The contraction of the muscle cells of arteries is triggered by calcium entering the cell, which it does through special channels in the cell membrane known as calcium channels. As their name implies, calcium channel blockers (also known as calcium antagonists) plug the entrance to these channels and weaken the contraction of the muscle cell. This relaxation dilates the artery and lowers the blood pressure. The contraction of heart muscle is also calcium-dependent, but the configuration of the channels is slightly different, so that some of the calcium channel blockers have effects on the heart, while others do not. Their ability to dilate coronary arteries accounts for their effectiveness in angina as well as in hypertension.
Calcium channel blockers are widely used for the treatment of high blood pressure and angina, but a few years ago, came under fire because of reports that they might cause heart attacks. This, however, applied only to the short-acting form of nifedipine (Procardia or Adalat), which was actually never approved for the treatment of high blood pressure, and produces a 'yo-yo' effect on blood pressure. It is generally thought that the long-acting forms (all the ones currently recommended for treating hypertension) are quite safe, because they lower the pressure much more gradually and smoothly. In elderly patients with hypertension, one of them (nitrendipine) has been shown to prevent strokes and heart attacks.
