Question: The drug Nifedipine is mentioned in this chapter as a membrane calcium ion channel blocker, and it is used to relax the walls of blood vessels (effectively lowering high blood pressure). Explain step-by-step how blocking membrane calcium channels could have this effect, especially considering that smooth muscle has no troponin. Second, the drug is also used to slow down labor during childbirth, presumably by its action on the uterus. Would that work similarly to Nifedipine's effect on blood vessel walls?