Cardiac Muscle Physiology Flashcards
Pacemaker activity of the heart is generally regarded as:
Automaticity
How does the heart regulate force of contraction?
Titrating Calcium levels via inotropism
What is a syncytium?
Arrangement of muscle fibers in which the fibers fuse to form an interconnected mass of fibers. Gap junctions within the heart.
Fast channels within the heart:
Voltage activated sodium channels
Slow channels within the heart
Voltage activated calcium channels
In cardiac muscle the sarcoplastic reticulum forms a Diad or Triad?
Diad: for communication between two cardiomyocytes
Which ion is essential to cardiac muscle contraction?
Calcium
Inotropism
The ability of the myocardial cells to change the force/strength at the level of the cell and this modification can occur independently of any change in force caused by alterations in preload or afterload on the heart
Anrep Effect
Abrupt increase in afterload produces modest increase in inotropy
Bowditch effect
Increase in heart rate produces a small (+) inotropic effect
Factors that increase inotropy in the cardiomyocyte tissue
- Parasympathetic inhibition
- Sympathetic Activation
- Circulating catecholamines
- Heart rate (Bowditch Effect)
- Afterload (Anrep Effect)
(+) Inotropic Drugs
Digoxin
Beta Agonists: Gs-Protein linked receptors:
1. Dopamine
2. Dobutamine
3. Epinephrine
Phosphodiesterase inhibitors: increase cAMP: Milrinone
Which drug inhibits Na+/K+ ATPase, which decreases the gradient of Na+ and therefore indirectly inhibits Na+/Ca2+ exchanger?
Digoxin
What is digoxin used for clinically?
Cardiac glycoside: Systolic Heart Failure
Calcium channel blockers inhibit
Voltage dependent L-type calcium channels, which decrease muscle contractility
Dihydropyridine
Calcium channel blocker that acts on vascular smooth muscle
Calcium Channel Blockers
- Amplodipine
- Clevidipine
- Nicardipine
- Nifedipine
- Nimodipine
Clinical use for calcium channel blockers:
Hypertension, prevention of cerebral vasospasm
Drugs that are non-dihydropyrine Calcium channel blockers and clinical use
- Dilitiazem
- Verapamil
Clinical Use: Atrial Fibrillation
Verapamil use
Atrial fibrillation treatment
Drugs used to treat bronchial asthma
Albuterol, levalbuterol, salmeterol, salbutamol (inhalation)
*Beta-2 agonists (2 lungs mnemonic)
Drugs used to induced uterine smooth muscle relaxation in pregnant women
Terbutaline: tocolysis
-Premature labor
What is milrinone used for?
Short-term use in acute decompensated heart failure
Milrinone is what type of drug?
Selective PDE-3 inhibitor (increases inotropy, chronotropy, general vasodilation in vascular smooth muscle)
MOA of milrinone:
Increase cAMP in cardiomyocytes which increases calcium influx.
-In vascular smooth muscle, increases cAMP, inhibits MLCK activity (myosin light chain kinase)
What are nitrates used for?
Increase in vascular smooth muscle, dilates veins and decrease the preload
Nitroglycerin, isosorbine denitrate, isosorbide mononitrate are examples of what kind of drug and used for which clinical condition?
Nitrates
-Clinical use: angina acute coronary syndrome
Hydralazine
increases cGMP (vascular smooth muscle relaxation)
-Dilates arterioles
-Clinical use: severe hypertension (acute treatment)
Nitroprusside
Increases cGMP: vascular smooth muscle relaxation
Pharmacomechanical coupling of Calcium channel receptor called
Ligand-gated Calcium channels
Electromechanical coupling of calcium channel receptor called
Voltage gated calcium channels
Myogenic regulation in the arterioles calcium channel receptor called
Leak calcium channels
Mechanical stretch promotes inward of calcium
Stretch-activated calcium channels
Which of the following is the most important difference between the myosin II filaments of the smooth and striated muscles:
Actomyosin ATPase activity is much slower in smooth muscle
