T200/T1 ratio (twitch height of the 200th stimuli divided by that of the first stimuli) at frequencies of 0.2, 0.5, 1.0, and 2.0 Hz using a drug concentration which provided approximately 20% twitch depression at 0.1 Hz was calculated. To compare T200/T1 ratios with TOF ratios, a 2.0 Hz TOF response was measured immediately after the 200th stimuli at either frequency of stimulation.
RESULTS
T200/T1 ratios produced by succinylcholine (SCC) and decamethonium (C10) were located between alpha-bungarotoxin (ABX) and hexamethonium (C6), however, significant differences among the four drugs were found at 2.0 Hz. The propensity for a decrease in T200/T1 ratios at 2.0 Hz might differ from this study: C6 > C10 > SCC > ABX. T200/T1 ratios at 2.0 Hz were not different from TOF ratios.
CONCLUSIONS
It is concluded that small doses of C10 have a greater presynaptic activity than that of SCC, when the observed effects in this study were compared with the result of ABX acting predominantly at postsynaptic receptors and C6 acting predominantly at presynaptic receptors.

Key Words: Neuromuscular relaxants: alpha-bungarotoxin; decamethonium; hexamethonium; succinylcholine; Neuromuscular transmission: twitch response