Chapter 11 - Section 11.7 - Cardiac and Smooth Muscle - Apply What You Know - Page 427: 1

Calcium channel blockers are a class of drugs that primarily affect the contraction of smooth muscle, as well as cardiac muscle, by targeting calcium channels in cell membranes. These drugs have important clinical applications, particularly in managing conditions related to blood pressure, angina, and certain arrhythmias. Here's how calcium channel blockers affect smooth muscle contraction: 1. **Normal Mechanism of Smooth Muscle Contraction**: - In smooth muscle cells, including those found in blood vessels and the gastrointestinal tract, calcium ions (Ca2+) play a crucial role in initiating and regulating muscle contraction. - When smooth muscle cells are stimulated to contract, calcium ions enter the cells through specialized voltage-gated calcium channels located in the cell membrane. 2. **Action of Calcium Channel Blockers**: - Calcium channel blockers, as the name suggests, inhibit the activity of these voltage-gated calcium channels. - By binding to and blocking these calcium channels, these drugs reduce the influx of calcium ions into smooth muscle cells. 3. **Effects on Smooth Muscle Contraction**: - Reduced calcium influx has several significant effects on smooth muscle contraction: - **Decreased Intracellular Calcium Levels**: Calcium channel blockers lead to lower intracellular calcium levels in smooth muscle cells. - **Inhibition of Contraction**: With reduced intracellular calcium, the ability of the contractile proteins actin and myosin to interact and generate force is diminished. - **Relaxation of Smooth Muscle**: Smooth muscle relaxation occurs as a result of decreased contractile activity. 4. **Clinical Applications**: - Calcium channel blockers are used therapeutically to achieve various effects on smooth muscle, depending on the specific drug and its target tissue. - **Vasodilation**: By relaxing the smooth muscle in blood vessel walls, calcium channel blockers reduce peripheral resistance and dilate blood vessels. This leads to a reduction in blood pressure, making them useful in treating hypertension (high blood pressure). - **Coronary Vasodilation**: Some calcium channel blockers, like those of the dihydropyridine class, primarily affect the smooth muscle in coronary arteries, leading to increased blood flow to the heart and reduced angina (chest pain). - **Gastrointestinal Effects**: In the gastrointestinal tract, calcium channel blockers can reduce smooth muscle contractions, potentially alleviating conditions like esophageal spasms or irritable bowel syndrome (IBS). - **Uterine Relaxation**: Calcium channel blockers can also affect smooth muscle in the uterus, potentially reducing uterine contractions during preterm labor. In summary, calcium channel blockers exert their effects on smooth muscle contraction by inhibiting the influx of calcium ions into muscle cells. This leads to relaxation of the smooth muscle, making these drugs valuable for treating conditions where reducing smooth muscle contractility is medically beneficial.

Calcium channel blockers are a class of drugs that primarily affect the contraction of smooth muscle, as well as cardiac muscle, by targeting calcium channels in cell membranes. These drugs have important clinical applications, particularly in managing conditions related to blood pressure, angina, and certain arrhythmias. Here's how calcium channel blockers affect smooth muscle contraction: 1. **Normal Mechanism of Smooth Muscle Contraction**: - In smooth muscle cells, including those found in blood vessels and the gastrointestinal tract, calcium ions (Ca2+) play a crucial role in initiating and regulating muscle contraction. - When smooth muscle cells are stimulated to contract, calcium ions enter the cells through specialized voltage-gated calcium channels located in the cell membrane. 2. **Action of Calcium Channel Blockers**: - Calcium channel blockers, as the name suggests, inhibit the activity of these voltage-gated calcium channels. - By binding to and blocking these calcium channels, these drugs reduce the influx of calcium ions into smooth muscle cells. 3. **Effects on Smooth Muscle Contraction**: - Reduced calcium influx has several significant effects on smooth muscle contraction: - **Decreased Intracellular Calcium Levels**: Calcium channel blockers lead to lower intracellular calcium levels in smooth muscle cells. - **Inhibition of Contraction**: With reduced intracellular calcium, the ability of the contractile proteins actin and myosin to interact and generate force is diminished. - **Relaxation of Smooth Muscle**: Smooth muscle relaxation occurs as a result of decreased contractile activity. 4. **Clinical Applications**: - Calcium channel blockers are used therapeutically to achieve various effects on smooth muscle, depending on the specific drug and its target tissue. - **Vasodilation**: By relaxing the smooth muscle in blood vessel walls, calcium channel blockers reduce peripheral resistance and dilate blood vessels. This leads to a reduction in blood pressure, making them useful in treating hypertension (high blood pressure). - **Coronary Vasodilation**: Some calcium channel blockers, like those of the dihydropyridine class, primarily affect the smooth muscle in coronary arteries, leading to increased blood flow to the heart and reduced angina (chest pain). - **Gastrointestinal Effects**: In the gastrointestinal tract, calcium channel blockers can reduce smooth muscle contractions, potentially alleviating conditions like esophageal spasms or irritable bowel syndrome (IBS). - **Uterine Relaxation**: Calcium channel blockers can also affect smooth muscle in the uterus, potentially reducing uterine contractions during preterm labor. In summary, calcium channel blockers exert their effects on smooth muscle contraction by inhibiting the influx of calcium ions into muscle cells. This leads to relaxation of the smooth muscle, making these drugs valuable for treating conditions where reducing smooth muscle contractility is medically beneficial.