Sodium-Potassium Pump & Plasma Membrane
- Na+-K+ ATPase is located in the plasma membrane with ATP site on cytosolic side. For each ATP consumed, 3Na+ go out of the cell (pump phosphorylated) and 2K+ come into the cell (pump dephosphorylated).
- Plasma membrane is an asymmetric lipid bilayer containing cholesterol, phospholipids, sphingolipids, glycolipids, and proteins.
- Pumpkin = pump K+ in.
- Ouabain (a cardiac glycoside) inhibits by binding to K+ site.
- Cardiac glycosides (digoxin and digitoxin) directly inhibit the Na+-K+ ATPase, which leads to indirect inhibition of Na+/Ca2+ exchange →↑ [Ca2+]i →↑ cardiac contractility.
- Digoxin slows AV nodal conduction speed by sensitizing arterial baroreceptors (eg, carotid, aortic) and cardiac receptors, augmenting afferent input from the cardiovascular system to the brain, also by augmenting vagal parasympathetic tone decreases action potential duration, can cause QT interval shortening.