Calcium Channel Blockers Review Questions and Correct Answers

calcium channel blockers Effect the heart, and blood vessels. CCBs are widely used to treat hypertension, angina pectoris and cardias dysrhythmias. calcium and the heart Calcium regulates contraction in vascular smooth muscle and cardiac muscle. In cardiac/vascular smooth muscle (VSM), the influx of Ca produces the plateaued depolarization in the heart. Causing the cardiac muscle to contract forcefully for longer. Without Ca, the force will diminish. Unlike skeletal muscle, cardiac muscle stays depolarized longer (causing contraction). This is due to *slow-calcium channels* that let Ca in SLOWLY, continuing the depolarization. Also, in cardiac muscle the absolute refractory period will continue until relaxation is underway. In skeletal muscle, you don't have to wait for muscles to relax all the way before another action potential starts. This is why in skeletal muscle, you can have a summation of impulses leading to tetany (continuous contraction). This cannot happen in cardiac muscle, which is good. Because, a heart in tetany can't pump. How CCBs work CCBs block Ca influx in : vascular smooth muscle- causing vasodilation and/or cardiac muscle- causing cardiac suppression Nifedipine *(Adalat CC, Procardia)* is a CCB of the *Dihydropyridine* family. Therapeutic uses: Angina Pectoris, hypertension. Nifedipine blocks Ca channels in VSM and has very little blockade of Ca in the heart. This causes vasodilation and lowers arteriol blood pressure. With *fast-acting Nifedipine* you can get *reflex tachycardia*. WHY? When blood pressure falls rapidly, baroreceptors go off, and the heart is stimulated by the sympathetic nervous system to pick up the pace. And since this drug has little effect on the Ca channels of the heart, it pumps faster. This doesn't happen when blood levels of Nifedipine rise slowly, because baroreceptors only respond to FAST changes. This medication's actions: 1) lower blood pressure 2) increase heart rate and contractile force (transient effect). Beta blockers & reflex tachycardia. there are beta-1 adrenergic receptors coupled with Ca channels in the heart. These are the things that are activated to cause the reflex tachycardia. Nifedipine is often combined with a beta blocker med to prevent reflex tachycardia. Other side effects of Nifedipine peripheral edema, orthostatic hypotension, suppression of cardiac function (more with other drugs in this family than Nifedipine), acute toxicity Other CCB drug prototypes *Verapamil (Calan)* *Diltiazem (Cardizem)*