Ans: b) (Smooth muscle) Ref: Katzung 11th edition and Cardiovascular Pharmacology ConceptsCCBs bind to L-type calcium channels located on the vascular smooth muscle, cardiac myocytes, and cardiac nodal tissue (SA and AV nodes).These channels are responsible for regulating the influx of calcium into muscle cells, which in turn stimulates smooth muscle contraction and cardiac myocyte contraction.In cardiac nodal tissue, L-type calcium channels play an important role in pacemaker currents and in phase 0 of the action potentials.Therefore, by blocking calcium entry into the cell, CCBs cause:vascular smooth muscle relaxation (vasodilation),decreased myocardial force generation (negative inotropy),decreased heart rate (negative chronotropy), and decreased conduction velocity within the heart ( negative dromotropy), particularly at the atrioventricular node.In addition to their antianginal and antiarrhythmic effects, thus calcium channel blockers also reduce peripheral resistance and blood pressure.NB: CCB's do not work on venous smooth muscleThree types of Ca2+ channels have been described:a) Voltage sensitive channelb) Receptor operated channelc) Leak channelThe voltage sensitive channel are further divided into 3 types:L-type (long lasting current),T-type (transient current) andN type (neuronal)There was question in 2005 kerala regarding CCBs which act both on L and T subtypes ofCa2+ channels.Even after a lot of reference it was found that only the voltage sensitive L-type channels are blocked by CCBs.