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The three chemical classes of inhibitors of Ca2+ influx each bind to their own distinct receptor. The three receptor sites are all located within the α1-subunit of the L-type Ca2+ channel. The three receptors overlap one another so that allosteric interaction occurs between drugs from the different classes. Verapamil gains access to its receptor from the intracellular side of the cell membrane. In contrast diltiazem and the dihydropyridines access their receptors from the extracellular side of the cell membrane (click to see this).
