▁a ▁form ▁of ▁a version ▁ther apy ▁in ▁the ▁ 1 9 6 0 s ▁and ▁ 1 9 7 0 s ▁in ▁some ▁prison ▁and ▁institution al ▁settings . ▁This ▁use ▁was ▁dis cont in ued ▁after ▁negative ▁public ity ▁concerning ▁the ▁ter r ifying ▁effects ▁on ▁subjects ▁of ▁this ▁treatment ▁and ▁eth ical ▁questions ▁about ▁the ▁pun itive ▁use ▁of ▁pain ful ▁a version . ▁ ▁Mechan ism ▁of ▁action ▁There ▁are ▁two ▁phases ▁to ▁the ▁blocking ▁effect ▁of ▁su x am eth on ium . ▁ ▁Ph ase ▁ 1 ▁block ▁ ▁Ph ase ▁ 1 ▁blocking ▁has ▁the ▁principal ▁par al yt ic ▁effect . ▁Binding ▁of ▁su x am eth on ium ▁to ▁the ▁nic ot in ic ▁ac et yl ch oline ▁re ceptor ▁results ▁in ▁opening ▁of ▁the ▁re ceptor ' s ▁mon oval ent ▁c ation ▁channel ; ▁a ▁dis organ ized ▁dep olar ization ▁of ▁the ▁motor ▁end - plate ▁occurs ▁and ▁calci um ▁is ▁released ▁from ▁the ▁s arc op las mic ▁ret icul um . ▁ ▁In ▁normal ▁ske let al ▁mus cle , ▁ac et yl ch oline ▁dis soci ates ▁from ▁the ▁re ceptor ▁following ▁dep olar ization ▁and ▁is ▁rapidly ▁hydro ly zed ▁by ▁the ▁en zym e ▁ac et yl ch olin ester ase . ▁The ▁mus cle ▁cell ▁is ▁then ▁ready ▁for ▁the ▁next ▁signal . ▁ ▁S ux am eth on ium ▁has ▁a ▁longer ▁duration ▁of ▁effect ▁than ▁ac et yl ch oline , ▁and