L-type (Ca_V1) voltage-gated Ca²⁺ channels are plasma membrane protein complexes which allow the passage of Ca²⁺ ions into cells following depolarization of the membrane potential. L-type channels are widely expressed in cardiac and smooth muscle where they control contraction. Consequently, these channels were recognized as a therapeutic target for cardiovascular diseases^1,2.

Dihydropyridines (DHP) are molecules that act as allosteric modulators of L-type channels. Many are used in the clinic to treat hypertension^2,3. Amlodipine besylate is a DHP that acts as an L-type, voltage-gated Ca²⁺ channel blocker and is used in the clinic to treat hypertension^3,4. Amlodipine inhibits Ca²⁺-induced contractions in depolarised rat aorta (IC₅₀ 1.9 nM) but displays a very slow action onset. Contractions induced by depolarising steps with 45 mM K⁺ are far less potently blocked by amlodipine (IC₅₀ 19.4 nM) and guinea pig papillary muscle single-cell slow action potentials are blocked at a concentration of 5 mM⁴. Amlodipine besylate inhibits L- and T-type Ca_V channels with similar potency⁵.