Final answer:
Among the drugs listed, Lignocaine does not prolong the refractory period in normal cells since it is a sodium channel blocker, contrasting with the other drugs which are potassium channel blockers.
Step-by-step explanation:
The question pertains to drugs that affect the refractory period in normal cardiac cells. Specifically, it asks which of the given drugs does not prolong the refractory period. The refractory period is a phase during the cardiac action potential when the heart muscle cells are unable to fire again, which is essential for proper heart function. Among the listed options, Lignocaine (also known as Lidocaine), Amiodarone, Procainamide, and Quinidine, all of the drugs except Lignocaine act by blocking potassium channels, prolonging the refractory period. Lignocaine, on the other hand, is a sodium channel blocker, and therefore does not have the same effect on the refractory period in normal cells.
Potassium channel blockers like amiodarone and procainamide are used to treat cardiac dysrhythmias and work by impeding the movement of K+ through voltage-gated K+ channels. This action primarily affects the repolarization phase of the action potential. By blocking this part of the action potential, these drugs prolong the refractory period, which can help prevent abnormal heart rhythms.
Lidocaine's primary function as a sodium channel blocker makes it an effective local anesthetic because by blocking sodium channels, it inhibits neuronal transmission at the site of administration, preventing the initiation and propagation of nerve impulses responsible for pain sensation.