TY - JOUR T1 - DEPOLARIZING NEUROMUSCULAR BLOCK JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 339 LP - 349 VL - 178 IS - 2 AU - ANIBAL GALINDO Y1 - 1971/08/01 UR - http://jpet.aspetjournals.org/content/178/2/339.abstract N2 - Simultaneous recording of tension output and intracellular potentials was made in rat diaphragms contracting isometrically. There were two types of responses to the administration of succinylcholine and decamethonium. An "initial" response characterized by: 1) transient increase in the strength of muscular contractions, 2) 5 to 10 mV depolarization of the end-plate membrane, 3) sudden disappearance of end-plate potentials with preservation of miniature end-plate potentials and 4) well maintained strength of muscular contractions during tetanic stimulation of the phrenic nerve (100 Hz) in partially paralyzed muscles. A different response, the "late" response, was observed if succinylcholine or decamethonium was administered: a) a second time after a previous administration of no more than 20 minutes (tachyphylaxis), b) a second time after more than 60 minutes of continuous succinylcholine or decamethonium soaking or 3) continuously (60-180 minutes) at low concentrations. During the late response end-plate depolarization was nil, miniature end-plate potentials and end-plate potentials progressively decreased in amplitude whereas the strength of muscular contractions was no longer well maintained during tetanic stimulation. The late response was identified as "phase II" block. The results presented in this paper are consistent with a relatively more important action of depolarizing muscle relaxants on motor nerve terminals. © 1971 by The Williams & Wilkins Co. ER -