+ ▁and ▁K + ▁across ▁the ▁re ceptor ▁causes ▁dep olar ization , ▁the ▁end - plate ▁potential , ▁that ▁opens ▁voltage - g ated ▁sod ium ▁channels , ▁which ▁allows ▁for ▁firing ▁of ▁the ▁action ▁potential ▁and ▁potentially ▁mus cular ▁contra ction . ▁ ▁m A Ch R ▁ ▁In ▁contrast , ▁the ▁m A Ch R s ▁are ▁not ▁ion ▁channels , ▁but ▁belong ▁instead ▁to ▁the ▁super family ▁of ▁G - prote in - cou ple d ▁re cept ors ▁that ▁activ ate ▁other ▁ion ic ▁channels ▁via ▁a ▁second ▁mess enger ▁cas cade . ▁The ▁mus car ine ▁ch ol iner g ic ▁ ▁re ceptor ▁activ ates ▁a ▁G - prote in ▁when ▁bound ▁to ▁ext rac ell ular ▁A Ch . ▁The ▁alpha ▁sub unit ▁of ▁the ▁G - prote in ▁activ ates ▁gu any late ▁cycl ase ▁( in hib iting ▁the ▁effects ▁of ▁int rac ell ular ▁c AMP ) ▁while ▁the ▁beta - gamma ▁sub unit ▁activ ates ▁the ▁K - ch annels ▁and ▁therefore ▁hyper pol ar ize ▁the ▁cell . ▁This ▁causes ▁a ▁decrease ▁in ▁card iac ▁activity . ▁ ▁Ph arm ac ology ▁ ▁Ac et yl ch oline ▁re ceptor ▁mod ul ators ▁can ▁be ▁class ified ▁by ▁which ▁re ceptor ▁sub types ▁they ▁act ▁on : ▁ ▁Ro le ▁in ▁health ▁and ▁disease ▁Nic ot in ic ▁ac et yl ch oline ▁re cept ors ▁can ▁be ▁blocked ▁by ▁cur are , ▁hex am eth on ium ▁and ▁to