消化道平滑肌动作电位产生的主要原因是

A、Na[img=~\/QImg\/2013-06-27-14-49-35\/image001.gif]内流
B、Ca[img=~\/QImg\/2013-06-27-14-49-35\/image006.gif]内流
C、K[img=~\/QImg\/2013-06-27-14-49-35\/image001.gif]内流
D、K[img=~\/QImg\/2013-06-27-14-49-35\/image001.gif]外流
E、Cl[img=~\/QImg\/2013-06-27-14-49-35\/image007.gif]外流