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The channel has a large diameter of 0.8x1.1nm, and is non-selective for small ions. However, it has an upper exclusion size limit corresponding to molecular weights of about 600 Dalton of permeants. Because most metabolites have molecular weights lower than 600 Da and have been shown to pass through porin channels, porins are called general diffusion pores.
There are two basic types of calcium channel blockers: dihydropyridine and non-dihydropyridine. The most important difference between the two types is that non-dihydropyridine calcium channel blockers can slow down the heart rate, while dihydropyridine calcium channel blockers do not. Nifedipine is a dihydropyridine calcium channel blocker, which means that it does not usually decrease the heart rate.