How and what do all of these medication Blockers block?

Many patients may hear that the medication that their doctor is prescribing them is a sodium channel blocker, Beta-blocker, potassium channel blocker, or a calcium channel blocker without being told what the difference is or why or how they work so well. Patients may be wondering...is Beta the letter of my fraternity that has come back to haunt me after all these years? As you will see, sodium, "Beta", potassium and calcium are not some evil little molecules out to get your heart. They are very vital aspects of your bodily functions but can sometimes become overstimulated, cause arrhythmias and those funky channel blockers become just what the doctor orders. For now, I will just review Sodium Channel Blockers and Beta Blockers. Please stay tuned for a future blog in which I will review Potassiam and Calcium Channel-Blockers.

Class I: Sodium Channel Blockers

Action Potentials & The Role Sodium Channels Play in Action Potentials
An action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls. These occur in excitatory cells, such as neurons. In muscle cells, an action potential is the first step in the chain of events leading to contraction. Action potentials are often referred to as "spikes" or a neuron "firing." They are generated by special types of voltage-gated ion channels spanning the cell membrane. When the cell is resting, the channels are closed and are inactive. But if the membrane potential increases to a defined threshold value, the channels quickly open and allow ion movement across the membrane. This opening of the ion channels allows sodium to move into the cell, which further increases the membrane potential. More sodium channels open as a result, producing a greater electrical current. When all of the sodium ion channels are open, the cell is now more positive on the inside than on the outside; therefore, positive charge will want to leave the cell to attempt to reach the original threshold value at the resting potential. Therefore potassium channels are opened and potassium is released from the cell and the cell returns to its resting potential.

What a Sodium Channel Blocker Blocks and What They are Used for Treating
Sodium channel blockers reduce the exitogenicity of the cell membranes. Usually the phase depolarization (the moment that sodium usually flows in quickly and causes the cell to become more positive) is depressed. This prolongs the action potential by slowing conduction and decreases conductivity.

Sodium channel blockers are used for treating atrial fibrillation(Class Ia), atrial flutter (Ia), supraventricular (Ia) and ventricular tachyarrhythmias (Class Ia & IIb & Ic).

Examples of Sodium Channel Blockers and Their Side Effects
Ia: Quinidine, Procainamide, Disopryamide
Ib: Lidocaine, Tocainide, Mexiletine, Phenytoin (Brand=Dilantin)
Ic: Flecainide, Propafenone, Moricizine

Side effects include: Tachycardia, dry mouth, urinary retention, blurred vision, constipation, diarrhea, nausea, headache, and dizziness. Of course, not all Sodium Channel blockers have all of these side effects. Talk with your doctor and your pharmacist to find out what the right drug is for you. And don't forget to rate the drug on www.RateaDrug.com to let others know what experiences you had with a specific medication!

Class II: Beta-Blockers

How Beta Receptors Normally Operate
Most people have experienced adrenaline rushes and know that it's a chemical that does some quite amazing things to our bodies. Adrenaline is also known as epinephrine and it acts by binding to receptors on the outside (membrane) of our cells. The receptors specialized for epinephrine are called Beta-adrenergic receptors and are made of 7 alpha helices spanning the cell membrane. Once epinephrine is bound to the receptor, the receptor is activated and a signal transduction cascade begins that ultimately stimulates the breakdown of glycogen for energy. First, the cytoplasmic loops (inside the cell) that connect the alpha helices together change their conformation. A β-adrenergic receptor mediates its effects via a class of peripheral membrane proteins known as the heterotrimeric G-proteins. It has 3 subunits, alpha (α), beta (β), and gamma (γ). In the inactive state, GDP is bound to the alpha subunit and when activated, this GDP molecule leaves and GTP takes its place. The beta-gamma dimer dissociates from the alpha subunit. This activation of the G protein activates adenylyl cyclase, which activates cyclic AMP (cAMP). cAMP bind to Protein Kinase A (PKA), activating PKA. PKA is a key regulator of the breakdown of glycogen and the body receives a sudden burst of energy!

What a Beta-Blocker Blocks and What They are Used for Treating
Beta-blockers are drugs that block norepinephrine and epinephrine (adrenaline) from binding to beta receptors on nerves. By blocking these neurotransmitters' effects, beta blockers reduce heart rate, reduce blood pressure by dilating blood vessels and may constrict air passages by stimulating the muscles that surround the air passages to contract. There are three types of beta receptor that control a variety of functions based on their location in the body. Beta-1 receptors are located in the heart, eye and kidneys; Beta-2 receptors are located in the lungs, GI tract, liver, uterus, blood vessels and skeletal muscle; Beta-3 receptors are located in fat cells. Beta blockers primarily block the Beta-1 and Beta-2 receptors.

Beta blockers are used for treating arrhythmia (irregular heart rhythms), high blood pressure, heart failure, chest pain (angina), tremors and sometimes prevention of migraines. They are also used after heart attacks to prevent further heart attacks.

Examples of Beta-blockers and Their Side Effects
As you will notice, the Beta-blockers listed below all end in "-lol."
Acebutolol
Atenolol
Bisoprolol
Carvedilol (Coreg)
Metoprolol (Toprol or Lopressor)
Nadolol
Pindolol
Propranolol
Sotalol
Timolol

The side effects of beta blockers may cause diarrhea, stomach cramps, nausea, vomiting, rash, blurred vision, muscle cramps, fatigue, headache, dizziness, confusion, depression, nightmares, hallucinations, shortness of breath in asthmatics and may cause low blood pressure. Of course, not all Beta-blockers have all of these side effects. Sudden withdrawal of Beta blockers may worsen chest pain and cause heart attacks. Talk with your doctor and your pharmacist to find out what the right drug is for you. And don't forget to rate the drug on www.RateaDrug.com to let others know what experiences you had with a specific medication!