Potassium

Potassium ion is the primary intracellular cation found in virtually all body tissues. The total amount of body potassium in adults is estimated at 45 millimole (mmol)/kg body weight (about 140 g for an adult weighing 175 pounds; 1 mmol = 1 milliequivalent or 39.1 mg of potassium). Potassium mainly stays in cells, and a small amount can be found in the extracellular fluid. The amount of potassium that stays in the cell (intracellular) is 30 times that of extracellular concentration, creating a transmembrane gradient, regulated by the sodium-potassium (Na+/K+) ATPase transporter. This is an important gradient for nerve conduction, muscle contractions, and renal function. Vomiting, diarrhea, renal disease, medications, and other conditions that alter potassium excretion or shift it inside or outside of cells. In healthy patients individuals with normal renal function, markedly high or low potassium levels are rare.

Effect on blood pressure

Potassium decreases reduces intravascular volume, by reducing sodium reabsorption through an increase in urinary sodium excretion. This short-term effect, however, does not explain the long-term effects of potassium on blood pressure. Increased plasma potassium levels that occur through intake are associated with vasodilation occurring via stimulation of the sodium-potassium adenosine triphosphatase pump (Na+/-K+ATPase) and opening of potassium channels of the sodium-potassium adenosine triphosphatase pump. Other possible mechanisms of action for potassium may include alterations in barroreflex sensitivity and hormone sensitivity in vascular smooth muscle and cells of the sympathetic nervous system.

Effect on electrolyte balance and body systems

The potassium gradient across the membrane of a cell regulates cell membrane potential, maintained predominantly by the sodium-potassium (Na+/-K+ ATPase pump). Transmembrane electro-chemical gradients encourage diffusion of Na+ extracellularly and K+ intracellularly. Potassium supplementation prevents hypokalemia to maintain this balance and is often used in an oral solution or injection form in the clinical setting, preventing harmful effects such as arrhythmias, abnormal muscle function, and neurological disturbances. When activated, the Na+/-K+ ATPase pump exchanges two extracellular K+ ions for three intracellular sodium (Na+) ions, impacting membrane potential via either excitation or inhibition. This is especially important in the homeostasis of the nervous system, kidney, and cardiac muscle tissue. The body and cell distributions of potassium in normal conditions are known as internal and external balance, respectively. Reduced serum potassium (or imbalance) increases the risk of ventricular arrhythmia, heart failure and left ventricular hypertrophy (LVH).