Cardiac Drugs 5 of 5 - calcium channel blocker

Cardiac Drugs Series- #5

In this series we briefly overview those drugs that our cardiac patients take for blood pressure control.
Check out our first four episodes on
ACE inhibitors (prils)
Ang2Receptor blockers (Sartans)
Beta blockers (lols)
Loop diuretics

Continuing in the same Antihypertensive (blood pressure lowering) theme, this episode looks at Calcium Channel Blockers. (Ca2+ blockers)

Before we start, we should review the normal role of calcium in our heart and blood vessels.   Muscle in the heart and smooth muscle in the walls of arteries (where blood pressure is regulated), requires calcium to flush into muscle cells to contract.

 Reflecting on basic electrolyte and cell physiology, you may recall that calcium ion concentrations outside cells is about 10 thousand times higher than Ca2+ levels inside cells.
At a microscopic level, the membrane of muscle cells (all cells) have tiny gates that open and close to allow specific substances into (influx) and out of (efflux) the cell.  As expected, cells have calcium specific gates (channels), which open when electrically stimulated (action potential).

Once these channels (gates) open, calcium influxes into the muscle cell and is used by the muscle cell to initiate a conformational change (muscle cell contraction).

Recognising that a contracted muscular wall of an artery results in an increase of pressure (blood is squeezed), it stands to reason that if I can give you a drug that blocks or prevents these calcium gates (channels) opening.

The result is impaired ability for the artery to contract or constrict .
The resulting relaxation of the artery causes there to be more space for blood= less arterial pressure. For all the same physiological reasons, calcium channel blocker act on cardiac muscle to reduce the force of the heart contraction.

A secondary effect that causes the reduction of heart rate is that calcium blockade reduces the speed of electrical impulses through the heart.

Examples of these drugs include verapamil and nifedipine.

Some (nifedipine) are fast acting, and effective in inhibiting smooth muscle contraction in hypertensive crisis, or premature labour.

Others are longer acting and used as another weapon against hypertension, and tachyarrythmias like SVT.

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