1.+How+Digitalis+Works

Digitalis, also known as digitoxin or digoxin, is a drug derived from the Purple Foxglove Flower (Digitalis Pupure) which can be used to make the heart beat more efficiently.

Strong contractions are essential to good cardiac health. As a heart ages, it may weaken, causing the pumping mechanism to become less effective. Blood may not be pushed out of the heart at a fast enough rate to make room for new blood, and because of this, the volume of blood in the heart increases, causing the congested feeling characteristic of Congestive Heart Failure. Several cardiac glycosides, a class of cardiac steroids containing a steroid nucleus, a lactone ring, and polysaccharide chains, can be extracted from leaves of the digitalis plant. These Cardiac Steroids can be used to increase the force of a heart's contractions. Digitoxin uses these steroids to increase the concentration of calcium ions inside the heart muscles. Calcium ions (Ca ++) are strong triggers for muscle contractions.

For a heart muscle cell at rest, relative concentrations are high for potassium cations inside of the cell membrane, and for sodium and calcium cations outside. Electrical stimulation of the cell (membrane depolarization) causes a quick increase in the concentration of sodium inside the cell, which then more slowly also draws calcium cations inside, and finally causes potassium to move to the outside. At this point, the higher concentration of calcium cations inside the cell triggers a contraction by allowing a temporary binding between two proteins, actin and myosin. Tropomyosin molecules usually inhibit myosin from binding to actin by sitting in the attachment sites on the Actin. Calcium ions are able to move the tropomyosin out of the way, and thus, start a heart muscle contraction. The cell then prepares for the next heartbeat by returning to the sodium/potassium/calcium balance of its resting state. This movement of ions is achieved by enzymes in a membrane-bound Na+-K+-ATPase pump. This process is shown in the graphic below:



Digoxin from the digitalis plant strengthens the force of heart contractions by binding to this Na+-K+-ATPase pump and inhibiting its activity, causing a higher concentration of sodium to remain in the cell. This causes an increase in the intracellular calcium level, which has the positive effect of making more forceful contractions of the heart muscle.