• The relative importance of electromechanical or pharmacomechanical coupling for any given smooth muscle preparation can be estimated by determining the effects of inhibitors of VOCC’s on the contraction to agonists. • For example, in guinea pig ileum, dihydropyridines such as nifedipine will virtually abolish all contractions, suggesting that electromechanical coupling predominates • However, both mechanisms probably occur to some extent in all smooth muscle.  In addition, the opening of ROCC and SOCC also produce membrane depolarization, thus activating electromechanical coupling.